     [file version.texi not included]

Copyright © 2012, 2013, 2014, 2015, 2016 Ludovic Courtès

Copyright © 2013, 2014, 2016 Andreas Enge

Copyright © 2013 Nikita Karetnikov

Copyright © 2014, 2015, 2016 Alex Kost

Copyright © 2015, 2016 Mathieu Lirzin

Copyright © 2014 Pierre-Antoine Rault

Copyright © 2015 Taylan Ulrich Bayırlı/Kammer

Copyright © 2015, 2016 Leo Famulari

Copyright © 2015, 2016 Ricardo Wurmus

Copyright © 2016 Ben Woodcroft

Copyright © 2016 Chris Marusich

Copyright © 2016 Efraim Flashner

Copyright © 2016 John Darrington

Copyright © 2016 ng0

Copyright © 2016 Jan Nieuwenhuizen

Copyright © 2016 Julien Lepiller

Copyright © 2016 Alex ter Weele

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.  A copy of the license is included in the section entitled ``GNU Free Documentation License''.

GNU Guix
********

This document describes GNU Guix version VERSION, a functional package management tool written for the GNU system.

Introduction
************

GNU Guix (``Guix'' is pronounced like ``geeks'', or ``ɡiːks'' using the international phonetic alphabet (IPA).) is a package management tool for the GNU system.  Guix makes it easy for unprivileged users to install, upgrade, or remove packages, to roll back to a previous package set, to build packages from source, and generally assists with the creation and maintenance of software environments.

Guix provides a command-line package management interface (see Invoking guix package), a set of command-line utilities (see Utilities), a visual user interface in Emacs (see Emacs Interface), as well as Scheme programming interfaces (see Programming Interface). Its build daemon is responsible for building packages on behalf of users (see Setting Up the Daemon) and for downloading pre-built binaries from authorized sources (see Substitutes).

Guix includes package definitions for many GNU and non-GNU packages, all of which respect the user's computing freedom (https://www.gnu.org/philosophy/free-sw.html).  It is extensible: users can write their own package definitions (see Defining Packages) and make them available as independent package modules (see Package Modules).  It is also customizable: users can derive specialized package definitions from existing ones, including from the command line (see Package Transformation Options).

You can install GNU Guix on top of an existing GNU/Linux system where it complements the available tools without interference (see Installation), or you can use it as part of the standalone Guix System Distribution or GuixSD (see GNU Distribution). With GNU GuixSD, you declare all aspects of the operating system configuration and Guix takes care of instantiating the configuration in a transactional, reproducible, and stateless fashion (see System Configuration).

Under the hood, Guix implements the functional package management discipline pioneered by Nix (see Acknowledgments). In Guix, the package build and installation process is seen as a function, in the mathematical sense.  That function takes inputs, such as build scripts, a compiler, and libraries, and returns an installed package.  As a pure function, its result depends solely on its inputs---for instance, it cannot refer to software or scripts that were not explicitly passed as inputs.  A build function always produces the same result when passed a given set of inputs.  It cannot alter the environment of the running system in any way; for instance, it cannot create, modify, or delete files outside of its build and installation directories.  This is achieved by running build processes in isolated environments (or containers), where only their explicit inputs are visible.

The result of package build functions is cached in the file system, in a special directory called the store (see The Store).  Each package is installed in a directory of its own in the store---by default under /gnu/store.  The directory name contains a hash of all the inputs used to build that package; thus, changing an input yields a different directory name.

This approach is the foundation for the salient features of Guix: support for transactional package upgrade and rollback, per-user installation, and garbage collection of packages (see Features).

Installation
************

GNU Guix is available for download from its website at http://www.gnu.org/software/guix/.  This section describes the software requirements of Guix, as well as how to install it and get ready to use it.

Note that this section is concerned with the installation of the package manager, which can be done on top of a running GNU/Linux system.  If, instead, you want to install the complete GNU operating system, see System Installation.

When installed on a running GNU/Linux system---thereafter called a foreign distro---GNU Guix complements the available tools without interference.  Its data lives exclusively in two directories, usually /gnu/store and /var/guix; other files on your system, such as /etc, are left untouched.

Binary Installation
===================

This section describes how to install Guix on an arbitrary system from a self-contained tarball providing binaries for Guix and for all its dependencies.  This is often quicker than installing from source, which is described in the next sections.  The only requirement is to have GNU tar and Xz.

Installing goes along these lines:

 1. Download the binary tarball from ftp://alpha.gnu.org/gnu/guix/guix-binary-VERSION.SYSTEM.tar.xz, where SYSTEM is x86_64-linux for an x86_64 machine already running the kernel Linux, and so on.

     Make sure to download the associated .sig file and to verify the authenticity of the tarball against it, along these lines:

          $ wget ftp://alpha.gnu.org/gnu/guix/guix-binary-VERSION.SYSTEM.tar.xz.sig
          $ gpg --verify guix-binary-VERSION.SYSTEM.tar.xz.sig

     If that command fails because you do not have the required public key, then run this command to import it:

          $ gpg --keyserver pgp.mit.edu --recv-keys 3CE464558A84FDC69DB40CFB090B11993D9AEBB5

     and rerun the gpg --verify command.

 2. As root, run:

          # cd /tmp
          # tar --warning=no-timestamp -xf \
               guix-binary-VERSION.SYSTEM.tar.xz
          # mv var/guix /var/ && mv gnu /

     This creates /gnu/store (see The Store) and /var/guix. The latter contains a ready-to-use profile for root (see next step.)

     Do not unpack the tarball on a working Guix system since that would overwrite its own essential files.

     The --warning=no-timestamp option makes sure GNU tar does not emit warnings about ``implausibly old time stamps'' (such warnings were triggered by GNU tar 1.26 and older; recent versions are fine.) They stem from the fact that all the files in the archive have their modification time set to zero (which means January 1st, 1970.)  This is done on purpose to make sure the archive content is independent of its creation time, thus making it reproducible.

 3. Make root's profile available under ~/.guix-profile:

          # ln -sf /var/guix/profiles/per-user/root/guix-profile \
                   ~root/.guix-profile

 4. Create the group and user accounts for build users as explained below (see Build Environment Setup).

 5. Run the daemon, and set it to automatically start on boot.

     If your host distro uses the systemd init system, this can be achieved with these commands:

          # ln -s ~root/.guix-profile/lib/systemd/system/guix-daemon.service \
                  /etc/systemd/system/
          # systemctl start guix-daemon && systemctl enable guix-daemon

     If your host distro uses the Upstart init system:

          # ln -s ~root/.guix-profile/lib/upstart/system/guix-daemon.conf /etc/init/
          # start guix-daemon

     Otherwise, you can still start the daemon manually with:

          # ~root/.guix-profile/bin/guix-daemon --build-users-group=guixbuild

 6. Make the guix command available to other users on the machine, for instance with:

          # mkdir -p /usr/local/bin
          # cd /usr/local/bin
          # ln -s /var/guix/profiles/per-user/root/guix-profile/bin/guix

     It is also a good idea to make the Info version of this manual available there:

          # mkdir -p /usr/local/share/info
          # cd /usr/local/share/info
          # for i in /var/guix/profiles/per-user/root/guix-profile/share/info/* ;
            do ln -s $i ; done

     That way, assuming /usr/local/share/info is in the search path, running info guix will open this manual (see Other Info Directories (GNU Texinfo), for more details on changing the Info search path.)

 7. To use substitutes from hydra.gnu.org or one of its mirrors (see Substitutes), authorize them:

          # guix archive --authorize < ~root/.guix-profile/share/guix/hydra.gnu.org.pub

This completes root-level install of Guix.  Each user will need to perform additional steps to make their Guix environment ready for use, see Application Setup.

You can confirm that Guix is working by installing a sample package into the root profile:

     # guix package -i hello

The guix package must remain available in root's profile, or it would become subject to garbage collection---in which case you would find yourself badly handicapped by the lack of the guix command.  In other words, do not remove guix by running guix package -r guix.

The binary installation tarball can be (re)produced and verified simply by running the following command in the Guix source tree:

     make guix-binary.SYSTEM.tar.xz

Requirements
============

This section lists requirements when building Guix from source.  The build procedure for Guix is the same as for other GNU software, and is not covered here.  Please see the files README and INSTALL in the Guix source tree for additional details.

GNU Guix depends on the following packages:

  * GNU Guile (http://gnu.org/software/guile/), version 2.0.7 or later;

  * GNU libgcrypt (http://gnupg.org/);

  * GNU Make (http://www.gnu.org/software/make/).

The following dependencies are optional:

  * Installing GnuTLS-Guile (http://gnutls.org/) will allow you to access https URLs for substitutes, which is highly recommended (see Substitutes).  It also allows you to access HTTPS URLs with the guix download command (see Invoking guix download), the guix import pypi command, and the guix import cpan command.  See how to install the GnuTLS bindings for Guile (GnuTLS-Guile).

  * Installing Guile-JSON (http://savannah.nongnu.org/projects/guile-json/) will allow you to use the guix import pypi command (see Invoking guix import).  It is of interest primarily for developers and not for casual users.

  * Support for build offloading (see Daemon Offload Setup) depends on Guile-SSH (https://github.com/artyom-poptsov/guile-ssh), version 0.10.2 or later.

  * When zlib (http://zlib.net) is available, guix publish can compress build byproducts (see Invoking guix publish).

Unless --disable-daemon was passed to configure, the following packages are also needed:

  * SQLite 3 (http://sqlite.org);

  * libbz2 (http://www.bzip.org);

  * GCC's g++ (http://gcc.gnu.org), with support for the C++11 standard.

When configuring Guix on a system that already has a Guix installation, be sure to specify the same state directory as the existing installation using the --localstatedir option of the configure script (see localstatedir (GNU Coding Standards)).  The configure script protects against unintended misconfiguration of LOCALSTATEDIR so you do not inadvertently corrupt your store (see The Store).

When a working installation of the Nix package manager (http://nixos.org/nix/) is available, you can instead configure Guix with --disable-daemon.  In that case, Nix replaces the three dependencies above.

Guix is compatible with Nix, so it is possible to share the same store between both.  To do so, you must pass configure not only the same --with-store-dir value, but also the same --localstatedir value.  The latter is essential because it specifies where the database that stores metadata about the store is located, among other things.  The default values for Nix are --with-store-dir=/nix/store and --localstatedir=/nix/var. Note that --disable-daemon is not required if your goal is to share the store with Nix.

Running the Test Suite
======================

After a successful configure and make run, it is a good idea to run the test suite.  It can help catch issues with the setup or environment, or bugs in Guix itself---and really, reporting test failures is a good way to help improve the software.  To run the test suite, type:

     make check

Test cases can run in parallel: you can use the -j option of GNU make to speed things up.  The first run may take a few minutes on a recent machine; subsequent runs will be faster because the store that is created for test purposes will already have various things in cache.

It is also possible to run a subset of the tests by defining the TESTS makefile variable as in this example:

     make check TESTS="tests/store.scm tests/cpio.scm"

By default, tests results are displayed at a file level.  In order to see the details of every individual test cases, it is possible to define the SCM_LOG_DRIVER_FLAGS makefile variable as in this example:

     make check TESTS="tests/base64.scm" SCM_LOG_DRIVER_FLAGS="--brief=no"

Upon failure, please email bug-guix@gnu.org and attach the test-suite.log file.  Please specify the Guix version being used as well as version numbers of the dependencies (see Requirements) in your message.

Guix also comes with a whole-system test suite that tests complete GuixSD operating system instances.  It can only run on systems where Guix is already installed, using:

     make check-system

or, again, by defining TESTS to select a subset of tests to run:

     make check-system TESTS="basic mcron"

These system tests are defined in the (gnu tests ...) modules.  They work by running the operating systems under test with lightweight instrumentation in a virtual machine (VM).  They can be computationally intensive or rather cheap, depending on whether substitutes are available for their dependencies (see Substitutes). Some of them require a lot of storage space to hold VM images.

Again in case of test failures, please send bug-guix@gnu.org all the details.

Setting Up the Daemon
=====================

Operations such as building a package or running the garbage collector are all performed by a specialized process, the build daemon, on behalf of clients.  Only the daemon may access the store and its associated database.  Thus, any operation that manipulates the store goes through the daemon.  For instance, command-line tools such as guix package and guix build communicate with the daemon (via remote procedure calls) to instruct it what to do.

The following sections explain how to prepare the build daemon's environment.  See also Substitutes, for information on how to allow the daemon to download pre-built binaries.

Build Environment Setup
-----------------------

In a standard multi-user setup, Guix and its daemon---the guix-daemon program---are installed by the system administrator; /gnu/store is owned by root and guix-daemon runs as root.  Unprivileged users may use Guix tools to build packages or otherwise access the store, and the daemon will do it on their behalf, ensuring that the store is kept in a consistent state, and allowing built packages to be shared among users.

When guix-daemon runs as root, you may not want package build processes themselves to run as root too, for obvious security reasons.  To avoid that, a special pool of build users should be created for use by build processes started by the daemon. These build users need not have a shell and a home directory: they will just be used when the daemon drops root privileges in build processes.  Having several such users allows the daemon to launch distinct build processes under separate UIDs, which guarantees that they do not interfere with each other---an essential feature since builds are regarded as pure functions (see Introduction).

On a GNU/Linux system, a build user pool may be created like this (using Bash syntax and the shadow commands):

     # groupadd --system guixbuild
     # for i in `seq -w 1 10`;
       do
         useradd -g guixbuild -G guixbuild           \
                 -d /var/empty -s `which nologin`    \
                 -c "Guix build user $i" --system    \
                 guixbuilder$i;
       done

The number of build users determines how many build jobs may run in parallel, as specified by the --max-jobs option (see --max-jobs).  To use guix system vm and related commands, you may need to add the build users to the kvm group so they can access /dev/kvm, using -G guixbuild,kvm instead of -G guixbuild (see Invoking guix system).

The guix-daemon program may then be run as root with the following command (If your machine uses the systemd init system, dropping the PREFIX/lib/systemd/system/guix-daemon.service file in /etc/systemd/system will ensure that guix-daemon is automatically started.  Similarly, if your machine uses the Upstart init system, drop the PREFIX/lib/upstart/system/guix-daemon.conf file in /etc/init.):

     # guix-daemon --build-users-group=guixbuild

This way, the daemon starts build processes in a chroot, under one of the guixbuilder users.  On GNU/Linux, by default, the chroot environment contains nothing but:

  * a minimal /dev directory, created mostly independently from the host /dev (``Mostly'', because while the set of files that appear in the chroot's /dev is fixed, most of these files can only be created if the host has them.);

  * the /proc directory; it only shows the processes of the container since a separate PID name space is used;

  * /etc/passwd with an entry for the current user and an entry for user nobody;

  * /etc/group with an entry for the user's group;

  * /etc/hosts with an entry that maps localhost to 127.0.0.1;

  * a writable /tmp directory.

You can influence the directory where the daemon stores build trees via the TMPDIR environment variable.  However, the build tree within the chroot is always called /tmp/guix-build-NAME.drv-0, where NAME is the derivation name---e.g., coreutils-8.24. This way, the value of TMPDIR does not leak inside build environments, which avoids discrepancies in cases where build processes capture the name of their build tree.

The daemon also honors the http_proxy environment variable for HTTP downloads it performs, be it for fixed-output derivations (see Derivations) or for substitutes (see Substitutes).

If you are installing Guix as an unprivileged user, it is still possible to run guix-daemon provided you pass --disable-chroot. However, build processes will not be isolated from one another, and not from the rest of the system.  Thus, build processes may interfere with each other, and may access programs, libraries, and other files available on the system---making it much harder to view them as pure functions.

Using the Offload Facility
--------------------------

When desired, the build daemon can offload derivation builds to other machines running Guix, using the offload build hook (This feature is available only when Guile-SSH (https://github.com/artyom-poptsov/guile-ssh) is present.).  When that feature is enabled, a list of user-specified build machines is read from /etc/guix/machines.scm; every time a build is requested, for instance via guix build, the daemon attempts to offload it to one of the machines that satisfy the constraints of the derivation, in particular its system type---e.g., x86_64-linux.  Missing prerequisites for the build are copied over SSH to the target machine, which then proceeds with the build; upon success the output(s) of the build are copied back to the initial machine.

The /etc/guix/machines.scm file typically looks like this:

     (list (build-machine
             (name "eightysix.example.org")
             (system "x86_64-linux")
             (host-key "ssh-ed25519 AAAAC3Nza...")
             (user "bob")
             (speed 2.))     ;incredibly fast!

           (build-machine
             (name "meeps.example.org")
             (system "mips64el-linux")
             (host-key "ssh-rsa AAAAB3Nza...")
             (user "alice")
             (private-key
              (string-append (getenv "HOME")
                             "/.ssh/identity-for-guix"))))

In the example above we specify a list of two build machines, one for the x86_64 architecture and one for the mips64el architecture.

In fact, this file is---not surprisingly!---a Scheme file that is evaluated when the offload hook is started.  Its return value must be a list of build-machine objects.  While this example shows a fixed list of build machines, one could imagine, say, using DNS-SD to return a list of potential build machines discovered in the local network (see Guile-Avahi (Using Avahi in Guile Scheme Programs)).  The build-machine data type is detailed below.

 -- Data Type: build-machine
     This data type represents build machines to which the daemon may offload builds.  The important fields are:

     name
          The host name of the remote machine.

     system
          The system type of the remote machine---e.g., "x86_64-linux".

     user
          The user account to use when connecting to the remote machine over SSH. Note that the SSH key pair must not be passphrase-protected, to allow non-interactive logins.

     host-key
          This must be the machine's SSH public host key in OpenSSH format. This is used to authenticate the machine when we connect to it.  It is a long string that looks like this:

               ssh-ed25519 AAAAC3NzaC...mde+UhL hint@example.org

          If the machine is running the OpenSSH daemon, sshd, the host key can be found in a file such as /etc/ssh/ssh_host_ed25519_key.pub.

          If the machine is running the SSH daemon of GNU lsh, lshd, the host key is in /etc/lsh/host-key.pub or a similar file.  It can be converted to the OpenSSH format using lsh-export-key (see Converting keys (LSH Manual)):

               $ lsh-export-key --openssh < /etc/lsh/host-key.pub
               ssh-rsa AAAAB3NzaC1yc2EAAAAEOp8FoQAAAQEAs1eB46LV...

     A number of optional fields may be specified:

     port (default: 22)
          Port number of SSH server on the machine.

     private-key (default: ~/.ssh/id_rsa)
          The SSH private key file to use when connecting to the machine, in OpenSSH format.

     compression (default: "zlib@openssh.com,zlib")
     compression-level (default: 3)
          The SSH-level compression methods and compression level requested.

          Note that offloading relies on SSH compression to reduce bandwidth usage when transferring files to and from build machines.

     daemon-socket (default: "/var/guix/daemon-socket/socket")
          File name of the Unix-domain socket guix-daemon is listening to on that machine.

     parallel-builds (default: 1)
          The number of builds that may run in parallel on the machine.

     speed (default: 1.0)
          A ``relative speed factor''.  The offload scheduler will tend to prefer machines with a higher speed factor.

     features (default: '())
          A list of strings denoting specific features supported by the machine. An example is "kvm" for machines that have the KVM Linux modules and corresponding hardware support.  Derivations can request features by name, and they will be scheduled on matching build machines.

The guile command must be in the search path on the build machines.  In addition, the Guix modules must be in $GUILE_LOAD_PATH on the build machine---you can check whether this is the case by running:

     ssh build-machine guile -c "'(use-modules (guix config))'"

There is one last thing to do once machines.scm is in place.  As explained above, when offloading, files are transferred back and forth between the machine stores.  For this to work, you first need to generate a key pair on each machine to allow the daemon to export signed archives of files from the store (see Invoking guix archive):

     # guix archive --generate-key

Each build machine must authorize the key of the master machine so that it accepts store items it receives from the master:

     # guix archive --authorize < master-public-key.txt

Likewise, the master machine must authorize the key of each build machine.

All the fuss with keys is here to express pairwise mutual trust relations between the master and the build machines.  Concretely, when the master receives files from a build machine (and vice versa), its build daemon can make sure they are genuine, have not been tampered with, and that they are signed by an authorized key.

To test whether your setup is operational, run this command on the master node:

     # guix offload test

This will attempt to connect to each of the build machines specified in /etc/guix/machines.scm, make sure Guile and the Guix modules are available on each machine, attempt to export to the machine and import from it, and report any error in the process.

If you want to test a different machine file, just specify it on the command line:

     # guix offload test machines-qualif.scm

Last, you can test the subset of the machines whose name matches a regular expression like this:

     # guix offload test machines.scm '\.gnu\.org$'

Invoking guix-daemon
====================

The guix-daemon program implements all the functionality to access the store.  This includes launching build processes, running the garbage collector, querying the availability of a build result, etc.  It is normally run as root like this:

     # guix-daemon --build-users-group=guixbuild

For details on how to set it up, see Setting Up the Daemon.

By default, guix-daemon launches build processes under different UIDs, taken from the build group specified with --build-users-group.  In addition, each build process is run in a chroot environment that only contains the subset of the store that the build process depends on, as specified by its derivation (see derivation), plus a set of specific system directories.  By default, the latter contains /dev and /dev/pts.  Furthermore, on GNU/Linux, the build environment is a container: in addition to having its own file system tree, it has a separate mount name space, its own PID name space, network name space, etc.  This helps achieve reproducible builds (see Features).

When the daemon performs a build on behalf of the user, it creates a build directory under /tmp or under the directory specified by its TMPDIR environment variable; this directory is shared with the container for the duration of the build.  Be aware that using a directory other than /tmp can affect build results---for example, with a longer directory name, a build process that uses Unix-domain sockets might hit the name length limitation for sun_path, which it would otherwise not hit.

The build directory is automatically deleted upon completion, unless the build failed and the client specified --keep-failed (see --keep-failed).

The following command-line options are supported:

--build-users-group=GROUP
     Take users from GROUP to run build processes (see build users).

--no-substitutes
     Do not use substitutes for build products.  That is, always build things locally instead of allowing downloads of pre-built binaries (see Substitutes).

     By default substitutes are used, unless the client---such as the guix package command---is explicitly invoked with --no-substitutes.

     When the daemon runs with --no-substitutes, clients can still explicitly enable substitution via the set-build-options remote procedure call (see The Store).

--substitute-urls=URLS
     Consider URLS the default whitespace-separated list of substitute source URLs.  When this option is omitted, https://mirror.hydra.gnu.org https://hydra.gnu.org is used (mirror.hydra.gnu.org is a mirror of hydra.gnu.org).

     This means that substitutes may be downloaded from URLS, as long as they are signed by a trusted signature (see Substitutes).

--no-build-hook
     Do not use the build hook.

     The build hook is a helper program that the daemon can start and to which it submits build requests.  This mechanism is used to offload builds to other machines (see Daemon Offload Setup).

--cache-failures
     Cache build failures.  By default, only successful builds are cached.

     When this option is used, guix gc --list-failures can be used to query the set of store items marked as failed; guix gc --clear-failures removes store items from the set of cached failures. See Invoking guix gc.

--cores=N
-c N
     Use N CPU cores to build each derivation; 0 means as many as available.

     The default value is 0, but it may be overridden by clients, such as the --cores option of guix build (see Invoking guix build).

     The effect is to define the NIX_BUILD_CORES environment variable in the build process, which can then use it to exploit internal parallelism---for instance, by running make -j$NIX_BUILD_CORES.

--max-jobs=N
-M N
     Allow at most N build jobs in parallel.  The default value is 1.  Setting it to 0 means that no builds will be performed locally; instead, the daemon will offload builds (see Daemon Offload Setup), or simply fail.

--rounds=N
     Build each derivation N times in a row, and raise an error if consecutive build results are not bit-for-bit identical.  Note that this setting can be overridden by clients such as guix build (see Invoking guix build).

     When used in conjunction with --keep-failed, the differing output is kept in the store, under /gnu/store/...-check. This makes it easy to look for differences between the two results.

--debug
     Produce debugging output.

     This is useful to debug daemon start-up issues, but then it may be overridden by clients, for example the --verbosity option of guix build (see Invoking guix build).

--chroot-directory=DIR
     Add DIR to the build chroot.

     Doing this may change the result of build processes---for instance if they use optional dependencies found in DIR when it is available, and not otherwise.  For that reason, it is not recommended to do so. Instead, make sure that each derivation declares all the inputs that it needs.

--disable-chroot
     Disable chroot builds.

     Using this option is not recommended since, again, it would allow build processes to gain access to undeclared dependencies.  It is necessary, though, when guix-daemon is running under an unprivileged user account.

--disable-log-compression
     Disable compression of the build logs.

     Unless --lose-logs is used, all the build logs are kept in the LOCALSTATEDIR.  To save space, the daemon automatically compresses them with bzip2 by default.  This option disables that.

--disable-deduplication
     Disable automatic file ``deduplication'' in the store.

     By default, files added to the store are automatically ``deduplicated'': if a newly added file is identical to another one found in the store, the daemon makes the new file a hard link to the other file.  This can noticeably reduce disk usage, at the expense of slightly increased input/output load at the end of a build process.  This option disables this optimization.

--gc-keep-outputs[=yes|no]
     Tell whether the garbage collector (GC) must keep outputs of live derivations.

     When set to ``yes'', the GC will keep the outputs of any live derivation available in the store---the .drv files.  The default is ``no'', meaning that derivation outputs are kept only if they are GC roots.

--gc-keep-derivations[=yes|no]
     Tell whether the garbage collector (GC) must keep derivations corresponding to live outputs.

     When set to ``yes'', as is the case by default, the GC keeps derivations---i.e., .drv files---as long as at least one of their outputs is live.  This allows users to keep track of the origins of items in their store.  Setting it to ``no'' saves a bit of disk space.

     Note that when both --gc-keep-derivations and --gc-keep-outputs are used, the effect is to keep all the build prerequisites (the sources, compiler, libraries, and other build-time tools) of live objects in the store, regardless of whether these prerequisites are live.  This is convenient for developers since it saves rebuilds or downloads.

--impersonate-linux-2.6
     On Linux-based systems, impersonate Linux 2.6.  This means that the kernel's uname system call will report 2.6 as the release number.

     This might be helpful to build programs that (usually wrongfully) depend on the kernel version number.

--lose-logs
     Do not keep build logs.  By default they are kept under LOCALSTATEDIR/guix/log.

--system=SYSTEM
     Assume SYSTEM as the current system type.  By default it is the architecture/kernel pair found at configure time, such as x86_64-linux.

--listen=SOCKET
     Listen for connections on SOCKET, the file name of a Unix-domain socket.  The default socket is LOCALSTATEDIR/daemon-socket/socket.  This option is only useful in exceptional circumstances, such as if you need to run several daemons on the same machine.

Application Setup
=================

When using Guix on top of GNU/Linux distribution other than GuixSD---a so-called foreign distro---a few additional steps are needed to get everything in place.  Here are some of them.

Locales
-------

Packages installed via Guix will not use the locale data of the host system.  Instead, you must first install one of the locale packages available with Guix and then define the GUIX_LOCPATH environment variable:

     $ guix package -i glibc-locales
     $ export GUIX_LOCPATH=$HOME/.guix-profile/lib/locale

Note that the glibc-locales package contains data for all the locales supported by the GNU libc and weighs in at around 110 MiB.  Alternatively, the glibc-utf8-locales is smaller but limited to a few UTF-8 locales.

The GUIX_LOCPATH variable plays a role similar to LOCPATH (see LOCPATH (The GNU C Library Reference Manual)).  There are two important differences though:

 1. GUIX_LOCPATH is honored only by the libc in Guix, and not by the libc provided by foreign distros.  Thus, using GUIX_LOCPATH allows you to make sure the programs of the foreign distro will not end up loading incompatible locale data.

 2. libc suffixes each entry of GUIX_LOCPATH with /X.Y, where X.Y is the libc version---e.g., 2.22.  This means that, should your Guix profile contain a mixture of programs linked against different libc version, each libc version will only try to load locale data in the right format.

This is important because the locale data format used by different libc versions may be incompatible.

Name Service Switch
-------------------

When using Guix on a foreign distro, we strongly recommend that the system run the GNU C library's name service cache daemon, nscd, which should be listening on the /var/run/nscd/socket socket.  Failing to do that, applications installed with Guix may fail to look up host names or user accounts, or may even crash.  The next paragraphs explain why.

The GNU C library implements a name service switch (NSS), which is an extensible mechanism for ``name lookups'' in general: host name resolution, user accounts, and more (see Name Service Switch (The GNU C Library Reference Manual)).

Being extensible, the NSS supports plugins, which provide new name lookup implementations: for example, the nss-mdns plugin allow resolution of .local host names, the nis plugin allows user account lookup using the Network information service (NIS), and so on.  These extra ``lookup services'' are configured system-wide in /etc/nsswitch.conf, and all the programs running on the system honor those settings (see NSS Configuration File (The GNU C Reference Manual)).

When they perform a name lookup---for instance by calling the getaddrinfo function in C---applications first try to connect to the nscd; on success, nscd performs name lookups on their behalf.  If the nscd is not running, then they perform the name lookup by themselves, by loading the name lookup services into their own address space and running it.  These name lookup services---the libnss_*.so files---are dlopen'd, but they may come from the host system's C library, rather than from the C library the application is linked against (the C library coming from Guix).

And this is where the problem is: if your application is linked against Guix's C library (say, glibc 2.24) and tries to load NSS plugins from another C library (say, libnss_mdns.so for glibc 2.22), it will likely crash or have its name lookups fail unexpectedly.

Running nscd on the system, among other advantages, eliminates this binary incompatibility problem because those libnss_*.so files are loaded in the nscd process, not in applications themselves.

X11 Fonts
---------

The majority of graphical applications use Fontconfig to locate and load fonts and perform X11-client-side rendering.  The fontconfig package in Guix looks for fonts in $HOME/.guix-profile by default.  Thus, to allow graphical applications installed with Guix to display fonts, you have to install fonts with Guix as well. Essential font packages include gs-fonts, font-dejavu, and font-gnu-freefont-ttf.

To display text written in Chinese languages, Japanese, or Korean in graphical applications, consider installing font-adobe-source-han-sans or font-wqy-zenhei.  The former has multiple outputs, one per language family (see Packages with Multiple Outputs).  For instance, the following command installs fonts for Chinese languages:

     guix package -i font-adobe-source-han-sans:cn

Older programs such as xterm do not use Fontconfig and instead rely on server-side font rendering.  Such programs require to specify a full name of a font using XLFD (X Logical Font Description), like this:

     -*-dejavu sans-medium-r-normal-*-*-100-*-*-*-*-*-1

To be able to use such full names for the TrueType fonts installed in your Guix profile, you need to extend the font path of the X server:

     xset +fp ~/.guix-profile/share/fonts/truetype

After that, you can run xlsfonts (from xlsfonts package) to make sure your TrueType fonts are listed there.

X.509 Certificates
------------------

The nss-certs package provides X.509 certificates, which allow programs to authenticate Web servers accessed over HTTPS.

When using Guix on a foreign distro, you can install this package and define the relevant environment variables so that packages know where to look for certificates.  See X.509 Certificates, for detailed information.

Emacs Packages
--------------

When you install Emacs packages with Guix, the elisp files may be placed either in $HOME/.guix-profile/share/emacs/site-lisp/ or in sub-directories of $HOME/.guix-profile/share/emacs/site-lisp/guix.d/.  The latter directory exists because potentially there may exist thousands of Emacs packages and storing all their files in a single directory may be not reliable (because of name conflicts).  So we think using a separate directory for each package is a good idea.  It is very similar to how the Emacs package system organizes the file structure (see Package Files (The GNU Emacs Manual)).

By default, Emacs (installed with Guix) ``knows'' where these packages are placed, so you do not need to perform any configuration.  If, for some reason, you want to avoid auto-loading Emacs packages installed with Guix, you can do so by running Emacs with --no-site-file option (see Init File (The GNU Emacs Manual)).

Package Management
******************

The purpose of GNU Guix is to allow users to easily install, upgrade, and remove software packages, without having to know about their build procedures or dependencies.  Guix also goes beyond this obvious set of features.

This chapter describes the main features of Guix, as well as the package management tools it provides.  Two user interfaces are provided for routine package management tasks: A command-line interface described below (see guix package), as well as a visual user interface in Emacs described in a subsequent chapter (see Emacs Interface).

Features
========

When using Guix, each package ends up in the package store, in its own directory---something that resembles /gnu/store/xxx-package-1.2, where xxx is a base32 string (note that Guix comes with an Emacs extension to shorten those file names, see Emacs Prettify.)

Instead of referring to these directories, users have their own profile, which points to the packages that they actually want to use.  These profiles are stored within each user's home directory, at $HOME/.guix-profile.

For example, alice installs GCC 4.7.2.  As a result, /home/alice/.guix-profile/bin/gcc points to /gnu/store/...-gcc-4.7.2/bin/gcc.  Now, on the same machine, bob had already installed GCC 4.8.0.  The profile of bob simply continues to point to /gnu/store/...-gcc-4.8.0/bin/gcc---i.e., both versions of GCC coexist on the same system without any interference.

The guix package command is the central tool to manage packages (see Invoking guix package).  It operates on the per-user profiles, and can be used with normal user privileges.

The command provides the obvious install, remove, and upgrade operations.  Each invocation is actually a transaction: either the specified operation succeeds, or nothing happens.  Thus, if the guix package process is terminated during the transaction, or if a power outage occurs during the transaction, then the user's profile remains in its previous state, and remains usable.

In addition, any package transaction may be rolled back.  So, if, for example, an upgrade installs a new version of a package that turns out to have a serious bug, users may roll back to the previous instance of their profile, which was known to work well.  Similarly, the global system configuration on GuixSD is subject to transactional upgrades and roll-back (see Using the Configuration System).

All packages in the package store may be garbage-collected. Guix can determine which packages are still referenced by user profiles, and remove those that are provably no longer referenced (see Invoking guix gc).  Users may also explicitly remove old generations of their profile so that the packages they refer to can be collected.

Finally, Guix takes a purely functional approach to package management, as described in the introduction (see Introduction). Each /gnu/store package directory name contains a hash of all the inputs that were used to build that package---compiler, libraries, build scripts, etc.  This direct correspondence allows users to make sure a given package installation matches the current state of their distribution.  It also helps maximize build reproducibility: thanks to the isolated build environments that are used, a given build is likely to yield bit-identical files when performed on different machines (see container).

This foundation allows Guix to support transparent binary/source deployment.  When a pre-built binary for a /gnu/store item is available from an external source---a substitute, Guix just downloads it and unpacks it; otherwise, it builds the package from source, locally (see Substitutes).  Because build results are usually bit-for-bit reproducible, users do not have to trust servers that provide substitutes: they can force a local build and challenge providers (see Invoking guix challenge).

Control over the build environment is a feature that is also useful for developers.  The guix environment command allows developers of a package to quickly set up the right development environment for their package, without having to manually install the dependencies of the package into their profile (see Invoking guix environment).

Invoking guix package
=====================

The guix package command is the tool that allows users to install, upgrade, and remove packages, as well as rolling back to previous configurations.  It operates only on the user's own profile, and works with normal user privileges (see Features).  Its syntax is:

     guix package OPTIONS

Primarily, OPTIONS specifies the operations to be performed during the transaction.  Upon completion, a new profile is created, but previous generations of the profile remain available, should the user want to roll back.

For example, to remove lua and install guile and guile-cairo in a single transaction:

     guix package -r lua -i guile guile-cairo

guix package also supports a declarative approach whereby the user specifies the exact set of packages to be available and passes it via the --manifest option (see --manifest).

For each user, a symlink to the user's default profile is automatically created in $HOME/.guix-profile.  This symlink always points to the current generation of the user's default profile.  Thus, users can add $HOME/.guix-profile/bin to their PATH environment variable, and so on. If you are not using the Guix System Distribution, consider adding the following lines to your ~/.bash_profile (see Bash Startup Files (The GNU Bash Reference Manual)) so that newly-spawned shells get all the right environment variable definitions:

     GUIX_PROFILE="$HOME/.guix-profile" \
     source "$HOME/.guix-profile/etc/profile"

In a multi-user setup, user profiles are stored in a place registered as a garbage-collector root, which $HOME/.guix-profile points to (see Invoking guix gc).  That directory is normally LOCALSTATEDIR/profiles/per-user/USER, where LOCALSTATEDIR is the value passed to configure as --localstatedir, and USER is the user name.  The per-user directory is created when guix-daemon is started, and the USER sub-directory is created by guix package.

The OPTIONS can be among the following:

--install=PACKAGE ...
-i PACKAGE ...
     Install the specified PACKAGEs.

     Each PACKAGE may specify either a simple package name, such as guile, or a package name followed by an at-sign and version number, such as guile@1.8.8 or simply guile@1.8 (in the latter case, the newest version prefixed by 1.8 is selected.)

     If no version number is specified, the newest available version will be selected.  In addition, PACKAGE may contain a colon, followed by the name of one of the outputs of the package, as in gcc:doc or binutils@2.22:lib (see Packages with Multiple Outputs).  Packages with a corresponding name (and optionally version) are searched for among the GNU distribution modules (see Package Modules).

     Sometimes packages have propagated inputs: these are dependencies that automatically get installed along with the required package (see propagated-inputs in package objects, for information about propagated inputs in package definitions).

     An example is the GNU MPC library: its C header files refer to those of the GNU MPFR library, which in turn refer to those of the GMP library. Thus, when installing MPC, the MPFR and GMP libraries also get installed in the profile; removing MPC also removes MPFR and GMP---unless they had also been explicitly installed by the user.

     Besides, packages sometimes rely on the definition of environment variables for their search paths (see explanation of --search-paths below).  Any missing or possibly incorrect environment variable definitions are reported here.

--install-from-expression=EXP
-e EXP
     Install the package EXP evaluates to.

     EXP must be a Scheme expression that evaluates to a <package> object.  This option is notably useful to disambiguate between same-named variants of a package, with expressions such as (@ (gnu packages base) guile-final).

     Note that this option installs the first output of the specified package, which may be insufficient when needing a specific output of a multiple-output package.

--install-from-file=FILE
-f FILE
     Install the package that the code within FILE evaluates to.

     As an example, FILE might contain a definition like this (see Defining Packages):

               [file package-hello.scm not included]

     Developers may find it useful to include such a guix.scm file in the root of their project source tree that can be used to test development snapshots and create reproducible development environments (see Invoking guix environment).

--remove=PACKAGE ...
-r PACKAGE ...
     Remove the specified PACKAGEs.

     As for --install, each PACKAGE may specify a version number and/or output name in addition to the package name.  For instance, -r glibc:debug would remove the debug output of glibc.

--upgrade[=REGEXP ...]
-u [REGEXP ...]
     Upgrade all the installed packages.  If one or more REGEXPs are specified, upgrade only installed packages whose name matches a REGEXP.  Also see the --do-not-upgrade option below.

     Note that this upgrades package to the latest version of packages found in the distribution currently installed.  To update your distribution, you should regularly run guix pull (see Invoking guix pull).

--do-not-upgrade[=REGEXP ...]
     When used together with the --upgrade option, do not upgrade any packages whose name matches a REGEXP.  For example, to upgrade all packages in the current profile except those containing the substring ``emacs'':

          $ guix package --upgrade . --do-not-upgrade emacs

--manifest=FILE
-m FILE
     Create a new generation of the profile from the manifest object returned by the Scheme code in FILE.

     This allows you to declare the profile's contents rather than constructing it through a sequence of --install and similar commands.  The advantage is that FILE can be put under version control, copied to different machines to reproduce the same profile, and so on.

     FILE must return a manifest object, which is roughly a list of packages:

          (use-package-modules guile emacs)

          (packages->manifest
           (list emacs
                 guile-2.0
                 ;; Use a specific package output.
                 (list guile-2.0 "debug")))

--roll-back
     Roll back to the previous generation of the profile---i.e., undo the last transaction.

     When combined with options such as --install, roll back occurs before any other actions.

     When rolling back from the first generation that actually contains installed packages, the profile is made to point to the zeroth generation, which contains no files apart from its own metadata.

     After having rolled back, installing, removing, or upgrading packages overwrites previous future generations.  Thus, the history of the generations in a profile is always linear.

--switch-generation=PATTERN
-S PATTERN
     Switch to a particular generation defined by PATTERN.

     PATTERN may be either a generation number or a number prefixed with ``+'' or ``-''.  The latter means: move forward/backward by a specified number of generations.  For example, if you want to return to the latest generation after --roll-back, use --switch-generation=+1.

     The difference between --roll-back and --switch-generation=-1 is that --switch-generation will not make a zeroth generation, so if a specified generation does not exist, the current generation will not be changed.

--search-paths[=KIND]
     Report environment variable definitions, in Bash syntax, that may be needed in order to use the set of installed packages.  These environment variables are used to specify search paths for files used by some of the installed packages.

     For example, GCC needs the CPATH and LIBRARY_PATH environment variables to be defined so it can look for headers and libraries in the user's profile (see Environment Variables (Using the GNU Compiler Collection (GCC))).  If GCC and, say, the C library are installed in the profile, then --search-paths will suggest setting these variables to PROFILE/include and PROFILE/lib, respectively.

     The typical use case is to define these environment variables in the shell:

          $ eval `guix package --search-paths`

     KIND may be one of exact, prefix, or suffix, meaning that the returned environment variable definitions will either be exact settings, or prefixes or suffixes of the current value of these variables.  When omitted, KIND defaults to exact.

     This option can also be used to compute the combined search paths of several profiles.  Consider this example:

          $ guix package -p foo -i guile
          $ guix package -p bar -i guile-json
          $ guix package -p foo -p bar --search-paths

     The last command above reports about the GUILE_LOAD_PATH variable, even though, taken individually, neither foo nor bar would lead to that recommendation.

--profile=PROFILE
-p PROFILE
     Use PROFILE instead of the user's default profile.

--verbose
     Produce verbose output.  In particular, emit the build log of the environment on the standard error port.

--bootstrap
     Use the bootstrap Guile to build the profile.  This option is only useful to distribution developers.

In addition to these actions, guix package supports the following options to query the current state of a profile, or the availability of packages:

--search=REGEXP
-s REGEXP
     List the available packages whose name, synopsis, or description matches REGEXP.  Print all the metadata of matching packages in recutils format (see GNU recutils databases (GNU recutils manual)).

     This allows specific fields to be extracted using the recsel command, for instance:

          $ guix package -s malloc | recsel -p name,version
          name: glibc
          version: 2.17

          name: libgc
          version: 7.2alpha6

     Similarly, to show the name of all the packages available under the terms of the GNU LGPL version 3:

          $ guix package -s "" | recsel -p name -e 'license ~ "LGPL 3"'
          name: elfutils

          name: gmp
          ...

     It is also possible to refine search results using several -s flags.  For example, the following command returns a list of board games:

          $ guix package -s '\<board\>' -s game | recsel -p name
          name: gnubg
          ...

     If we were to omit -s game, we would also get software packages that deal with printed circuit boards; removing the angle brackets around board would further add packages that have to do with keyboards.

     And now for a more elaborate example.  The following command searches for cryptographic libraries, filters out Haskell, Perl, Python, and Ruby libraries, and prints the name and synopsis of the matching packages:

          $ guix package -s crypto -s library | \
              recsel -e '! (name ~ "^(ghc|perl|python|ruby)")' -p name,synopsis

     See Selection Expressions (GNU recutils manual), for more information on selection expressions for recsel -e.

--show=PACKAGE
     Show details about PACKAGE, taken from the list of available packages, in recutils format (see GNU recutils databases (GNU recutils manual)).

          $ guix package --show=python | recsel -p name,version
          name: python
          version: 2.7.6

          name: python
          version: 3.3.5

     You may also specify the full name of a package to only get details about a specific version of it:

          $ guix package --show=python@3.4 | recsel -p name,version
          name: python
          version: 3.4.3

--list-installed[=REGEXP]
-I [REGEXP]
     List the currently installed packages in the specified profile, with the most recently installed packages shown last.  When REGEXP is specified, list only installed packages whose name matches REGEXP.

     For each installed package, print the following items, separated by tabs: the package name, its version string, the part of the package that is installed (for instance, out for the default output, include for its headers, etc.), and the path of this package in the store.

--list-available[=REGEXP]
-A [REGEXP]
     List packages currently available in the distribution for this system (see GNU Distribution).  When REGEXP is specified, list only installed packages whose name matches REGEXP.

     For each package, print the following items separated by tabs: its name, its version string, the parts of the package (see Packages with Multiple Outputs), and the source location of its definition.

--list-generations[=PATTERN]
-l [PATTERN]
     Return a list of generations along with their creation dates; for each generation, show the installed packages, with the most recently installed packages shown last.  Note that the zeroth generation is never shown.

     For each installed package, print the following items, separated by tabs: the name of a package, its version string, the part of the package that is installed (see Packages with Multiple Outputs), and the location of this package in the store.

     When PATTERN is used, the command returns only matching generations.  Valid patterns include:

       * Integers and comma-separated integers.  Both patterns denote generation numbers.  For instance, --list-generations=1 returns the first one.

          And --list-generations=1,8,2 outputs three generations in the specified order.  Neither spaces nor trailing commas are allowed.

       * Ranges.  --list-generations=2..9 prints the specified generations and everything in between.  Note that the start of a range must be smaller than its end.

          It is also possible to omit the endpoint.  For example, --list-generations=2.., returns all generations starting from the second one.

       * Durations.  You can also get the last N days, weeks, or months by passing an integer along with the first letter of the duration.  For example, --list-generations=20d lists generations that are up to 20 days old.

--delete-generations[=PATTERN]
-d [PATTERN]
     When PATTERN is omitted, delete all generations except the current one.

     This command accepts the same patterns as --list-generations. When PATTERN is specified, delete the matching generations.  When PATTERN specifies a duration, generations older than the specified duration match.  For instance, --delete-generations=1m deletes generations that are more than one month old.

     If the current generation matches, it is not deleted.  Also, the zeroth generation is never deleted.

     Note that deleting generations prevents rolling back to them. Consequently, this command must be used with care.

Finally, since guix package may actually start build processes, it supports all the common build options (see Common Build Options).  It also supports package transformation options, such as --with-source (see Package Transformation Options). However, note that package transformations are lost when upgrading; to preserve transformations across upgrades, you should define your own package variant in a Guile module and add it to GUIX_PACKAGE_PATH (see Defining Packages).

Substitutes
===========

Guix supports transparent source/binary deployment, which means that it can either build things locally, or download pre-built items from a server.  We call these pre-built items substitutes---they are substitutes for local build results.  In many cases, downloading a substitute is much faster than building things locally.

Substitutes can be anything resulting from a derivation build (see Derivations).  Of course, in the common case, they are pre-built package binaries, but source tarballs, for instance, which also result from derivation builds, can be available as substitutes.

The hydra.gnu.org server is a front-end to a build farm that builds packages from the GNU distribution continuously for some architectures, and makes them available as substitutes (see Emacs Hydra, for information on how to query the continuous integration server).  This is the default source of substitutes; it can be overridden by passing the --substitute-urls option either to guix-daemon (see guix-daemon --substitute-urls) or to client tools such as guix package (see client --substitute-urls option).

Substitute URLs can be either HTTP or HTTPS (For HTTPS access, the Guile bindings of GnuTLS must be installed.  See Requirements.) HTTPS is recommended because communications are encrypted; conversely, using HTTP makes all communications visible to an eavesdropper, who could use the information gathered to determine, for instance, whether your system has unpatched security vulnerabilities.

To allow Guix to download substitutes from hydra.gnu.org or a mirror thereof, you must add its public key to the access control list (ACL) of archive imports, using the guix archive command (see Invoking guix archive).  Doing so implies that you trust hydra.gnu.org to not be compromised and to serve genuine substitutes.

This public key is installed along with Guix, in PREFIX/share/guix/hydra.gnu.org.pub, where PREFIX is the installation prefix of Guix.  If you installed Guix from source, make sure you checked the GPG signature of guix-VERSION.tar.gz, which contains this public key file. Then, you can run something like this:

     # guix archive --authorize < hydra.gnu.org.pub

Once this is in place, the output of a command like guix build should change from something like:

     $ guix build emacs --dry-run
     The following derivations would be built:
        /gnu/store/yr7bnx8xwcayd6j95r2clmkdl1qh688w-emacs-24.3.drv
        /gnu/store/x8qsh1hlhgjx6cwsjyvybnfv2i37z23w-dbus-1.6.4.tar.gz.drv
        /gnu/store/1ixwp12fl950d15h2cj11c73733jay0z-alsa-lib-1.0.27.1.tar.bz2.drv
        /gnu/store/nlma1pw0p603fpfiqy7kn4zm105r5dmw-util-linux-2.21.drv
     ...

to something like:

     $ guix build emacs --dry-run
     The following files would be downloaded:
        /gnu/store/pk3n22lbq6ydamyymqkkz7i69wiwjiwi-emacs-24.3
        /gnu/store/2ygn4ncnhrpr61rssa6z0d9x22si0va3-libjpeg-8d
        /gnu/store/71yz6lgx4dazma9dwn2mcjxaah9w77jq-cairo-1.12.16
        /gnu/store/7zdhgp0n1518lvfn8mb96sxqfmvqrl7v-libxrender-0.9.7
     ...

This indicates that substitutes from hydra.gnu.org are usable and will be downloaded, when possible, for future builds.

Guix ignores substitutes that are not signed, or that are not signed by one of the keys listed in the ACL.  It also detects and raises an error when attempting to use a substitute that has been tampered with.

Substitutes are downloaded over HTTP or HTTPS. The http_proxy environment variable can be set in the environment of guix-daemon and is honored for downloads of substitutes.  Note that the value of http_proxy in the environment where guix build, guix package, and other client commands are run has absolutely no effect.

When using HTTPS, the server's X.509 certificate is not validated (in other words, the server is not authenticated), contrary to what HTTPS clients such as Web browsers usually do.  This is because Guix authenticates substitute information itself, as explained above, which is what we care about (whereas X.509 certificates are about authenticating bindings between domain names and public keys.)

The substitute mechanism can be disabled globally by running guix-daemon with --no-substitutes (see Invoking guix-daemon).  It can also be disabled temporarily by passing the --no-substitutes option to guix package, guix build, and other command-line tools.

On Trusting Binaries
--------------------

Today, each individual's control over their own computing is at the mercy of institutions, corporations, and groups with enough power and determination to subvert the computing infrastructure and exploit its weaknesses.  While using hydra.gnu.org substitutes can be convenient, we encourage users to also build on their own, or even run their own build farm, such that hydra.gnu.org is less of an interesting target.  One way to help is by publishing the software you build using guix publish so that others have one more choice of server to download substitutes from (see Invoking guix publish).

Guix has the foundations to maximize build reproducibility (see Features).  In most cases, independent builds of a given package or derivation should yield bit-identical results.  Thus, through a diverse set of independent package builds, we can strengthen the integrity of our systems.  The guix challenge command aims to help users assess substitute servers, and to assist developers in finding out about non-deterministic package builds (see Invoking guix challenge).  Similarly, the --check option of guix build allows users to check whether previously-installed substitutes are genuine by rebuilding them locally (see guix build --check).

In the future, we want Guix to have support to publish and retrieve binaries to/from other users, in a peer-to-peer fashion.  If you would like to discuss this project, join us on guix-devel@gnu.org.

Packages with Multiple Outputs
==============================

Often, packages defined in Guix have a single output---i.e., the source package leads to exactly one directory in the store.  When running guix package -i glibc, one installs the default output of the GNU libc package; the default output is called out, but its name can be omitted as shown in this command.  In this particular case, the default output of glibc contains all the C header files, shared libraries, static libraries, Info documentation, and other supporting files.

Sometimes it is more appropriate to separate the various types of files produced from a single source package into separate outputs.  For instance, the GLib C library (used by GTK+ and related packages) installs more than 20 MiB of reference documentation as HTML pages. To save space for users who do not need it, the documentation goes to a separate output, called doc.  To install the main GLib output, which contains everything but the documentation, one would run:

     guix package -i glib

The command to install its documentation is:

     guix package -i glib:doc

Some packages install programs with different ``dependency footprints''. For instance, the WordNet package installs both command-line tools and graphical user interfaces (GUIs).  The former depend solely on the C library, whereas the latter depend on Tcl/Tk and the underlying X libraries.  In this case, we leave the command-line tools in the default output, whereas the GUIs are in a separate output.  This allows users who do not need the GUIs to save space.  The guix size command can help find out about such situations (see Invoking guix size). guix graph can also be helpful (see Invoking guix graph).

There are several such multiple-output packages in the GNU distribution. Other conventional output names include lib for libraries and possibly header files, bin for stand-alone programs, and debug for debugging information (see Installing Debugging Files).  The outputs of a packages are listed in the third column of the output of guix package --list-available (see Invoking guix package).

Invoking guix gc
================

Packages that are installed, but not used, may be garbage-collected. The guix gc command allows users to explicitly run the garbage collector to reclaim space from the /gnu/store directory.  It is the only way to remove files from /gnu/store---removing files or directories manually may break it beyond repair!

The garbage collector has a set of known roots: any file under /gnu/store reachable from a root is considered live and cannot be deleted; any other file is considered dead and may be deleted.  The set of garbage collector roots includes default user profiles, and may be augmented with guix build --root, for example (see Invoking guix build).

Prior to running guix gc --collect-garbage to make space, it is often useful to remove old generations from user profiles; that way, old package builds referenced by those generations can be reclaimed.  This is achieved by running guix package --delete-generations (see Invoking guix package).

The guix gc command has three modes of operation: it can be used to garbage-collect any dead files (the default), to delete specific files (the --delete option), to print garbage-collector information, or for more advanced queries.  The garbage collection options are as follows:

--collect-garbage[=MIN]
-C [MIN]
     Collect garbage---i.e., unreachable /gnu/store files and sub-directories.  This is the default operation when no option is specified.

     When MIN is given, stop once MIN bytes have been collected. MIN may be a number of bytes, or it may include a unit as a suffix, such as MiB for mebibytes and GB for gigabytes (see size specifications (GNU Coreutils)).

     When MIN is omitted, collect all the garbage.

--free-space=FREE
-F FREE
     Collect garbage until FREE space is available under /gnu/store, if possible; FREE denotes storage space, such as 500MiB, as described above.

     When FREE or more is already available in /gnu/store, do nothing and exit immediately.

--delete
-d
     Attempt to delete all the store files and directories specified as arguments.  This fails if some of the files are not in the store, or if they are still live.

--list-failures
     List store items corresponding to cached build failures.

     This prints nothing unless the daemon was started with --cache-failures (see --cache-failures).

--clear-failures
     Remove the specified store items from the failed-build cache.

     Again, this option only makes sense when the daemon is started with --cache-failures.  Otherwise, it does nothing.

--list-dead
     Show the list of dead files and directories still present in the store---i.e., files and directories no longer reachable from any root.

--list-live
     Show the list of live store files and directories.

In addition, the references among existing store files can be queried:

--references
--referrers
     List the references (respectively, the referrers) of store files given as arguments.

--requisites
-R
     List the requisites of the store files passed as arguments.  Requisites include the store files themselves, their references, and the references of these, recursively.  In other words, the returned list is the transitive closure of the store files.

     See Invoking guix size, for a tool to profile the size of the closure of an element.  See Invoking guix graph, for a tool to visualize the graph of references.

Lastly, the following options allow you to check the integrity of the store and to control disk usage.

--verify[=OPTIONS]
     Verify the integrity of the store.

     By default, make sure that all the store items marked as valid in the database of the daemon actually exist in /gnu/store.

     When provided, OPTIONS must be a comma-separated list containing one or more of contents and repair.

     When passing --verify=contents, the daemon computes the content hash of each store item and compares it against its hash in the database.  Hash mismatches are reported as data corruptions.  Because it traverses all the files in the store, this command can take a long time, especially on systems with a slow disk drive.

     Using --verify=repair or --verify=contents,repair causes the daemon to try to repair corrupt store items by fetching substitutes for them (see Substitutes).  Because repairing is not atomic, and thus potentially dangerous, it is available only to the system administrator.

--optimize
     Optimize the store by hard-linking identical files---this is deduplication.

     The daemon performs deduplication after each successful build or archive import, unless it was started with --disable-deduplication (see --disable-deduplication).  Thus, this option is primarily useful when the daemon was running with --disable-deduplication.

Invoking guix pull
==================

Packages are installed or upgraded to the latest version available in the distribution currently available on your local machine.  To update that distribution, along with the Guix tools, you must run guix pull: the command downloads the latest Guix source code and package descriptions, and deploys it.

On completion, guix package will use packages and package versions from this just-retrieved copy of Guix.  Not only that, but all the Guix commands and Scheme modules will also be taken from that latest version.  New guix sub-commands added by the update also become available.

Any user can update their Guix copy using guix pull, and the effect is limited to the user who run guix pull.  For instance, when user root runs guix pull, this has no effect on the version of Guix that user alice sees, and vice versa (Under the hood, guix pull updates the ~/.config/guix/latest symbolic link to point to the latest Guix, and the guix command loads code from there.).

The guix pull command is usually invoked with no arguments, but it supports the following options:

--verbose
     Produce verbose output, writing build logs to the standard error output.

--url=URL
     Download the source tarball of Guix from URL.

     By default, the tarball is taken from its canonical address at gnu.org, for the stable branch of Guix.

--bootstrap
     Use the bootstrap Guile to build the latest Guix.  This option is only useful to Guix developers.

Invoking guix archive
=====================

The guix archive command allows users to export files from the store into a single archive, and to later import them. In particular, it allows store files to be transferred from one machine to the store on another machine.

To export store files as an archive to standard output, run:

     guix archive --export OPTIONS SPECIFICATIONS...

SPECIFICATIONS may be either store file names or package specifications, as for guix package (see Invoking guix package).  For instance, the following command creates an archive containing the gui output of the git package and the main output of emacs:

     guix archive --export git:gui /gnu/store/...-emacs-24.3 > great.nar

If the specified packages are not built yet, guix archive automatically builds them.  The build process may be controlled with the common build options (see Common Build Options).

To transfer the emacs package to a machine connected over SSH, one would run:

     guix archive --export -r emacs | ssh the-machine guix archive --import

Similarly, a complete user profile may be transferred from one machine to another like this:

     guix archive --export -r $(readlink -f ~/.guix-profile) | \
       ssh the-machine guix-archive --import

However, note that, in both examples, all of emacs and the profile as well as all of their dependencies are transferred (due to -r), regardless of what is already available in the store on the target machine.  The --missing option can help figure out which items are missing from the target store.

Archives are stored in the ``normalized archive'' or ``nar'' format, which is comparable in spirit to `tar', but with differences that make it more appropriate for our purposes.  First, rather than recording all Unix metadata for each file, the nar format only mentions the file type (regular, directory, or symbolic link); Unix permissions and owner/group are dismissed.  Second, the order in which directory entries are stored always follows the order of file names according to the C locale collation order.  This makes archive production fully deterministic.

When exporting, the daemon digitally signs the contents of the archive, and that digital signature is appended.  When importing, the daemon verifies the signature and rejects the import in case of an invalid signature or if the signing key is not authorized.

The main options are:

--export
     Export the specified store files or packages (see below.)  Write the resulting archive to the standard output.

     Dependencies are not included in the output, unless --recursive is passed.

-r
--recursive
     When combined with --export, this instructs guix archive to include dependencies of the given items in the archive. Thus, the resulting archive is self-contained: it contains the closure of the exported store items.

--import
     Read an archive from the standard input, and import the files listed therein into the store.  Abort if the archive has an invalid digital signature, or if it is signed by a public key not among the authorized keys (see --authorize below.)

--missing
     Read a list of store file names from the standard input, one per line, and write on the standard output the subset of these files missing from the store.

--generate-key[=PARAMETERS]
     Generate a new key pair for the daemon.  This is a prerequisite before archives can be exported with --export.  Note that this operation usually takes time, because it needs to gather enough entropy to generate the key pair.

     The generated key pair is typically stored under /etc/guix, in signing-key.pub (public key) and signing-key.sec (private key, which must be kept secret.)  When PARAMETERS is omitted, an ECDSA key using the Ed25519 curve is generated, or, for Libgcrypt versions before 1.6.0, it is a 4096-bit RSA key. Alternatively, PARAMETERS can specify genkey parameters suitable for Libgcrypt (see gcry_pk_genkey (The Libgcrypt Reference Manual)).

--authorize
     Authorize imports signed by the public key passed on standard input. The public key must be in ``s-expression advanced format''---i.e., the same format as the signing-key.pub file.

     The list of authorized keys is kept in the human-editable file /etc/guix/acl.  The file contains ``advanced-format s-expressions'' (http://people.csail.mit.edu/rivest/Sexp.txt) and is structured as an access-control list in the Simple Public-Key Infrastructure (SPKI) (http://theworld.com/~cme/spki.txt).

--extract=DIRECTORY
-x DIRECTORY
     Read a single-item archive as served by substitute servers (see Substitutes) and extract it to DIRECTORY.  This is a low-level operation needed in only very narrow use cases; see below.

     For example, the following command extracts the substitute for Emacs served by hydra.gnu.org to /tmp/emacs:

          $ wget -O - \
            https://hydra.gnu.org/nar/...-emacs-24.5 \
            | bunzip2 | guix archive -x /tmp/emacs

     Single-item archives are different from multiple-item archives produced by guix archive --export; they contain a single store item, and they do not embed a signature.  Thus this operation does no signature verification and its output should be considered unsafe.

     The primary purpose of this operation is to facilitate inspection of archive contents coming from possibly untrusted substitute servers.

     [file emacs.texi not included]

Programming Interface
*********************

GNU Guix provides several Scheme programming interfaces (APIs) to define, build, and query packages.  The first interface allows users to write high-level package definitions.  These definitions refer to familiar packaging concepts, such as the name and version of a package, its build system, and its dependencies.  These definitions can then be turned into concrete build actions.

Build actions are performed by the Guix daemon, on behalf of users.  In a standard setup, the daemon has write access to the store---the /gnu/store directory---whereas users do not.  The recommended setup also has the daemon perform builds in chroots, under a specific build users, to minimize interference with the rest of the system.

Lower-level APIs are available to interact with the daemon and the store.  To instruct the daemon to perform a build action, users actually provide it with a derivation.  A derivation is a low-level representation of the build actions to be taken, and the environment in which they should occur---derivations are to package definitions what assembly is to C programs.  The term ``derivation'' comes from the fact that build results derive from them.

This chapter describes all these APIs in turn, starting from high-level package definitions.

Defining Packages
=================

The high-level interface to package definitions is implemented in the (guix packages) and (guix build-system) modules.  As an example, the package definition, or recipe, for the GNU Hello package looks like this:

     (define-module (gnu packages hello)
       #:use-module (guix packages)
       #:use-module (guix download)
       #:use-module (guix build-system gnu)
       #:use-module (guix licenses)
       #:use-module (gnu packages gawk))

     (define-public hello
       (package
         (name "hello")
         (version "2.10")
         (source (origin
                   (method url-fetch)
                   (uri (string-append "mirror://gnu/hello/hello-" version
                                       ".tar.gz"))
                   (sha256
                    (base32
                     "0ssi1wpaf7plaswqqjwigppsg5fyh99vdlb9kzl7c9lng89ndq1i"))))
         (build-system gnu-build-system)
         (arguments '(#:configure-flags '("--enable-silent-rules")))
         (inputs `(("gawk" ,gawk)))
         (synopsis "Hello, GNU world: An example GNU package")
         (description "Guess what GNU Hello prints!")
         (home-page "http://www.gnu.org/software/hello/")
         (license gpl3+)))

Without being a Scheme expert, the reader may have guessed the meaning of the various fields here.  This expression binds the variable hello to a <package> object, which is essentially a record (see Scheme records (GNU Guile Reference Manual)). This package object can be inspected using procedures found in the (guix packages) module; for instance, (package-name hello) returns---surprise!---"hello".

With luck, you may be able to import part or all of the definition of the package you are interested in from another repository, using the guix import command (see Invoking guix import).

In the example above, HELLO is defined in a module of its own, (gnu packages hello).  Technically, this is not strictly necessary, but it is convenient to do so: all the packages defined in modules under (gnu packages ...) are automatically known to the command-line tools (see Package Modules).

There are a few points worth noting in the above package definition:

  * The source field of the package is an <origin> object (see origin Reference, for the complete reference). Here, the url-fetch method from (guix download) is used, meaning that the source is a file to be downloaded over FTP or HTTP.

     The mirror://gnu prefix instructs url-fetch to use one of the GNU mirrors defined in (guix download).

     The sha256 field specifies the expected SHA256 hash of the file being downloaded.  It is mandatory, and allows Guix to check the integrity of the file.  The (base32 ...) form introduces the base32 representation of the hash.  You can obtain this information with guix download (see Invoking guix download) and guix hash (see Invoking guix hash).

     When needed, the origin form can also have a patches field listing patches to be applied, and a snippet field giving a Scheme expression to modify the source code.

  * The build-system field specifies the procedure to build the package (see Build Systems).  Here, GNU-BUILD-SYSTEM represents the familiar GNU Build System, where packages may be configured, built, and installed with the usual ./configure && make && make check && make install command sequence.

  * The arguments field specifies options for the build system (see Build Systems).  Here it is interpreted by GNU-BUILD-SYSTEM as a request run configure with the --enable-silent-rules flag.

     What about these quote (') characters?  They are Scheme syntax to introduce a literal list; ' is synonymous with quote. See quoting (GNU Guile Reference Manual), for details.  Here the value of the arguments field is a list of arguments passed to the build system down the road, as with apply (see apply (GNU Guile Reference Manual)).

     The hash-colon (#:) sequence defines a Scheme keyword (see Keywords (GNU Guile Reference Manual)), and #:configure-flags is a keyword used to pass a keyword argument to the build system (see Coding With Keywords (GNU Guile Reference Manual)).

  * The inputs field specifies inputs to the build process---i.e., build-time or run-time dependencies of the package.  Here, we define an input called "gawk" whose value is that of the GAWK variable; GAWK is itself bound to a <package> object.

     Again, ` (a backquote, synonymous with quasiquote) allows us to introduce a literal list in the inputs field, while , (a comma, synonymous with unquote) allows us to insert a value in that list (see unquote (GNU Guile Reference Manual)).

     Note that GCC, Coreutils, Bash, and other essential tools do not need to be specified as inputs here.  Instead, GNU-BUILD-SYSTEM takes care of ensuring that they are present (see Build Systems).

     However, any other dependencies need to be specified in the inputs field.  Any dependency not specified here will simply be unavailable to the build process, possibly leading to a build failure.

See package Reference, for a full description of possible fields.

Once a package definition is in place, the package may actually be built using the guix build command-line tool (see Invoking guix build).  You can easily jump back to the package definition using the guix edit command (see Invoking guix edit). See Packaging Guidelines, for more information on how to test package definitions, and Invoking guix lint, for information on how to check a definition for style conformance.

Finally, updating the package definition to a new upstream version can be partly automated by the guix refresh command (see Invoking guix refresh).

Behind the scenes, a derivation corresponding to the <package> object is first computed by the package-derivation procedure. That derivation is stored in a .drv file under /gnu/store. The build actions it prescribes may then be realized by using the build-derivations procedure (see The Store).

 -- Scheme Procedure: package-derivation STORE PACKAGE [SYSTEM]
     Return the <derivation> object of PACKAGE for SYSTEM (see Derivations).

     PACKAGE must be a valid <package> object, and SYSTEM must be a string denoting the target system type---e.g., "x86_64-linux" for an x86_64 Linux-based GNU system.  STORE must be a connection to the daemon, which operates on the store (see The Store).

Similarly, it is possible to compute a derivation that cross-builds a package for some other system:

 -- Scheme Procedure: package-cross-derivation STORE
     PACKAGE TARGET [SYSTEM]
     Return the <derivation> object of PACKAGE cross-built from SYSTEM to TARGET.

     TARGET must be a valid GNU triplet denoting the target hardware and operating system, such as "mips64el-linux-gnu" (see GNU configuration triplets (GNU Configure and Build System)).

Packages can be manipulated in arbitrary ways.  An example of a useful transformation is input rewriting, whereby the dependency tree of a package is rewritten by replacing specific inputs by others:

 -- Scheme Procedure: package-input-rewriting REPLACEMENTS
     [REWRITE-NAME]
     Return a procedure that, when passed a package, replaces its direct and indirect dependencies (but not its implicit inputs) according to REPLACEMENTS.  REPLACEMENTS is a list of package pairs; the first element of each pair is the package to replace, and the second one is the replacement.

     Optionally, REWRITE-NAME is a one-argument procedure that takes the name of a package and returns its new name after rewrite.

Consider this example:

     (define libressl-instead-of-openssl
       ;; This is a procedure to replace OPENSSL by LIBRESSL,
       ;; recursively.
       (package-input-rewriting `((,openssl . ,libressl))))

     (define git-with-libressl
       (libressl-instead-of-openssl git))

Here we first define a rewriting procedure that replaces OPENSSL with LIBRESSL.  Then we use it to define a variant of the GIT package that uses LIBRESSL instead of OPENSSL. This is exactly what the --with-input command-line option does (see --with-input).

package Reference
-----------------

This section summarizes all the options available in package declarations (see Defining Packages).

 -- Data Type: package
     This is the data type representing a package recipe.

     name
          The name of the package, as a string.

     version
          The version of the package, as a string.

     source
          An object telling how the source code for the package should be acquired.  Most of the time, this is an origin object, which denotes a file fetched from the Internet (see origin Reference).  It can also be any other ``file-like'' object such as a local-file, which denotes a file from the local file system (see local-file).

     build-system
          The build system that should be used to build the package (see Build Systems).

     arguments (default: '())
          The arguments that should be passed to the build system.  This is a list, typically containing sequential keyword-value pairs.

     inputs (default: '())
     native-inputs (default: '())
     propagated-inputs (default: '())
          These fields list dependencies of the package.  Each one is a list of tuples, where each tuple has a label for the input (a string) as its first element, a package, origin, or derivation as its second element, and optionally the name of the output thereof that should be used, which defaults to "out" (see Packages with Multiple Outputs, for more on package outputs).  For example, the list below specifies three inputs:

               `(("libffi" ,libffi)
                 ("libunistring" ,libunistring)
                 ("glib:bin" ,glib "bin"))  ;the "bin" output of Glib

          The distinction between native-inputs and inputs is necessary when considering cross-compilation.  When cross-compiling, dependencies listed in inputs are built for the target architecture; conversely, dependencies listed in native-inputs are built for the architecture of the build machine.

          native-inputs is typically used to list tools needed at build time, but not at run time, such as Autoconf, Automake, pkg-config, Gettext, or Bison.  guix lint can report likely mistakes in this area (see Invoking guix lint).

          Lastly, propagated-inputs is similar to inputs, but the specified packages will be automatically installed alongside the package they belong to (see guix package, for information on how guix package deals with propagated inputs.)

          For example this is necessary when a C/C++ library needs headers of another library to compile, or when a pkg-config file refers to another one via its Requires field.

          Another example where propagated-inputs is useful is for languages that lack a facility to record the run-time search path akin to the RUNPATH of ELF files; this includes Guile, Python, Perl, and more.  To ensure that libraries written in those languages can find library code they depend on at run time, run-time dependencies must be listed in propagated-inputs rather than inputs.

     self-native-input? (default: #f)
          This is a Boolean field telling whether the package should use itself as a native input when cross-compiling.

     outputs (default: '("out"))
          The list of output names of the package.  See Packages with Multiple Outputs, for typical uses of additional outputs.

     native-search-paths (default: '())
     search-paths (default: '())
          A list of search-path-specification objects describing search-path environment variables honored by the package.

     replacement (default: #f)
          This must be either #f or a package object that will be used as a replacement for this package.  See grafts, for details.

     synopsis
          A one-line description of the package.

     description
          A more elaborate description of the package.

     license
          The license of the package; a value from (guix licenses), or a list of such values.

     home-page
          The URL to the home-page of the package, as a string.

     supported-systems (default: %SUPPORTED-SYSTEMS)
          The list of systems supported by the package, as strings of the form architecture-kernel, for example "x86_64-linux".

     maintainers (default: '())
          The list of maintainers of the package, as maintainer objects.

     location (default: source location of the package form)
          The source location of the package.  It is useful to override this when inheriting from another package, in which case this field is not automatically corrected.

origin Reference
----------------

This section summarizes all the options available in origin declarations (see Defining Packages).

 -- Data Type: origin
     This is the data type representing a source code origin.

     uri
          An object containing the URI of the source.  The object type depends on the method (see below).  For example, when using the URL-FETCH method of (guix download), the valid uri values are: a URL represented as a string, or a list thereof.

     method
          A procedure that handles the URI.

          Examples include:

          URL-FETCH from (guix download)
               download a file from the HTTP, HTTPS, or FTP URL specified in the uri field;

          GIT-FETCH from (guix git-download)
               clone the Git version control repository, and check out the revision specified in the uri field as a git-reference object; a git-reference looks like this:

                    (git-reference
                      (url "git://git.debian.org/git/pkg-shadow/shadow")
                      (commit "v4.1.5.1"))

     sha256
          A bytevector containing the SHA-256 hash of the source.  Typically the base32 form is used here to generate the bytevector from a base-32 string.

          You can obtain this information using guix download (see Invoking guix download) or guix hash (see Invoking guix hash).

     file-name (default: #f)
          The file name under which the source code should be saved.  When this is #f, a sensible default value will be used in most cases.  In case the source is fetched from a URL, the file name from the URL will be used.  For version control checkouts, it is recommended to provide the file name explicitly because the default is not very descriptive.

     patches (default: '())
          A list of file names containing patches to be applied to the source.

          This list of patches must be unconditional.  In particular, it cannot depend on the value of %current-system or %current-target-system.

     snippet (default: #f)
          A G-expression (see G-Expressions) or S-expression that will be run in the source directory.  This is a convenient way to modify the source, sometimes more convenient than a patch.

     patch-flags (default: '("-p1"))
          A list of command-line flags that should be passed to the patch command.

     patch-inputs (default: #f)
          Input packages or derivations to the patching process.  When this is #f, the usual set of inputs necessary for patching are provided, such as GNU Patch.

     modules (default: '())
          A list of Guile modules that should be loaded during the patching process and while running the code in the snippet field.

     patch-guile (default: #f)
          The Guile package that should be used in the patching process.  When this is #f, a sensible default is used.

Build Systems
=============

Each package definition specifies a build system and arguments for that build system (see Defining Packages).  This build-system field represents the build procedure of the package, as well as implicit dependencies of that build procedure.

Build systems are <build-system> objects.  The interface to create and manipulate them is provided by the (guix build-system) module, and actual build systems are exported by specific modules.

Under the hood, build systems first compile package objects to bags.  A bag is like a package, but with less ornamentation---in other words, a bag is a lower-level representation of a package, which includes all the inputs of that package, including some that were implicitly added by the build system.  This intermediate representation is then compiled to a derivation (see Derivations).

Build systems accept an optional list of arguments.  In package definitions, these are passed via the arguments field (see Defining Packages).  They are typically keyword arguments (see keyword arguments in Guile (GNU Guile Reference Manual)).  The value of these arguments is usually evaluated in the build stratum---i.e., by a Guile process launched by the daemon (see Derivations).

The main build system is GNU-BUILD-SYSTEM, which implements the standard build procedure for GNU and many other packages.  It is provided by the (guix build-system gnu) module.

 -- Scheme Variable: gnu-build-system
     GNU-BUILD-SYSTEM represents the GNU Build System, and variants thereof (see configuration and makefile conventions (GNU Coding Standards)).

     In a nutshell, packages using it are configured, built, and installed with the usual ./configure && make && make check && make install command sequence.  In practice, a few additional steps are often needed. All these steps are split up in separate phases, notably (Please see the (guix build gnu-build-system) modules for more details about the build phases.):

     unpack
          Unpack the source tarball, and change the current directory to the extracted source tree.  If the source is actually a directory, copy it to the build tree, and enter that directory.

     patch-source-shebangs
          Patch shebangs encountered in source files so they refer to the right store file names.  For instance, this changes #!/bin/sh to #!/gnu/store/...-bash-4.3/bin/sh.

     configure
          Run the configure script with a number of default options, such as --prefix=/gnu/store/..., as well as the options specified by the #:configure-flags argument.

     build
          Run make with the list of flags specified with #:make-flags.  If the #:parallel-build? argument is true (the default), build with make -j.

     check
          Run make check, or some other target specified with #:test-target, unless #:tests? #f is passed.  If the #:parallel-tests? argument is true (the default), run make check -j.

     install
          Run make install with the flags listed in #:make-flags.

     patch-shebangs
          Patch shebangs on the installed executable files.

     strip
          Strip debugging symbols from ELF files (unless #:strip-binaries? is false), copying them to the debug output when available (see Installing Debugging Files).

     The build-side module (guix build gnu-build-system) defines %STANDARD-PHASES as the default list of build phases. %STANDARD-PHASES is a list of symbol/procedure pairs, where the procedure implements the actual phase.

     The list of phases used for a particular package can be changed with the #:phases parameter.  For instance, passing:

          #:phases (modify-phases %standard-phases (delete 'configure))

     means that all the phases described above will be used, except the configure phase.

     In addition, this build system ensures that the ``standard'' environment for GNU packages is available.  This includes tools such as GCC, libc, Coreutils, Bash, Make, Diffutils, grep, and sed (see the (guix build-system gnu) module for a complete list).  We call these the implicit inputs of a package, because package definitions do not have to mention them.

Other <build-system> objects are defined to support other conventions and tools used by free software packages.  They inherit most of GNU-BUILD-SYSTEM, and differ mainly in the set of inputs implicitly added to the build process, and in the list of phases executed.  Some of these build systems are listed below.

 -- Scheme Variable: ant-build-system
     This variable is exported by (guix build-system ant).  It implements the build procedure for Java packages that can be built with Ant build tool (http://ant.apache.org/).

     It adds both ant and the Java Development Kit (JDK) as provided by the icedtea package to the set of inputs.  Different packages can be specified with the #:ant and #:jdk parameters, respectively.

     When the original package does not provide a suitable Ant build file, the parameter #:jar-name can be used to generate a minimal Ant build file build.xml with tasks to build the specified jar archive.

     The parameter #:build-target can be used to specify the Ant task that should be run during the build phase.  By default the ``jar'' task will be run.

 -- Scheme Variable: asdf-build-system/source
 -- Scheme Variable: asdf-build-system/sbcl
 -- Scheme Variable: asdf-build-system/ecl

     These variables, exported by (guix build-system asdf), implement build procedures for Common Lisp packages using ``ASDF'' (https://common-lisp.net/project/asdf/). ASDF is a system definition facility for Common Lisp programs and libraries.

     The asdf-build-system/source system installs the packages in source form, and can be loaded using any common lisp implementation, via ASDF.  The others, such as asdf-build-system/sbcl, install binary systems in the format which a particular implementation understands. These build systems can also be used to produce executable programs, or lisp images which contain a set of packages pre-loaded.

     The build system uses naming conventions.  For binary packages, the package itself as well as its run-time dependencies should begin their name with the lisp implementation, such as sbcl- for asdf-build-system/sbcl.  Beginning the input name with this prefix will allow the build system to encode its location into the resulting library, so that the input can be found at run-time.

     If dependencies are used only for tests, it is convenient to use a different prefix in order to avoid having a run-time dependency on such systems.  For example,

          (define-public sbcl-bordeaux-threads
            (package
              ...
              (native-inputs `(("tests:cl-fiveam" ,sbcl-fiveam)))
              ...))

     Additionally, the corresponding source package should be labeled using the same convention as python packages (see Python Modules), using the cl- prefix.

     For binary packages, each system should be defined as a Guix package. If one package origin contains several systems, package variants can be created in order to build all the systems.  Source packages, which use asdf-build-system/source, may contain several systems.

     In order to create executable programs and images, the build-side procedures build-program and build-image can be used. They should be called in a build phase after the create-symlinks phase, so that the system which was just built can be used within the resulting image.  build-program requires a list of Common Lisp expressions to be passed as the #:entry-program argument.

     If the system is not defined within its own .asd file of the same name, then the #:asd-file parameter should be used to specify which file the system is defined in.

 -- Scheme Variable: cargo-build-system
     This variable is exported by (guix build-system cargo).  It supports builds of packages using Cargo, the build tool of the Rust programming language (https://www.rust-lang.org).

     In its configure phase, this build system replaces dependencies specified in the Carto.toml file with inputs to the Guix package. The install phase installs the binaries, and it also installs the source code and Cargo.toml file.

 -- Scheme Variable: cmake-build-system
     This variable is exported by (guix build-system cmake).  It implements the build procedure for packages using the CMake build tool (http://www.cmake.org).

     It automatically adds the cmake package to the set of inputs. Which package is used can be specified with the #:cmake parameter.

     The #:configure-flags parameter is taken as a list of flags passed to the cmake command.  The #:build-type parameter specifies in abstract terms the flags passed to the compiler; it defaults to "RelWithDebInfo" (short for ``release mode with debugging information''), which roughly means that code is compiled with -O2 -g, as is the case for Autoconf-based packages by default.

 -- Scheme Variable: glib-or-gtk-build-system
     This variable is exported by (guix build-system glib-or-gtk).  It is intended for use with packages making use of GLib or GTK+.

     This build system adds the following two phases to the ones defined by GNU-BUILD-SYSTEM:

     glib-or-gtk-wrap
          The phase glib-or-gtk-wrap ensures that programs in bin/ are able to find GLib ``schemas'' and GTK+ modules (https://developer.gnome.org/gtk3/stable/gtk-running.html).  This is achieved by wrapping the programs in launch scripts that appropriately set the XDG_DATA_DIRS and GTK_PATH environment variables.

          It is possible to exclude specific package outputs from that wrapping process by listing their names in the #:glib-or-gtk-wrap-excluded-outputs parameter.  This is useful when an output is known not to contain any GLib or GTK+ binaries, and where wrapping would gratuitously add a dependency of that output on GLib and GTK+.

     glib-or-gtk-compile-schemas
          The phase glib-or-gtk-compile-schemas makes sure that all GSettings schemas (https://developer.gnome.org/gio/stable/glib-compile-schemas.html) of GLib are compiled.  Compilation is performed by the glib-compile-schemas program.  It is provided by the package glib:bin which is automatically imported by the build system. The glib package providing glib-compile-schemas can be specified with the #:glib parameter.

     Both phases are executed after the install phase.

 -- Scheme Variable: python-build-system
     This variable is exported by (guix build-system python).  It implements the more or less standard build procedure used by Python packages, which consists in running python setup.py build and then python setup.py install --prefix=/gnu/store/....

     For packages that install stand-alone Python programs under bin/, it takes care of wrapping these programs so that their PYTHONPATH environment variable points to all the Python libraries they depend on.

     Which Python package is used to perform the build can be specified with the #:python parameter.  This is a useful way to force a package to be built for a specific version of the Python interpreter, which might be necessary if the package is only compatible with a single interpreter version.

     By default guix calls setup.py under control of setuptools, much like pip does.  Some packages are not compatible with setuptools (and pip), thus you can disable this by setting the #:use-setuptools parameter to #f.

 -- Scheme Variable: perl-build-system
     This variable is exported by (guix build-system perl).  It implements the standard build procedure for Perl packages, which either consists in running perl Build.PL --prefix=/gnu/store/..., followed by Build and Build install; or in running perl Makefile.PL PREFIX=/gnu/store/..., followed by make and make install, depending on which of Build.PL or Makefile.PL is present in the package distribution.  Preference is given to the former if both Build.PL and Makefile.PL exist in the package distribution.  This preference can be reversed by specifying #t for the #:make-maker? parameter.

     The initial perl Makefile.PL or perl Build.PL invocation passes flags specified by the #:make-maker-flags or #:module-build-flags parameter, respectively.

     Which Perl package is used can be specified with #:perl.

 -- Scheme Variable: r-build-system
     This variable is exported by (guix build-system r).  It implements the build procedure used by R (http://r-project.org) packages, which essentially is little more than running R CMD INSTALL --library=/gnu/store/... in an environment where R_LIBS_SITE contains the paths to all R package inputs.  Tests are run after installation using the R function tools::testInstalledPackage.

 -- Scheme Variable: ruby-build-system
     This variable is exported by (guix build-system ruby).  It implements the RubyGems build procedure used by Ruby packages, which involves running gem build followed by gem install.

     The source field of a package that uses this build system typically references a gem archive, since this is the format that Ruby developers use when releasing their software.  The build system unpacks the gem archive, potentially patches the source, runs the test suite, repackages the gem, and installs it.  Additionally, directories and tarballs may be referenced to allow building unreleased gems from Git or a traditional source release tarball.

     Which Ruby package is used can be specified with the #:ruby parameter.  A list of additional flags to be passed to the gem command can be specified with the #:gem-flags parameter.

 -- Scheme Variable: waf-build-system
     This variable is exported by (guix build-system waf).  It implements a build procedure around the waf script.  The common phases---configure, build, and install---are implemented by passing their names as arguments to the waf script.

     The waf script is executed by the Python interpreter.  Which Python package is used to run the script can be specified with the #:python parameter.

 -- Scheme Variable: haskell-build-system
     This variable is exported by (guix build-system haskell).  It implements the Cabal build procedure used by Haskell packages, which involves running runhaskell Setup.hs configure --prefix=/gnu/store/... and runhaskell Setup.hs build. Instead of installing the package by running runhaskell Setup.hs install, to avoid trying to register libraries in the read-only compiler store directory, the build system uses runhaskell Setup.hs copy, followed by runhaskell Setup.hs register.  In addition, the build system generates the package documentation by running runhaskell Setup.hs haddock, unless #:haddock? #f is passed.  Optional Haddock parameters can be passed with the help of the #:haddock-flags parameter.  If the file Setup.hs is not found, the build system looks for Setup.lhs instead.

     Which Haskell compiler is used can be specified with the #:haskell parameter which defaults to ghc.

 -- Scheme Variable: emacs-build-system
     This variable is exported by (guix build-system emacs).  It implements an installation procedure similar to the packaging system of Emacs itself (see Packages (The GNU Emacs Manual)).

     It first creates the PACKAGE-autoloads.el file, then it byte compiles all Emacs Lisp files.  Differently from the Emacs packaging system, the Info documentation files are moved to the standard documentation directory and the dir file is deleted.  Each package is installed in its own directory under share/emacs/site-lisp/guix.d.

Lastly, for packages that do not need anything as sophisticated, a ``trivial'' build system is provided.  It is trivial in the sense that it provides basically no support: it does not pull any implicit inputs, and does not have a notion of build phases.

 -- Scheme Variable: trivial-build-system
     This variable is exported by (guix build-system trivial).

     This build system requires a #:builder argument.  This argument must be a Scheme expression that builds the package output(s)---as with build-expression->derivation (see build-expression->derivation).

The Store
=========

Conceptually, the store is the place where derivations that have been built successfully are stored---by default, /gnu/store. Sub-directories in the store are referred to as store items or sometimes store paths.  The store has an associated database that contains information such as the store paths referred to by each store path, and the list of valid store items---results of successful builds.  This database resides in LOCALSTATEDIR/guix/db, where LOCALSTATEDIR is the state directory specified via --localstatedir at configure time, usually /var.

The store is always accessed by the daemon on behalf of its clients (see Invoking guix-daemon).  To manipulate the store, clients connect to the daemon over a Unix-domain socket, send requests to it, and read the result---these are remote procedure calls, or RPCs.

     Users must never modify files under /gnu/store directly. This would lead to inconsistencies and break the immutability assumptions of Guix's functional model (see Introduction).

     See guix gc --verify, for information on how to check the integrity of the store and attempt recovery from accidental modifications.

The (guix store) module provides procedures to connect to the daemon, and to perform RPCs.  These are described below.

 -- Scheme Procedure: open-connection [FILE] [#:reserve-space? #t]
     Connect to the daemon over the Unix-domain socket at FILE.  When RESERVE-SPACE? is true, instruct it to reserve a little bit of extra space on the file system so that the garbage collector can still operate should the disk become full.  Return a server object.

     FILE defaults to %DEFAULT-SOCKET-PATH, which is the normal location given the options that were passed to configure.

 -- Scheme Procedure: close-connection SERVER
     Close the connection to SERVER.

 -- Scheme Variable: current-build-output-port
     This variable is bound to a SRFI-39 parameter, which refers to the port where build and error logs sent by the daemon should be written.

Procedures that make RPCs all take a server object as their first argument.

 -- Scheme Procedure: valid-path? SERVER PATH
     Return #t when PATH designates a valid store item and #f otherwise (an invalid item may exist on disk but still be invalid, for instance because it is the result of an aborted or failed build.)

     A &nix-protocol-error condition is raised if PATH is not prefixed by the store directory (/gnu/store).

 -- Scheme Procedure: add-text-to-store SERVER NAME TEXT [REFERENCES]
     Add TEXT under file NAME in the store, and return its store path.  REFERENCES is the list of store paths referred to by the resulting store path.

 -- Scheme Procedure: build-derivations SERVER DERIVATIONS
     Build DERIVATIONS (a list of <derivation> objects or derivation paths), and return when the worker is done building them. Return #t on success.

Note that the (guix monads) module provides a monad as well as monadic versions of the above procedures, with the goal of making it more convenient to work with code that accesses the store (see The Store Monad).

This section is currently incomplete.

Derivations
===========

Low-level build actions and the environment in which they are performed are represented by derivations.  A derivation contains the following pieces of information:

  * The outputs of the derivation---derivations produce at least one file or directory in the store, but may produce more.

  * The inputs of the derivations, which may be other derivations or plain files in the store (patches, build scripts, etc.)

  * The system type targeted by the derivation---e.g., x86_64-linux.

  * The file name of a build script in the store, along with the arguments to be passed.

  * A list of environment variables to be defined.

Derivations allow clients of the daemon to communicate build actions to the store.  They exist in two forms: as an in-memory representation, both on the client- and daemon-side, and as files in the store whose name end in .drv---these files are referred to as derivation paths.  Derivations paths can be passed to the build-derivations procedure to perform the build actions they prescribe (see The Store).

The (guix derivations) module provides a representation of derivations as Scheme objects, along with procedures to create and otherwise manipulate derivations.  The lowest-level primitive to create a derivation is the derivation procedure:

 -- Scheme Procedure: derivation STORE NAME BUILDER
     ARGS [#:outputs '("out")] [#:hash #f] [#:hash-algo #f]
     [#:recursive? #f] [#:inputs '()] [#:env-vars '()]
     [#:system (%current-system)] [#:references-graphs #f]
     [#:allowed-references #f] [#:disallowed-references #f]
     [#:leaked-env-vars #f] [#:local-build? #f]
     [#:substitutable? #t]
     Build a derivation with the given arguments, and return the resulting <derivation> object.

     When HASH and HASH-ALGO are given, a fixed-output derivation is created---i.e., one whose result is known in advance, such as a file download.  If, in addition, RECURSIVE? is true, then that fixed output may be an executable file or a directory and HASH must be the hash of an archive containing this output.

     When REFERENCES-GRAPHS is true, it must be a list of file name/store path pairs.  In that case, the reference graph of each store path is exported in the build environment in the corresponding file, in a simple text format.

     When ALLOWED-REFERENCES is true, it must be a list of store items or outputs that the derivation's output may refer to.  Likewise, DISALLOWED-REFERENCES, if true, must be a list of things the outputs may not refer to.

     When LEAKED-ENV-VARS is true, it must be a list of strings denoting environment variables that are allowed to ``leak'' from the daemon's environment to the build environment.  This is only applicable to fixed-output derivations---i.e., when HASH is true.  The main use is to allow variables such as http_proxy to be passed to derivations that download files.

     When LOCAL-BUILD? is true, declare that the derivation is not a good candidate for offloading and should rather be built locally (see Daemon Offload Setup).  This is the case for small derivations where the costs of data transfers would outweigh the benefits.

     When SUBSTITUTABLE? is false, declare that substitutes of the derivation's output should not be used (see Substitutes).  This is useful, for instance, when building packages that capture details of the host CPU instruction set.

Here's an example with a shell script as its builder, assuming STORE is an open connection to the daemon, and BASH points to a Bash executable in the store:

     (use-modules (guix utils)
                  (guix store)
                  (guix derivations))

     (let ((builder   ; add the Bash script to the store
             (add-text-to-store store "my-builder.sh"
                                "echo hello world > $out\n" '())))
       (derivation store "foo"
                   bash `("-e" ,builder)
                   #:inputs `((,bash) (,builder))
                   #:env-vars '(("HOME" . "/homeless"))))
     => #<derivation /gnu/store/...-foo.drv => /gnu/store/...-foo>

As can be guessed, this primitive is cumbersome to use directly.  A better approach is to write build scripts in Scheme, of course!  The best course of action for that is to write the build code as a ``G-expression'', and to pass it to gexp->derivation.  For more information, see G-Expressions.

Once upon a time, gexp->derivation did not exist and constructing derivations with build code written in Scheme was achieved with build-expression->derivation, documented below.  This procedure is now deprecated in favor of the much nicer gexp->derivation.

 -- Scheme Procedure: build-expression->derivation STORE
     NAME EXP
     [#:system (%current-system)] [#:inputs '()]
     [#:outputs '("out")] [#:hash #f] [#:hash-algo #f]
     [#:recursive? #f] [#:env-vars '()] [#:modules '()]
     [#:references-graphs #f] [#:allowed-references #f]
     [#:disallowed-references #f]
     [#:local-build? #f] [#:substitutable? #t] [#:guile-for-build #f]
     Return a derivation that executes Scheme expression EXP as a builder for derivation NAME.  INPUTS must be a list of (name drv-path sub-drv) tuples; when SUB-DRV is omitted, "out" is assumed.  MODULES is a list of names of Guile modules from the current search path to be copied in the store, compiled, and made available in the load path during the execution of EXP---e.g., ((guix build utils) (guix build gnu-build-system)).

     EXP is evaluated in an environment where %outputs is bound to a list of output/path pairs, and where %build-inputs is bound to a list of string/output-path pairs made from INPUTS. Optionally, ENV-VARS is a list of string pairs specifying the name and value of environment variables visible to the builder.  The builder terminates by passing the result of EXP to exit; thus, when EXP returns #f, the build is considered to have failed.

     EXP is built using GUILE-FOR-BUILD (a derivation).  When GUILE-FOR-BUILD is omitted or is #f, the value of the %guile-for-build fluid is used instead.

     See the derivation procedure for the meaning of REFERENCES-GRAPHS, ALLOWED-REFERENCES, DISALLOWED-REFERENCES, LOCAL-BUILD?, and SUBSTITUTABLE?.

Here's an example of a single-output derivation that creates a directory containing one file:

     (let ((builder '(let ((out (assoc-ref %outputs "out")))
                       (mkdir out)    ; create /gnu/store/...-goo
                       (call-with-output-file (string-append out "/test")
                         (lambda (p)
                           (display '(hello guix) p))))))
       (build-expression->derivation store "goo" builder))

     => #<derivation /gnu/store/...-goo.drv => ...>

The Store Monad
===============

The procedures that operate on the store described in the previous sections all take an open connection to the build daemon as their first argument.  Although the underlying model is functional, they either have side effects or depend on the current state of the store.

The former is inconvenient: the connection to the build daemon has to be carried around in all those functions, making it impossible to compose functions that do not take that parameter with functions that do.  The latter can be problematic: since store operations have side effects and/or depend on external state, they have to be properly sequenced.

This is where the (guix monads) module comes in.  This module provides a framework for working with monads, and a particularly useful monad for our uses, the store monad.  Monads are a construct that allows two things: associating ``context'' with values (in our case, the context is the store), and building sequences of computations (here computations include accesses to the store).  Values in a monad---values that carry this additional context---are called monadic values; procedures that return such values are called monadic procedures.

Consider this ``normal'' procedure:

     (define (sh-symlink store)
       ;; Return a derivation that symlinks the 'bash' executable.
       (let* ((drv (package-derivation store bash))
              (out (derivation->output-path drv))
              (sh  (string-append out "/bin/bash")))
         (build-expression->derivation store "sh"
                                       `(symlink ,sh %output))))

Using (guix monads) and (guix gexp), it may be rewritten as a monadic function:

     (define (sh-symlink)
       ;; Same, but return a monadic value.
       (mlet %store-monad ((drv (package->derivation bash)))
         (gexp->derivation "sh"
                           #~(symlink (string-append #$drv "/bin/bash")
                                      #$output))))

There are several things to note in the second version: the store parameter is now implicit and is ``threaded'' in the calls to the package->derivation and gexp->derivation monadic procedures, and the monadic value returned by package->derivation is bound using mlet instead of plain let.

As it turns out, the call to package->derivation can even be omitted since it will take place implicitly, as we will see later (see G-Expressions):

     (define (sh-symlink)
       (gexp->derivation "sh"
                         #~(symlink (string-append #$bash "/bin/bash")
                                    #$output)))

Calling the monadic sh-symlink has no effect.  As someone once said, ``you exit a monad like you exit a building on fire: by running''. So, to exit the monad and get the desired effect, one must use run-with-store:

     (run-with-store (open-connection) (sh-symlink))
     => /gnu/store/...-sh-symlink

Note that the (guix monad-repl) module extends the Guile REPL with new ``meta-commands'' to make it easier to deal with monadic procedures: run-in-store, and enter-store-monad.  The former is used to ``run'' a single monadic value through the store:

     scheme@(guile-user)> ,run-in-store (package->derivation hello)
     $1 = #<derivation /gnu/store/...-hello-2.9.drv => ...>

The latter enters a recursive REPL, where all the return values are automatically run through the store:

     scheme@(guile-user)> ,enter-store-monad
     store-monad@(guile-user) [1]> (package->derivation hello)
     $2 = #<derivation /gnu/store/...-hello-2.9.drv => ...>
     store-monad@(guile-user) [1]> (text-file "foo" "Hello!")
     $3 = "/gnu/store/...-foo"
     store-monad@(guile-user) [1]> ,q
     scheme@(guile-user)>

Note that non-monadic values cannot be returned in the store-monad REPL.

The main syntactic forms to deal with monads in general are provided by the (guix monads) module and are described below.

 -- Scheme Syntax: with-monad MONAD BODY ...
     Evaluate any >>= or return forms in BODY as being in MONAD.

 -- Scheme Syntax: return VAL
     Return a monadic value that encapsulates VAL.

 -- Scheme Syntax: >>= MVAL MPROC ...
     Bind monadic value MVAL, passing its ``contents'' to monadic procedures MPROC... (This operation is commonly referred to as ``bind'', but that name denotes an unrelated procedure in Guile.  Thus we use this somewhat cryptic symbol inherited from the Haskell language.).  There can be one MPROC or several of them, as in this example:

          (run-with-state
              (with-monad %state-monad
                (>>= (return 1)
                     (lambda (x) (return (+ 1 x)))
                     (lambda (x) (return (* 2 x)))))
            'some-state)

          => 4
          => some-state

 -- Scheme Syntax: mlet MONAD ((VAR MVAL) ...)
     BODY ...
 -- Scheme Syntax: mlet* MONAD ((VAR MVAL) ...)
     BODY ...
     Bind the variables VAR to the monadic values MVAL in BODY.  The form (VAR -> VAL) binds VAR to the ``normal'' value VAL, as per let.

     mlet* is to mlet what let* is to let (see Local Bindings (GNU Guile Reference Manual)).

 -- Scheme System: mbegin MONAD MEXP ...
     Bind MEXP and the following monadic expressions in sequence, returning the result of the last expression.

     This is akin to mlet, except that the return values of the monadic expressions are ignored.  In that sense, it is analogous to begin, but applied to monadic expressions.

The (guix monads) module provides the state monad, which allows an additional value---the state---to be threaded through monadic procedure calls.

 -- Scheme Variable: %state-monad
     The state monad.  Procedures in the state monad can access and change the state that is threaded.

     Consider the example below.  The square procedure returns a value in the state monad.  It returns the square of its argument, but also increments the current state value:

          (define (square x)
            (mlet %state-monad ((count (current-state)))
              (mbegin %state-monad
                (set-current-state (+ 1 count))
                (return (* x x)))))

          (run-with-state (sequence %state-monad (map square (iota 3))) 0)
          => (0 1 4)
          => 3

     When ``run'' through %STATE-MONAD, we obtain that additional state value, which is the number of square calls.

 -- Monadic Procedure: current-state
     Return the current state as a monadic value.

 -- Monadic Procedure: set-current-state VALUE
     Set the current state to VALUE and return the previous state as a monadic value.

 -- Monadic Procedure: state-push VALUE
     Push VALUE to the current state, which is assumed to be a list, and return the previous state as a monadic value.

 -- Monadic Procedure: state-pop
     Pop a value from the current state and return it as a monadic value. The state is assumed to be a list.

 -- Scheme Procedure: run-with-state MVAL [STATE]
     Run monadic value MVAL starting with STATE as the initial state.  Return two values: the resulting value, and the resulting state.

The main interface to the store monad, provided by the (guix store) module, is as follows.

 -- Scheme Variable: %store-monad
     The store monad---an alias for %STATE-MONAD.

     Values in the store monad encapsulate accesses to the store.  When its effect is needed, a value of the store monad must be ``evaluated'' by passing it to the run-with-store procedure (see below.)

 -- Scheme Procedure: run-with-store STORE MVAL [#:guile-for-build] [#:system (%current-system)]
     Run MVAL, a monadic value in the store monad, in STORE, an open store connection.

 -- Monadic Procedure: text-file NAME TEXT [REFERENCES]
     Return as a monadic value the absolute file name in the store of the file containing TEXT, a string.  REFERENCES is a list of store items that the resulting text file refers to; it defaults to the empty list.

 -- Monadic Procedure: interned-file FILE [NAME]
     [#:recursive? #t] [#:select? (const #t)]
     Return the name of FILE once interned in the store.  Use NAME as its store name, or the basename of FILE if NAME is omitted.

     When RECURSIVE? is true, the contents of FILE are added recursively; if FILE designates a flat file and RECURSIVE? is true, its contents are added, and its permission bits are kept.

     When RECURSIVE? is true, call (SELECT? FILE STAT) for each directory entry, where FILE is the entry's absolute file name and STAT is the result of lstat; exclude entries for which SELECT? does not return true.

     The example below adds a file to the store, under two different names:

          (run-with-store (open-connection)
            (mlet %store-monad ((a (interned-file "README"))
                                (b (interned-file "README" "LEGU-MIN")))
              (return (list a b))))

          => ("/gnu/store/rwm...-README" "/gnu/store/44i...-LEGU-MIN")

The (guix packages) module exports the following package-related monadic procedures:

 -- Monadic Procedure: package-file PACKAGE [FILE]
     [#:system (%current-system)] [#:target #f]
     [#:output "out"]
     Return as a monadic value in the absolute file name of FILE within the OUTPUT directory of PACKAGE.  When FILE is omitted, return the name of the OUTPUT directory of PACKAGE.  When TARGET is true, use it as a cross-compilation target triplet.

 -- Monadic Procedure: package->derivation PACKAGE [SYSTEM]
 -- Monadic Procedure: package->cross-derivation PACKAGE
     TARGET [SYSTEM]
     Monadic version of package-derivation and package-cross-derivation (see Defining Packages).

G-Expressions
=============

So we have ``derivations'', which represent a sequence of build actions to be performed to produce an item in the store (see Derivations). These build actions are performed when asking the daemon to actually build the derivations; they are run by the daemon in a container (see Invoking guix-daemon).

It should come as no surprise that we like to write these build actions in Scheme.  When we do that, we end up with two strata of Scheme code (The term stratum in this context was coined by Manuel Serrano et al. in the context of their work on Hop.  Oleg Kiselyov, who has written insightful essays and code on this topic (http://okmij.org/ftp/meta-programming/#meta-scheme), refers to this kind of code generation as staging.): the ``host code''---code that defines packages, talks to the daemon, etc.---and the ``build code''---code that actually performs build actions, such as making directories, invoking make, etc.

To describe a derivation and its build actions, one typically needs to embed build code inside host code.  It boils down to manipulating build code as data, and the homoiconicity of Scheme---code has a direct representation as data---comes in handy for that.  But we need more than the normal quasiquote mechanism in Scheme to construct build expressions.

The (guix gexp) module implements G-expressions, a form of S-expressions adapted to build expressions.  G-expressions, or gexps, consist essentially of three syntactic forms: gexp, ungexp, and ungexp-splicing (or simply: #~, #$, and #$@), which are comparable to quasiquote, unquote, and unquote-splicing, respectively (see quasiquote (GNU Guile Reference Manual)).  However, there are major differences:

  * Gexps are meant to be written to a file and run or manipulated by other processes.

  * When a high-level object such as a package or derivation is unquoted inside a gexp, the result is as if its output file name had been introduced.

  * Gexps carry information about the packages or derivations they refer to, and these dependencies are automatically added as inputs to the build processes that use them.

This mechanism is not limited to package and derivation objects: compilers able to ``lower'' other high-level objects to derivations or files in the store can be defined, such that these objects can also be inserted into gexps.  For example, a useful type of high-level objects that can be inserted in a gexp is ``file-like objects'', which make it easy to add files to the store and to refer to them in derivations and such (see local-file and plain-file below.)

To illustrate the idea, here is an example of a gexp:

     (define build-exp
       #~(begin
           (mkdir #$output)
           (chdir #$output)
           (symlink (string-append #$coreutils "/bin/ls")
                    "list-files")))

This gexp can be passed to gexp->derivation; we obtain a derivation that builds a directory containing exactly one symlink to /gnu/store/...-coreutils-8.22/bin/ls:

     (gexp->derivation "the-thing" build-exp)

As one would expect, the "/gnu/store/...-coreutils-8.22" string is substituted to the reference to the COREUTILS package in the actual build code, and COREUTILS is automatically made an input to the derivation.  Likewise, #$output (equivalent to (ungexp output)) is replaced by a string containing the directory name of the output of the derivation.

In a cross-compilation context, it is useful to distinguish between references to the native build of a package---that can run on the host---versus references to cross builds of a package.  To that end, the #+ plays the same role as #$, but is a reference to a native package build:

     (gexp->derivation "vi"
        #~(begin
            (mkdir #$output)
            (system* (string-append #+coreutils "/bin/ln")
                     "-s"
                     (string-append #$emacs "/bin/emacs")
                     (string-append #$output "/bin/vi")))
        #:target "mips64el-linux-gnu")

In the example above, the native build of COREUTILS is used, so that ln can actually run on the host; but then the cross-compiled build of EMACS is referenced.

Another gexp feature is imported modules: sometimes you want to be able to use certain Guile modules from the ``host environment'' in the gexp, so those modules should be imported in the ``build environment''. The with-imported-modules form allows you to express that:

     (let ((build (with-imported-modules '((guix build utils))
                    #~(begin
                        (use-modules (guix build utils))
                        (mkdir-p (string-append #$output "/bin"))))))
       (gexp->derivation "empty-dir"
                         #~(begin
                             #$build
                             (display "success!\n")
                             #t)))

In this example, the (guix build utils) module is automatically pulled into the isolated build environment of our gexp, such that (use-modules (guix build utils)) works as expected.

Usually you want the closure of the module to be imported---i.e., the module itself and all the modules it depends on---rather than just the module; failing to do that, attempts to use the module will fail because of missing dependent modules.  The source-module-closure procedure computes the closure of a module by looking at its source file headers, which comes in handy in this case:

     (use-modules (guix modules))   ;for 'source-module-closure'

     (with-imported-modules (source-module-closure
                              '((guix build utils)
                                (gnu build vm)))
       (gexp->derivation "something-with-vms"
                         #~(begin
                             (use-modules (guix build utils)
                                          (gnu build vm))
                             ...)))

The syntactic form to construct gexps is summarized below.

 -- Scheme Syntax: #~EXP
 -- Scheme Syntax: (gexp EXP)
     Return a G-expression containing EXP.  EXP may contain one or more of the following forms:

     #$OBJ
     (ungexp OBJ)
          Introduce a reference to OBJ.  OBJ may have one of the supported types, for example a package or a derivation, in which case the ungexp form is replaced by its output file name---e.g., "/gnu/store/...-coreutils-8.22.

          If OBJ is a list, it is traversed and references to supported objects are substituted similarly.

          If OBJ is another gexp, its contents are inserted and its dependencies are added to those of the containing gexp.

          If OBJ is another kind of object, it is inserted as is.

     #$OBJ:OUTPUT
     (ungexp OBJ OUTPUT)
          This is like the form above, but referring explicitly to the OUTPUT of OBJ---this is useful when OBJ produces multiple outputs (see Packages with Multiple Outputs).

     #+OBJ
     #+OBJ:output
     (ungexp-native OBJ)
     (ungexp-native OBJ OUTPUT)
          Same as ungexp, but produces a reference to the native build of OBJ when used in a cross compilation context.

     #$output[:OUTPUT]
     (ungexp output [OUTPUT])
          Insert a reference to derivation output OUTPUT, or to the main output when OUTPUT is omitted.

          This only makes sense for gexps passed to gexp->derivation.

     #$@LST
     (ungexp-splicing LST)
          Like the above, but splices the contents of LST inside the containing list.

     #+@LST
     (ungexp-native-splicing LST)
          Like the above, but refers to native builds of the objects listed in LST.

     G-expressions created by gexp or #~ are run-time objects of the gexp? type (see below.)

 -- Scheme Syntax: with-imported-modules MODULES BODY...
     Mark the gexps defined in BODY... as requiring MODULES in their execution environment.  MODULES must be a list of Guile module names, such as '((guix build utils) (guix build gremlin)).

     This form has lexical scope: it has an effect on the gexps directly defined in BODY..., but not on those defined, say, in procedures called from BODY....

 -- Scheme Procedure: gexp? OBJ
     Return #t if OBJ is a G-expression.

G-expressions are meant to be written to disk, either as code building some derivation, or as plain files in the store.  The monadic procedures below allow you to do that (see The Store Monad, for more information about monads.)

 -- Monadic Procedure: gexp->derivation NAME EXP
     [#:system (%current-system)] [#:target #f] [#:graft? #t]
     [#:hash #f] [#:hash-algo #f]
     [#:recursive? #f] [#:env-vars '()] [#:modules '()]
     [#:module-path %LOAD-PATH]
     [#:references-graphs #f] [#:allowed-references #f]
     [#:disallowed-references #f]
     [#:leaked-env-vars #f]
     [#:script-name (string-append NAME "-builder")]
     [#:local-build? #f] [#:substitutable? #t] [#:guile-for-build #f]
     Return a derivation NAME that runs EXP (a gexp) with GUILE-FOR-BUILD (a derivation) on SYSTEM; EXP is stored in a file called SCRIPT-NAME.  When TARGET is true, it is used as the cross-compilation target triplet for packages referred to by EXP.

     MODULES is deprecated in favor of with-imported-modules. Its meaning is to make MODULES available in the evaluation context of EXP; MODULES is a list of names of Guile modules searched in MODULE-PATH to be copied in the store, compiled, and made available in the load path during the execution of EXP---e.g., ((guix build utils) (guix build gnu-build-system)).

     GRAFT? determines whether packages referred to by EXP should be grafted when applicable.

     When REFERENCES-GRAPHS is true, it must be a list of tuples of one of the following forms:

          (FILE-NAME PACKAGE)
          (FILE-NAME PACKAGE OUTPUT)
          (FILE-NAME DERIVATION)
          (FILE-NAME DERIVATION OUTPUT)
          (FILE-NAME STORE-ITEM)

     The right-hand-side of each element of REFERENCES-GRAPHS is automatically made an input of the build process of EXP.  In the build environment, each FILE-NAME contains the reference graph of the corresponding item, in a simple text format.

     ALLOWED-REFERENCES must be either #f or a list of output names and packages. In the latter case, the list denotes store items that the result is allowed to refer to.  Any reference to another store item will lead to a build error. Similarly for DISALLOWED-REFERENCES, which can list items that must not be referenced by the outputs.

     The other arguments are as for derivation (see Derivations).

The local-file, plain-file, computed-file, program-file, and scheme-file procedures below return file-like objects.  That is, when unquoted in a G-expression, these objects lead to a file in the store.  Consider this G-expression:

     #~(system* #$(file-append glibc "/sbin/nscd") "-f"
                #$(local-file "/tmp/my-nscd.conf"))

The effect here is to ``intern'' /tmp/my-nscd.conf by copying it to the store.  Once expanded, for instance via gexp->derivation, the G-expression refers to that copy under /gnu/store; thus, modifying or removing the file in /tmp does not have any effect on what the G-expression does. plain-file can be used similarly; it differs in that the file content is directly passed as a string.

 -- Scheme Procedure: local-file FILE [NAME]
     [#:recursive? #f] [#:select? (const #t)]
     Return an object representing local file FILE to add to the store; this object can be used in a gexp.  If FILE is a relative file name, it is looked up relative to the source file where this form appears.  FILE will be added to the store under NAME--by default the base name of FILE.

     When RECURSIVE? is true, the contents of FILE are added recursively; if FILE designates a flat file and RECURSIVE? is true, its contents are added, and its permission bits are kept.

     When RECURSIVE? is true, call (SELECT? FILE STAT) for each directory entry, where FILE is the entry's absolute file name and STAT is the result of lstat; exclude entries for which SELECT? does not return true.

     This is the declarative counterpart of the interned-file monadic procedure (see interned-file).

 -- Scheme Procedure: plain-file NAME CONTENT
     Return an object representing a text file called NAME with the given CONTENT (a string) to be added to the store.

     This is the declarative counterpart of text-file.

 -- Scheme Procedure: computed-file NAME GEXP
     [#:options '(#:local-build? #t)]
     Return an object representing the store item NAME, a file or directory computed by GEXP.  OPTIONS is a list of additional arguments to pass to gexp->derivation.

     This is the declarative counterpart of gexp->derivation.

 -- Monadic Procedure: gexp->script NAME EXP
     Return an executable script NAME that runs EXP using GUILE, with EXP's imported modules in its search path.

     The example below builds a script that simply invokes the ls command:

          (use-modules (guix gexp) (gnu packages base))

          (gexp->script "list-files"
                        #~(execl #$(file-append coreutils "/bin/ls")
                                 "ls"))

     When ``running'' it through the store (see run-with-store), we obtain a derivation that produces an executable file /gnu/store/...-list-files along these lines:

          #!/gnu/store/...-guile-2.0.11/bin/guile -ds
          !#
          (execl "/gnu/store/...-coreutils-8.22"/bin/ls" "ls")

 -- Scheme Procedure: program-file NAME EXP
     [#:guile #f]
     Return an object representing the executable store item NAME that runs GEXP.  GUILE is the Guile package used to execute that script.

     This is the declarative counterpart of gexp->script.

 -- Monadic Procedure: gexp->file NAME EXP
     [#:set-load-path? #t]
     Return a derivation that builds a file NAME containing EXP. When SET-LOAD-PATH? is true, emit code in the resulting file to set %load-path and %load-compiled-path to honor EXP's imported modules.

     The resulting file holds references to all the dependencies of EXP or a subset thereof.

 -- Scheme Procedure: scheme-file NAME EXP
     Return an object representing the Scheme file NAME that contains EXP.

     This is the declarative counterpart of gexp->file.

 -- Monadic Procedure: text-file* NAME TEXT ...
     Return as a monadic value a derivation that builds a text file containing all of TEXT.  TEXT may list, in addition to strings, objects of any type that can be used in a gexp: packages, derivations, local file objects, etc.  The resulting store file holds references to all these.

     This variant should be preferred over text-file anytime the file to create will reference items from the store.  This is typically the case when building a configuration file that embeds store file names, like this:

          (define (profile.sh)
            ;; Return the name of a shell script in the store that
            ;; initializes the 'PATH' environment variable.
            (text-file* "profile.sh"
                        "export PATH=" coreutils "/bin:"
                        grep "/bin:" sed "/bin\n"))

     In this example, the resulting /gnu/store/...-profile.sh file will reference COREUTILS, GREP, and SED, thereby preventing them from being garbage-collected during its lifetime.

 -- Scheme Procedure: mixed-text-file NAME TEXT ...
     Return an object representing store file NAME containing TEXT.  TEXT is a sequence of strings and file-like objects, as in:

          (mixed-text-file "profile"
                           "export PATH=" coreutils "/bin:" grep "/bin")

     This is the declarative counterpart of text-file*.

 -- Scheme Procedure: file-append OBJ SUFFIX ...
     Return a file-like object that expands to the concatenation of OBJ and SUFFIX, where OBJ is a lowerable object and each SUFFIX is a string.

     As an example, consider this gexp:

          (gexp->script "run-uname"
                        #~(system* #$(file-append coreutils
                                                  "/bin/uname")))

     The same effect could be achieved with:

          (gexp->script "run-uname"
                        #~(system* (string-append #$coreutils
                                                  "/bin/uname")))

     There is one difference though: in the file-append case, the resulting script contains the absolute file name as a string, whereas in the second case, the resulting script contains a (string-append ...) expression to construct the file name at run time.

Of course, in addition to gexps embedded in ``host'' code, there are also modules containing build tools.  To make it clear that they are meant to be used in the build stratum, these modules are kept in the (guix build ...) name space.

Internally, high-level objects are lowered, using their compiler, to either derivations or store items.  For instance, lowering a package yields a derivation, and lowering a plain-file yields a store item.  This is achieved using the lower-object monadic procedure.

 -- Monadic Procedure: lower-object OBJ [SYSTEM]
     [#:target #f]
     Return as a value in %STORE-MONAD the derivation or store item corresponding to OBJ for SYSTEM, cross-compiling for TARGET if TARGET is true.  OBJ must be an object that has an associated gexp compiler, such as a <package>.

Utilities
*********

This section describes Guix command-line utilities.  Some of them are primarily targeted at developers and users who write new package definitions, while others are more generally useful.  They complement the Scheme programming interface of Guix in a convenient way.

Invoking guix build
===================

The guix build command builds packages or derivations and their dependencies, and prints the resulting store paths.  Note that it does not modify the user's profile---this is the job of the guix package command (see Invoking guix package).  Thus, it is mainly useful for distribution developers.

The general syntax is:

     guix build OPTIONS PACKAGE-OR-DERIVATION...

As an example, the following command builds the latest versions of Emacs and of Guile, displays their build logs, and finally displays the resulting directories:

     guix build emacs guile

Similarly, the following command builds all the available packages:

     guix build --quiet --keep-going \
       `guix package -A | cut -f1,2 --output-delimiter=@`

PACKAGE-OR-DERIVATION may be either the name of a package found in the software distribution such as coreutils or coreutils-8.20, or a derivation such as /gnu/store/...-coreutils-8.19.drv.  In the former case, a package with the corresponding name (and optionally version) is searched for among the GNU distribution modules (see Package Modules).

Alternatively, the --expression option may be used to specify a Scheme expression that evaluates to a package; this is useful when disambiguating among several same-named packages or package variants is needed.

There may be zero or more OPTIONS.  The available options are described in the subsections below.

Common Build Options
--------------------

A number of options that control the build process are common to guix build and other commands that can spawn builds, such as guix package or guix archive.  These are the following:

--load-path=DIRECTORY
-L DIRECTORY
     Add DIRECTORY to the front of the package module search path (see Package Modules).

     This allows users to define their own packages and make them visible to the command-line tools.

--keep-failed
-K
     Keep the build tree of failed builds.  Thus, if a build fails, its build tree is kept under /tmp, in a directory whose name is shown at the end of the build log.  This is useful when debugging build issues.

--keep-going
-k
     Keep going when some of the derivations fail to build; return only once all the builds have either completed or failed.

     The default behavior is to stop as soon as one of the specified derivations has failed.

--dry-run
-n
     Do not build the derivations.

--fallback
     When substituting a pre-built binary fails, fall back to building packages locally.

--substitute-urls=URLS
     Consider URLS the whitespace-separated list of substitute source URLs, overriding the default list of URLs of guix-daemon (see guix-daemon URLs).

     This means that substitutes may be downloaded from URLS, provided they are signed by a key authorized by the system administrator (see Substitutes).

     When URLS is the empty string, substitutes are effectively disabled.

--no-substitutes
     Do not use substitutes for build products.  That is, always build things locally instead of allowing downloads of pre-built binaries (see Substitutes).

--no-grafts
     Do not ``graft'' packages.  In practice, this means that package updates available as grafts are not applied.  See Security Updates, for more information on grafts.

--rounds=N
     Build each derivation N times in a row, and raise an error if consecutive build results are not bit-for-bit identical.

     This is a useful way to detect non-deterministic builds processes. Non-deterministic build processes are a problem because they make it practically impossible for users to verify whether third-party binaries are genuine.  See Invoking guix challenge, for more.

     Note that, currently, the differing build results are not kept around, so you will have to manually investigate in case of an error---e.g., by stashing one of the build results with guix archive --export (see Invoking guix archive), then rebuilding, and finally comparing the two results.

--no-build-hook
     Do not attempt to offload builds via the ``build hook'' of the daemon (see Daemon Offload Setup).  That is, always build things locally instead of offloading builds to remote machines.

--max-silent-time=SECONDS
     When the build or substitution process remains silent for more than SECONDS, terminate it and report a build failure.

--timeout=SECONDS
     Likewise, when the build or substitution process lasts for more than SECONDS, terminate it and report a build failure.

     By default there is no timeout.  This behavior can be restored with --timeout=0.

--verbosity=LEVEL
     Use the given verbosity level.  LEVEL must be an integer between 0 and 5; higher means more verbose output.  Setting a level of 4 or more may be helpful when debugging setup issues with the build daemon.

--cores=N
-c N
     Allow the use of up to N CPU cores for the build.  The special value 0 means to use as many CPU cores as available.

--max-jobs=N
-M N
     Allow at most N build jobs in parallel.  See --max-jobs, for details about this option and the equivalent guix-daemon option.

Behind the scenes, guix build is essentially an interface to the package-derivation procedure of the (guix packages) module, and to the build-derivations procedure of the (guix derivations) module.

In addition to options explicitly passed on the command line, guix build and other guix commands that support building honor the GUIX_BUILD_OPTIONS environment variable.

 -- Environment Variable: GUIX_BUILD_OPTIONS
     Users can define this variable to a list of command line options that will automatically be used by guix build and other guix commands that can perform builds, as in the example below:

          $ export GUIX_BUILD_OPTIONS="--no-substitutes -c 2 -L /foo/bar"

     These options are parsed independently, and the result is appended to the parsed command-line options.

Package Transformation Options
------------------------------

Another set of command-line options supported by guix build and also guix package are package transformation options.  These are options that make it possible to define package variants---for instance, packages built from different source code. This is a convenient way to create customized packages on the fly without having to type in the definitions of package variants (see Defining Packages).

--with-source=SOURCE
     Use SOURCE as the source of the corresponding package. SOURCE must be a file name or a URL, as for guix download (see Invoking guix download).

     The ``corresponding package'' is taken to be the one specified on the command line the name of which matches the base of SOURCE---e.g., if SOURCE is /src/guile-2.0.10.tar.gz, the corresponding package is guile.  Likewise, the version string is inferred from SOURCE; in the previous example, it is 2.0.10.

     This option allows users to try out versions of packages other than the one provided by the distribution.  The example below downloads ed-1.7.tar.gz from a GNU mirror and uses that as the source for the ed package:

          guix build ed --with-source=mirror://gnu/ed/ed-1.7.tar.gz

     As a developer, --with-source makes it easy to test release candidates:

          guix build guile --with-source=../guile-2.0.9.219-e1bb7.tar.xz

     ... or to build from a checkout in a pristine environment:

          $ git clone git://git.sv.gnu.org/guix.git
          $ guix build guix --with-source=./guix

--with-input=PACKAGE=REPLACEMENT
     Replace dependency on PACKAGE by a dependency on REPLACEMENT.  PACKAGE must be a package name, and REPLACEMENT must be a package specification such as guile or guile@1.8.

     For instance, the following command builds Guix, but replaces its dependency on the current stable version of Guile with a dependency on the development version of Guile, guile-next:

          guix build --with-input=guile=guile-next guix

     This is a recursive, deep replacement.  So in this example, both guix and its dependency guile-json (which also depends on guile) get rebuilt against guile-next.

     This is implemented using the package-input-rewriting Scheme procedure (see package-input-rewriting).

--with-graft=PACKAGE=REPLACEMENT
     This is similar to --with-input but with an important difference: instead of rebuilding all the dependency chain, REPLACEMENT is built and then grafted onto the binaries that were initially referring to PACKAGE.  See Security Updates, for more information on grafts.

     For example, the command below grafts version 3.5.4 of GnuTLS onto Wget and all its dependencies, replacing references to the version of GnuTLS they currently refer to:

          guix build --with-graft=gnutls=gnutls@3.5.4 wget

     This has the advantage of being much faster than rebuilding everything. But there is a caveat: it works if and only if PACKAGE and REPLACEMENT are strictly compatible---for example, if they provide a library, the application binary interface (ABI) of those libraries must be compatible.  If REPLACEMENT is somehow incompatible with PACKAGE, then the resulting package may be unusable.  Use with care!

Additional Build Options
------------------------

The command-line options presented below are specific to guix build.

--quiet
-q
     Build quietly, without displaying the build log.  Upon completion, the build log is kept in /var (or similar) and can always be retrieved using the --log-file option.

--file=FILE
-f FILE

     Build the package or derivation that the code within FILE evaluates to.

     As an example, FILE might contain a package definition like this (see Defining Packages):

               [file package-hello.scm not included]

--expression=EXPR
-e EXPR
     Build the package or derivation EXPR evaluates to.

     For example, EXPR may be (@ (gnu packages guile) guile-1.8), which unambiguously designates this specific variant of version 1.8 of Guile.

     Alternatively, EXPR may be a G-expression, in which case it is used as a build program passed to gexp->derivation (see G-Expressions).

     Lastly, EXPR may refer to a zero-argument monadic procedure (see The Store Monad).  The procedure must return a derivation as a monadic value, which is then passed through run-with-store.

--source
-S
     Build the source derivations of the packages, rather than the packages themselves.

     For instance, guix build -S gcc returns something like /gnu/store/...-gcc-4.7.2.tar.bz2, which is the GCC source tarball.

     The returned source tarball is the result of applying any patches and code snippets specified in the package origin (see Defining Packages).

--sources
     Fetch and return the source of PACKAGE-OR-DERIVATION and all their dependencies, recursively.  This is a handy way to obtain a local copy of all the source code needed to build PACKAGES, allowing you to eventually build them even without network access.  It is an extension of the --source option and can accept one of the following optional argument values:

     package
          This value causes the --sources option to behave in the same way as the --source option.

     all
          Build the source derivations of all packages, including any source that might be listed as inputs.  This is the default value.

               $ guix build --sources tzdata
               The following derivations will be built:
                  /gnu/store/...-tzdata2015b.tar.gz.drv
                  /gnu/store/...-tzcode2015b.tar.gz.drv

     transitive
          Build the source derivations of all packages, as well of all transitive inputs to the packages.  This can be used e.g. to prefetch package source for later offline building.

               $ guix build --sources=transitive tzdata
               The following derivations will be built:
                  /gnu/store/...-tzcode2015b.tar.gz.drv
                  /gnu/store/...-findutils-4.4.2.tar.xz.drv
                  /gnu/store/...-grep-2.21.tar.xz.drv
                  /gnu/store/...-coreutils-8.23.tar.xz.drv
                  /gnu/store/...-make-4.1.tar.xz.drv
                  /gnu/store/...-bash-4.3.tar.xz.drv
               ...

--system=SYSTEM
-s SYSTEM
     Attempt to build for SYSTEM---e.g., i686-linux---instead of the system type of the build host.

     An example use of this is on Linux-based systems, which can emulate different personalities.  For instance, passing --system=i686-linux on an x86_64-linux system allows users to build packages in a complete 32-bit environment.

--target=TRIPLET
     Cross-build for TRIPLET, which must be a valid GNU triplet, such as "mips64el-linux-gnu" (see GNU configuration triplets (GNU Configure and Build System)).

--check
     Rebuild PACKAGE-OR-DERIVATION, which are already available in the store, and raise an error if the build results are not bit-for-bit identical.

     This mechanism allows you to check whether previously installed substitutes are genuine (see Substitutes), or whether the build result of a package is deterministic.  See Invoking guix challenge, for more background information and tools.

     When used in conjunction with --keep-failed, the differing output is kept in the store, under /gnu/store/...-check. This makes it easy to look for differences between the two results.

--derivations
-d
     Return the derivation paths, not the output paths, of the given packages.

--root=FILE
-r FILE
     Make FILE a symlink to the result, and register it as a garbage collector root.

--log-file
     Return the build log file names or URLs for the given PACKAGE-OR-DERIVATION, or raise an error if build logs are missing.

     This works regardless of how packages or derivations are specified.  For instance, the following invocations are equivalent:

          guix build --log-file `guix build -d guile`
          guix build --log-file `guix build guile`
          guix build --log-file guile
          guix build --log-file -e '(@ (gnu packages guile) guile-2.0)'

     If a log is unavailable locally, and unless --no-substitutes is passed, the command looks for a corresponding log on one of the substitute servers (as specified with --substitute-urls.)

     So for instance, imagine you want to see the build log of GDB on MIPS, but you are actually on an x86_64 machine:

          $ guix build --log-file gdb -s mips64el-linux
          https://hydra.gnu.org/log/...-gdb-7.10

     You can freely access a huge library of build logs!

Invoking guix edit
==================

So many packages, so many source files!  The guix edit command facilitates the life of users and packagers by pointing their editor at the source file containing the definition of the specified packages. For instance:

     guix edit gcc@4.9 vim

launches the program specified in the VISUAL or in the EDITOR environment variable to view the recipe of GCC 4.9.3 and that of Vim.

If you are using a Guix Git checkout (see Building from Git), or have created your own packages on GUIX_PACKAGE_PATH (see Defining Packages), you will be able to edit the package recipes. Otherwise, you will be able to examine the read-only recipes for packages currently in the store.

If you are using Emacs, note that the Emacs user interface provides the M-x guix-edit command and a similar functionality in the ``package info'' and ``package list'' buffers created by the M-x guix-search-by-name and similar commands (see Emacs Commands).

Invoking guix download
======================

When writing a package definition, developers typically need to download a source tarball, compute its SHA256 hash, and write that hash in the package definition (see Defining Packages).  The guix download tool helps with this task: it downloads a file from the given URI, adds it to the store, and prints both its file name in the store and its SHA256 hash.

The fact that the downloaded file is added to the store saves bandwidth: when the developer eventually tries to build the newly defined package with guix build, the source tarball will not have to be downloaded again because it is already in the store.  It is also a convenient way to temporarily stash files, which may be deleted eventually (see Invoking guix gc).

The guix download command supports the same URIs as used in package definitions.  In particular, it supports mirror:// URIs. https URIs (HTTP over TLS) are supported provided the Guile bindings for GnuTLS are available in the user's environment; when they are not available, an error is raised.  See how to install the GnuTLS bindings for Guile (GnuTLS-Guile), for more information.

guix download verifies HTTPS server certificates by loading the certificates of X.509 authorities from the directory pointed to by the SSL_CERT_DIR environment variable (see X.509 Certificates), unless --no-check-certificate is used.

The following options are available:

--format=FMT
-f FMT
     Write the hash in the format specified by FMT.  For more information on the valid values for FMT, see Invoking guix hash.

--no-check-certificate
     Do not validate the X.509 certificates of HTTPS servers.

     When using this option, you have absolutely no guarantee that you are communicating with the authentic server responsible for the given URL, which makes you vulnerable to ``man-in-the-middle'' attacks.

--output=FILE
-o FILE
     Save the downloaded file to FILE instead of adding it to the store.

Invoking guix hash
==================

The guix hash command computes the SHA256 hash of a file. It is primarily a convenience tool for anyone contributing to the distribution: it computes the cryptographic hash of a file, which can be used in the definition of a package (see Defining Packages).

The general syntax is:

     guix hash OPTION FILE

When FILE is - (a hyphen), guix hash computes the hash of data read from standard input.  guix hash has the following options:

--format=FMT
-f FMT
     Write the hash in the format specified by FMT.

     Supported formats: nix-base32, base32, base16 (hex and hexadecimal can be used as well).

     If the --format option is not specified, guix hash will output the hash in nix-base32.  This representation is used in the definitions of packages.

--recursive
-r
     Compute the hash on FILE recursively.

     In this case, the hash is computed on an archive containing FILE, including its children if it is a directory.  Some of the metadata of FILE is part of the archive; for instance, when FILE is a regular file, the hash is different depending on whether FILE is executable or not.  Metadata such as time stamps has no impact on the hash (see Invoking guix archive).

--exclude-vcs
-x
     When combined with --recursive, exclude version control system directories (.bzr, .git, .hg, etc.)

     As an example, here is how you would compute the hash of a Git checkout, which is useful when using the git-fetch method (see origin Reference):

          $ git clone http://example.org/foo.git
          $ cd foo
          $ guix hash -rx .

Invoking guix import
====================

The guix import command is useful for people who would like to add a package to the distribution with as little work as possible---a legitimate demand.  The command knows of a few repositories from which it can ``import'' package metadata.  The result is a package definition, or a template thereof, in the format we know (see Defining Packages).

The general syntax is:

     guix import IMPORTER OPTIONS...

IMPORTER specifies the source from which to import package metadata, and OPTIONS specifies a package identifier and other options specific to IMPORTER.  Currently, the available ``importers'' are:

gnu
     Import metadata for the given GNU package.  This provides a template for the latest version of that GNU package, including the hash of its source tarball, and its canonical synopsis and description.

     Additional information such as the package dependencies and its license needs to be figured out manually.

     For example, the following command returns a package definition for GNU Hello:

          guix import gnu hello

     Specific command-line options are:

     --key-download=POLICY
          As for guix refresh, specify the policy to handle missing OpenPGP keys when verifying the package signature.  See --key-download.

pypi
     Import metadata from the Python Package Index (https://pypi.python.org/) (This functionality requires Guile-JSON to be installed. See Requirements.).  Information is taken from the JSON-formatted description available at pypi.python.org and usually includes all the relevant information, including package dependencies.  For maximum efficiency, it is recommended to install the unzip utility, so that the importer can unzip Python wheels and gather data from them.

     The command below imports metadata for the itsdangerous Python package:

          guix import pypi itsdangerous

gem
     Import metadata from RubyGems (https://rubygems.org/) (This functionality requires Guile-JSON to be installed.  See Requirements.).  Information is taken from the JSON-formatted description available at rubygems.org and includes most relevant information, including runtime dependencies.  There are some caveats, however.  The metadata doesn't distinguish between synopses and descriptions, so the same string is used for both fields. Additionally, the details of non-Ruby dependencies required to build native extensions is unavailable and left as an exercise to the packager.

     The command below imports metadata for the rails Ruby package:

          guix import gem rails

cpan
     Import metadata from MetaCPAN (https://www.metacpan.org/) (This functionality requires Guile-JSON to be installed. See Requirements.). Information is taken from the JSON-formatted metadata provided through MetaCPAN's API (https://api.metacpan.org/) and includes most relevant information, such as module dependencies.  License information should be checked closely.  If Perl is available in the store, then the corelist utility will be used to filter core modules out of the list of dependencies.

     The command command below imports metadata for the Acme::Boolean Perl module:

          guix import cpan Acme::Boolean

cran
     Import metadata from CRAN (http://cran.r-project.org/), the central repository for the GNU R statistical and graphical environment (http://r-project.org).

     Information is extracted from the DESCRIPTION file of the package.

     The command command below imports metadata for the Cairo R package:

          guix import cran Cairo

     When --recursive is added, the importer will traverse the dependency graph of the given upstream package recursively and generate package expressions for all those packages that are not yet in Guix.

     When --archive=bioconductor is added, metadata is imported from Bioconductor (http://www.bioconductor.org/), a repository of R packages for for the analysis and comprehension of high-throughput genomic data in bioinformatics.

     Information is extracted from the DESCRIPTION file of a package published on the web interface of the Bioconductor SVN repository.

     The command below imports metadata for the GenomicRanges R package:

          guix import cran --archive=bioconductor GenomicRanges

nix
     Import metadata from a local copy of the source of the Nixpkgs distribution (http://nixos.org/nixpkgs/) (This relies on the nix-instantiate command of Nix (http://nixos.org/nix/).).  Package definitions in Nixpkgs are typically written in a mixture of Nix-language and Bash code.  This command only imports the high-level package structure that is written in the Nix language.  It normally includes all the basic fields of a package definition.

     When importing a GNU package, the synopsis and descriptions are replaced by their canonical upstream variant.

     Usually, you will first need to do:

          export NIX_REMOTE=daemon

     so that nix-instantiate does not try to open the Nix database.

     As an example, the command below imports the package definition of LibreOffice (more precisely, it imports the definition of the package bound to the libreoffice top-level attribute):

          guix import nix ~/path/to/nixpkgs libreoffice

hackage
     Import metadata from the Haskell community's central package archive Hackage (https://hackage.haskell.org/).  Information is taken from Cabal files and includes all the relevant information, including package dependencies.

     Specific command-line options are:

     --stdin
     -s
          Read a Cabal file from standard input.

     --no-test-dependencies
     -t
          Do not include dependencies required only by the test suites.

     --cabal-environment=ALIST
     -e ALIST
          ALIST is a Scheme alist defining the environment in which the Cabal conditionals are evaluated.  The accepted keys are: os, arch, impl and a string representing the name of a flag. The value associated with a flag has to be either the symbol true or false.  The value associated with other keys has to conform to the Cabal file format definition.  The default value associated with the keys os, arch and impl is linux, x86_64 and ghc, respectively.

     The command below imports metadata for the latest version of the HTTP Haskell package without including test dependencies and specifying the value of the flag network-uri as false:

          guix import hackage -t -e "'((\"network-uri\" . false))" HTTP

     A specific package version may optionally be specified by following the package name by an at-sign and a version number as in the following example:

          guix import hackage mtl@2.1.3.1

elpa
     Import metadata from an Emacs Lisp Package Archive (ELPA) package repository (see Packages (The GNU Emacs Manual)).

     Specific command-line options are:

     --archive=REPO
     -a REPO
          REPO identifies the archive repository from which to retrieve the information.  Currently the supported repositories and their identifiers are:

            - GNU (http://elpa.gnu.org/packages), selected by the gnu identifier.  This is the default.

               Packages from elpa.gnu.org are signed with one of the keys contained in the GnuPG keyring at share/emacs/25.1/etc/package-keyring.gpg (or similar) in the emacs package (see ELPA package signatures (The GNU Emacs Manual)).

            - MELPA-Stable (http://stable.melpa.org/packages), selected by the melpa-stable identifier.

            - MELPA (http://melpa.org/packages), selected by the melpa identifier.

crate
     Import metadata from the crates.io Rust package repository crates.io (https://crates.io).

The structure of the guix import code is modular.  It would be useful to have more importers for other package formats, and your help is welcome here (see Contributing).

Invoking guix refresh
=====================

The primary audience of the guix refresh command is developers of the GNU software distribution.  By default, it reports any packages provided by the distribution that are outdated compared to the latest upstream version, like this:

     $ guix refresh
     gnu/packages/gettext.scm:29:13: gettext would be upgraded from 0.18.1.1 to 0.18.2.1
     gnu/packages/glib.scm:77:12: glib would be upgraded from 2.34.3 to 2.37.0

Alternately, one can specify packages to consider, in which case a warning is emitted for packages that lack an updater:

     $ guix refresh coreutils guile guile-ssh
     gnu/packages/ssh.scm:205:2: warning: no updater for guile-ssh
     gnu/packages/guile.scm:136:12: guile would be upgraded from 2.0.12 to 2.0.13

guix refresh browses the upstream repository of each package and determines the highest version number of the releases therein.  The command knows how to update specific types of packages: GNU packages, ELPA packages, etc.---see the documentation for --type below.  There are many packages, though, for which it lacks a method to determine whether a new upstream release is available.  However, the mechanism is extensible, so feel free to get in touch with us to add a new method!

When passed --update, it modifies distribution source files to update the version numbers and source tarball hashes of those package recipes (see Defining Packages).  This is achieved by downloading each package's latest source tarball and its associated OpenPGP signature, authenticating the downloaded tarball against its signature using gpg, and finally computing its hash.  When the public key used to sign the tarball is missing from the user's keyring, an attempt is made to automatically retrieve it from a public key server; when this is successful, the key is added to the user's keyring; otherwise, guix refresh reports an error.

The following options are supported:

--expression=EXPR
-e EXPR
     Consider the package EXPR evaluates to.

     This is useful to precisely refer to a package, as in this example:

          guix refresh -l -e '(@@ (gnu packages commencement) glibc-final)'

     This command lists the dependents of the ``final'' libc (essentially all the packages.)

--update
-u
     Update distribution source files (package recipes) in place.  This is usually run from a checkout of the Guix source tree (see Running Guix Before It Is Installed):

          $ ./pre-inst-env guix refresh -s non-core -u

     See Defining Packages, for more information on package definitions.

--select=[SUBSET]
-s SUBSET
     Select all the packages in SUBSET, one of core or non-core.

     The core subset refers to all the packages at the core of the distribution---i.e., packages that are used to build ``everything else''.  This includes GCC, libc, Binutils, Bash, etc.  Usually, changing one of these packages in the distribution entails a rebuild of all the others.  Thus, such updates are an inconvenience to users in terms of build time or bandwidth used to achieve the upgrade.

     The non-core subset refers to the remaining packages.  It is typically useful in cases where an update of the core packages would be inconvenient.

--type=UPDATER
-t UPDATER
     Select only packages handled by UPDATER (may be a comma-separated list of updaters).  Currently, UPDATER may be one of:

     gnu
          the updater for GNU packages;

     gnome
          the updater for GNOME packages;

     kde
          the updater for KDE packages;

     xorg
          the updater for X.org packages;

     kernel.org
          the updater for packages hosted on kernel.org;

     elpa
          the updater for ELPA (http://elpa.gnu.org/) packages;

     cran
          the updater for CRAN (http://cran.r-project.org/) packages;

     bioconductor
          the updater for Bioconductor (http://www.bioconductor.org/) R packages;

     cpan
          the updater for CPAN (http://www.cpan.org/) packages;

     pypi
          the updater for PyPI (https://pypi.python.org) packages.

     gem
          the updater for RubyGems (https://rubygems.org) packages.

     github
          the updater for GitHub (https://github.com) packages.

     hackage
          the updater for Hackage (https://hackage.haskell.org) packages.

     crate
          the updater for Crates (https://crates.io) packages.

     For instance, the following command only checks for updates of Emacs packages hosted at elpa.gnu.org and for updates of CRAN packages:

          $ guix refresh --type=elpa,cran
          gnu/packages/statistics.scm:819:13: r-testthat would be upgraded from 0.10.0 to 0.11.0
          gnu/packages/emacs.scm:856:13: emacs-auctex would be upgraded from 11.88.6 to 11.88.9

In addition, guix refresh can be passed one or more package names, as in this example:

     $ ./pre-inst-env guix refresh -u emacs idutils gcc@4.8

The command above specifically updates the emacs and idutils packages.  The --select option would have no effect in this case.

When considering whether to upgrade a package, it is sometimes convenient to know which packages would be affected by the upgrade and should be checked for compatibility.  For this the following option may be used when passing guix refresh one or more package names:

--list-updaters
-L
     List available updaters and exit (see --type above.)

     For each updater, display the fraction of packages it covers; at the end, display the fraction of packages covered by all these updaters.

--list-dependent
-l
     List top-level dependent packages that would need to be rebuilt as a result of upgrading one or more packages.

Be aware that the --list-dependent option only approximates the rebuilds that would be required as a result of an upgrade.  More rebuilds might be required under some circumstances.

     $ guix refresh --list-dependent flex
     Building the following 120 packages would ensure 213 dependent packages are rebuilt:
     hop-2.4.0 geiser-0.4 notmuch-0.18 mu-0.9.9.5 cflow-1.4 idutils-4.6 ...

The command above lists a set of packages that could be built to check for compatibility with an upgraded flex package.

The following options can be used to customize GnuPG operation:

--gpg=COMMAND
     Use COMMAND as the GnuPG 2.x command.  COMMAND is searched for in $PATH.

--key-download=POLICY
     Handle missing OpenPGP keys according to POLICY, which may be one of:

     always
          Always download missing OpenPGP keys from the key server, and add them to the user's GnuPG keyring.

     never
          Never try to download missing OpenPGP keys.  Instead just bail out.

     interactive
          When a package signed with an unknown OpenPGP key is encountered, ask the user whether to download it or not.  This is the default behavior.

--key-server=HOST
     Use HOST as the OpenPGP key server when importing a public key.

The github updater uses the GitHub API (https://developer.github.com/v3/) to query for new releases.  When used repeatedly e.g. when refreshing all packages, GitHub will eventually refuse to answer any further API requests.  By default 60 API requests per hour are allowed, and a full refresh on all GitHub packages in Guix requires more than this.  Authentication with GitHub through the use of an API token alleviates these limits.  To use an API token, set the environment variable GUIX_GITHUB_TOKEN to a token procured from https://github.com/settings/tokens or otherwise.

Invoking guix lint
==================

The guix lint command is meant to help package developers avoid common errors and use a consistent style.  It runs a number of checks on a given set of packages in order to find common mistakes in their definitions.  Available checkers include (see --list-checkers for a complete list):

synopsis
description
     Validate certain typographical and stylistic rules about package descriptions and synopses.

inputs-should-be-native
     Identify inputs that should most likely be native inputs.

source
home-page
mirror-url
source-file-name
     Probe home-page and source URLs and report those that are invalid.  Suggest a mirror:// URL when applicable.  Check that the source file name is meaningful, e.g. is not just a version number or ``git-checkout'', without a declared file-name (see origin Reference).

cve
     Report known vulnerabilities found in the Common Vulnerabilities and Exposures (CVE) databases of the current and past year published by the US NIST (https://nvd.nist.gov/download.cfm#CVE_FEED).

     To view information about a particular vulnerability, visit pages such as:

       * https://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-YYYY-ABCD

       * https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-YYYY-ABCD

     where CVE-YYYY-ABCD is the CVE identifier---e.g., CVE-2015-7554.

     Package developers can specify in package recipes the Common Platform Enumeration (CPE) (https://nvd.nist.gov/cpe.cfm) name and version of the package when they differ from the name that Guix uses, as in this example:

          (package
            (name "grub")
            ;; ...
            ;; CPE calls this package "grub2".
            (properties '((cpe-name . "grub2"))))

formatting
     Warn about obvious source code formatting issues: trailing white space, use of tabulations, etc.

The general syntax is:

     guix lint OPTIONS PACKAGE...

If no package is given on the command line, then all packages are checked. The OPTIONS may be zero or more of the following:

--list-checkers
-l
     List and describe all the available checkers that will be run on packages and exit.

--checkers
-c
     Only enable the checkers specified in a comma-separated list using the names returned by --list-checkers.

Invoking guix size
==================

The guix size command helps package developers profile the disk usage of packages.  It is easy to overlook the impact of an additional dependency added to a package, or the impact of using a single output for a package that could easily be split (see Packages with Multiple Outputs).  Such are the typical issues that guix size can highlight.

The command can be passed a package specification such as gcc-4.8 or guile:debug, or a file name in the store.  Consider this example:

     $ guix size coreutils
     store item                               total    self
     /gnu/store/...-coreutils-8.23          70.0    13.9  19.8%
     /gnu/store/...-gmp-6.0.0a              55.3     2.5   3.6%
     /gnu/store/...-acl-2.2.52              53.7     0.5   0.7%
     /gnu/store/...-attr-2.4.46             53.2     0.3   0.5%
     /gnu/store/...-gcc-4.8.4-lib           52.9    15.7  22.4%
     /gnu/store/...-glibc-2.21              37.2    37.2  53.1%

The store items listed here constitute the transitive closure of Coreutils---i.e., Coreutils and all its dependencies, recursively---as would be returned by:

     $ guix gc -R /gnu/store/...-coreutils-8.23

Here the output shows three columns next to store items.  The first column, labeled ``total'', shows the size in mebibytes (MiB) of the closure of the store item---that is, its own size plus the size of all its dependencies.  The next column, labeled ``self'', shows the size of the item itself.  The last column shows the ratio of the size of the item itself to the space occupied by all the items listed here.

In this example, we see that the closure of Coreutils weighs in at 70 MiB, half of which is taken by libc.  (That libc represents a large fraction of the closure is not a problem per se because it is always available on the system anyway.)

When the package passed to guix size is available in the store, guix size queries the daemon to determine its dependencies, and measures its size in the store, similar to du -ms --apparent-size (see du invocation (GNU Coreutils)).

When the given package is not in the store, guix size reports information based on the available substitutes (see Substitutes).  This makes it possible it to profile disk usage of store items that are not even on disk, only available remotely.

You can also specify several package names:

     $ guix size coreutils grep sed bash
     store item                               total    self
     /gnu/store/...-coreutils-8.24          77.8    13.8  13.4%
     /gnu/store/...-grep-2.22               73.1     0.8   0.8%
     /gnu/store/...-bash-4.3.42             72.3     4.7   4.6%
     /gnu/store/...-readline-6.3            67.6     1.2   1.2%
     ...
     total: 102.3 MiB

In this example we see that the combination of the four packages takes 102.3 MiB in total, which is much less than the sum of each closure since they have a lot of dependencies in common.

The available options are:

--substitute-urls=URLS
     Use substitute information from URLS. See the same option for guix build.

--map-file=FILE
     Write a graphical map of disk usage in PNG format to FILE.

     For the example above, the map looks like this:

     map of Coreutils disk usage produced by guix size

     This option requires that Guile-Charting (http://wingolog.org/software/guile-charting/) be installed and visible in Guile's module search path.  When that is not the case, guix size fails as it tries to load it.

--system=SYSTEM
-s SYSTEM
     Consider packages for SYSTEM---e.g., x86_64-linux.

Invoking guix graph
===================

Packages and their dependencies form a graph, specifically a directed acyclic graph (DAG).  It can quickly become difficult to have a mental model of the package DAG, so the guix graph command provides a visual representation of the DAG.  By default, guix graph emits a DAG representation in the input format of Graphviz (http://www.graphviz.org/), so its output can be passed directly to the dot command of Graphviz.  It can also emit an HTML page with embedded JavaScript code to display a ``chord diagram'' in a Web browser, using the d3.js (https://d3js.org/) library. The general syntax is:

     guix graph OPTIONS PACKAGE...

For example, the following command generates a PDF file representing the package DAG for the GNU Core Utilities, showing its build-time dependencies:

     guix graph coreutils | dot -Tpdf > dag.pdf

The output looks like this:

Dependency graph of the GNU Coreutils

Nice little graph, no?

But there is more than one graph!  The one above is concise: it is the graph of package objects, omitting implicit inputs such as GCC, libc, grep, etc.  It is often useful to have such a concise graph, but sometimes one may want to see more details.  guix graph supports several types of graphs, allowing you to choose the level of detail:

package
     This is the default type used in the example above.  It shows the DAG of package objects, excluding implicit dependencies.  It is concise, but filters out many details.

bag-emerged
     This is the package DAG, including implicit inputs.

     For instance, the following command:

          guix graph --type=bag-emerged coreutils | dot -Tpdf > dag.pdf

     ... yields this bigger graph:

     Detailed dependency graph of the GNU Coreutils

     At the bottom of the graph, we see all the implicit inputs of GNU-BUILD-SYSTEM (see gnu-build-system).

     Now, note that the dependencies of these implicit inputs---that is, the bootstrap dependencies (see Bootstrapping)---are not shown here, for conciseness.

bag
     Similar to bag-emerged, but this time including all the bootstrap dependencies.

bag-with-origins
     Similar to bag, but also showing origins and their dependencies.

derivations
     This is the most detailed representation: It shows the DAG of derivations (see Derivations) and plain store items.  Compared to the above representation, many additional nodes are visible, including build scripts, patches, Guile modules, etc.

     For this type of graph, it is also possible to pass a .drv file name instead of a package name, as in:

          guix graph -t derivation `guix system build -d my-config.scm`

All the types above correspond to build-time dependencies.  The following graph type represents the run-time dependencies:

references
     This is the graph of references of a package output, as returned by guix gc --references (see Invoking guix gc).

     If the given package output is not available in the store, guix graph attempts to obtain dependency information from substitutes.

     Here you can also pass a store file name instead of a package name.  For example, the command below produces the reference graph of your profile (which can be big!):

          guix graph -t references `readlink -f ~/.guix-profile`

referrers
     This is the graph of the referrers of a store item, as returned by guix gc --referrers (see Invoking guix gc).

     This relies exclusively on local information from your store.  For instance, let us suppose that the current Inkscape is available in 10 profiles on your machine; guix graph -t referrers inkscape will show a graph rooted at Inkscape and with those 10 profiles linked to it.

     It can help determine what is preventing a store item from being garbage collected.

The available options are the following:

--type=TYPE
-t TYPE
     Produce a graph output of TYPE, where TYPE must be one of the values listed above.

--list-types
     List the supported graph types.

--backend=BACKEND
-b BACKEND
     Produce a graph using the selected BACKEND.

--list-backends
     List the supported graph backends.

     Currently, the available backends are Graphviz and d3.js.

--expression=EXPR
-e EXPR
     Consider the package EXPR evaluates to.

     This is useful to precisely refer to a package, as in this example:

          guix graph -e '(@@ (gnu packages commencement) gnu-make-final)'

Invoking guix environment
=========================

The purpose of guix environment is to assist hackers in creating reproducible development environments without polluting their package profile.  The guix environment tool takes one or more packages, builds all of their inputs, and creates a shell environment to use them.

The general syntax is:

     guix environment OPTIONS PACKAGE...

The following example spawns a new shell set up for the development of GNU Guile:

     guix environment guile

If the needed dependencies are not built yet, guix environment automatically builds them.  The environment of the new shell is an augmented version of the environment that guix environment was run in. It contains the necessary search paths for building the given package added to the existing environment variables.  To create a ``pure'' environment, in which the original environment variables have been unset, use the --pure option (Users sometimes wrongfully augment environment variables such as PATH in their ~/.bashrc file.  As a consequence, when guix environment launches it, Bash may read ~/.bashrc, thereby introducing ``impurities'' in these environment variables.  It is an error to define such environment variables in .bashrc; instead, they should be defined in .bash_profile, which is sourced only by log-in shells. See Bash Startup Files (The GNU Bash Reference Manual), for details on Bash start-up files.).

guix environment defines the GUIX_ENVIRONMENT variable in the shell it spawns; its value is the file name of the profile of this environment.  This allows users to, say, define a specific prompt for development environments in their .bashrc (see Bash Startup Files (The GNU Bash Reference Manual)):

     if [ -n "$GUIX_ENVIRONMENT" ]
     then
         export PS1="\u@\h \w [dev]\$ "
     fi

... or to browse the profile:

     $ ls "$GUIX_ENVIRONMENT/bin"

Additionally, more than one package may be specified, in which case the union of the inputs for the given packages are used.  For example, the command below spawns a shell where all of the dependencies of both Guile and Emacs are available:

     guix environment guile emacs

Sometimes an interactive shell session is not desired.  An arbitrary command may be invoked by placing the -- token to separate the command from the rest of the arguments:

     guix environment guile -- make -j4

In other situations, it is more convenient to specify the list of packages needed in the environment.  For example, the following command runs python from an environment containing Python 2.7 and NumPy:

     guix environment --ad-hoc python2-numpy python-2.7 -- python

Furthermore, one might want the dependencies of a package and also some additional packages that are not build-time or runtime dependencies, but are useful when developing nonetheless.  Because of this, the --ad-hoc flag is positional.  Packages appearing before --ad-hoc are interpreted as packages whose dependencies will be added to the environment.  Packages appearing after are interpreted as packages that will be added to the environment directly.  For example, the following command creates a Guix development environment that additionally includes Git and strace:

     guix environment guix --ad-hoc git strace

Sometimes it is desirable to isolate the environment as much as possible, for maximal purity and reproducibility.  In particular, when using Guix on a host distro that is not GuixSD, it is desirable to prevent access to /usr/bin and other system-wide resources from the development environment.  For example, the following command spawns a Guile REPL in a ``container'' where only the store and the current working directory are mounted:

     guix environment --ad-hoc --container guile -- guile

     The --container option requires Linux-libre 3.19 or newer.

The available options are summarized below.

--expression=EXPR
-e EXPR
     Create an environment for the package or list of packages that EXPR evaluates to.

     For example, running:

          guix environment -e '(@ (gnu packages maths) petsc-openmpi)'

     starts a shell with the environment for this specific variant of the PETSc package.

     Running:

          guix environment --ad-hoc -e '(@ (gnu) %base-packages)'

     starts a shell with all the GuixSD base packages available.

     The above commands only the use default output of the given packages. To select other outputs, two element tuples can be specified:

          guix environment --ad-hoc -e '(list ( (gnu packages bash) bash) "include")'

--load=FILE
-l FILE
     Create an environment for the package or list of packages that the code within FILE evaluates to.

     As an example, FILE might contain a definition like this (see Defining Packages):

               [file environment-gdb.scm not included]

--ad-hoc
     Include all specified packages in the resulting environment, as if an ad hoc package were defined with them as inputs.  This option is useful for quickly creating an environment without having to write a package expression to contain the desired inputs.

     For instance, the command:

          guix environment --ad-hoc guile guile-sdl -- guile

     runs guile in an environment where Guile and Guile-SDL are available.

     Note that this example implicitly asks for the default output of guile and guile-sdl, but it is possible to ask for a specific output---e.g., glib:bin asks for the bin output of glib (see Packages with Multiple Outputs).

     This option may be composed with the default behavior of guix environment.  Packages appearing before --ad-hoc are interpreted as packages whose dependencies will be added to the environment, the default behavior.  Packages appearing after are interpreted as packages that will be added to the environment directly.

--pure
     Unset existing environment variables when building the new environment. This has the effect of creating an environment in which search paths only contain package inputs.

--search-paths
     Display the environment variable definitions that make up the environment.

--system=SYSTEM
-s SYSTEM
     Attempt to build for SYSTEM---e.g., i686-linux.

--container
-C
     Run COMMAND within an isolated container.  The current working directory outside the container is mapped inside the container. Additionally, a dummy home directory is created that matches the current user's home directory, and /etc/passwd is configured accordingly. The spawned process runs as the current user outside the container, but has root privileges in the context of the container.

--network
-N
     For containers, share the network namespace with the host system. Containers created without this flag only have access to the loopback device.

--expose=SOURCE[=TARGET]
     For containers, expose the file system SOURCE from the host system as the read-only file system TARGET within the container.  If TARGET is not specified, SOURCE is used as the target mount point in the container.

     The example below spawns a Guile REPL in a container in which the user's home directory is accessible read-only via the /exchange directory:

          guix environment --container --expose=$HOME=/exchange guile -- guile

--share=SOURCE[=TARGET]
     For containers, share the file system SOURCE from the host system as the writable file system TARGET within the container.  If TARGET is not specified, SOURCE is used as the target mount point in the container.

     The example below spawns a Guile REPL in a container in which the user's home directory is accessible for both reading and writing via the /exchange directory:

          guix environment --container --share=$HOME=/exchange guile -- guile

It also supports all of the common build options that guix build supports (see Common Build Options).

Invoking guix publish
=====================

The purpose of guix publish is to enable users to easily share their store with others, who can then use it as a substitute server (see Substitutes).

When guix publish runs, it spawns an HTTP server which allows anyone with network access to obtain substitutes from it.  This means that any machine running Guix can also act as if it were a build farm, since the HTTP interface is compatible with Hydra, the software behind the hydra.gnu.org build farm.

For security, each substitute is signed, allowing recipients to check their authenticity and integrity (see Substitutes).  Because guix publish uses the signing key of the system, which is only readable by the system administrator, it must be started as root; the --user option makes it drop root privileges early on.

The signing key pair must be generated before guix publish is launched, using guix archive --generate-key (see Invoking guix archive).

The general syntax is:

     guix publish OPTIONS...

Running guix publish without any additional arguments will spawn an HTTP server on port 8080:

     guix publish

Once a publishing server has been authorized (see Invoking guix archive), the daemon may download substitutes from it:

     guix-daemon --substitute-urls=http://example.org:8080

As a bonus, guix publish also serves as a content-addressed mirror for source files referenced in origin records (see origin Reference).  For instance, assuming guix publish is running on example.org, the following URL returns the raw hello-2.10.tar.gz file with the given SHA256 hash (represented in nix-base32 format, see Invoking guix hash):

     http://example.org/file/hello-2.10.tar.gz/sha256/0ssi1...ndq1i

Obviously, these URLs only work for files that are in the store; in other cases, they return 404 (``Not Found'').

The following options are available:

--port=PORT
-p PORT
     Listen for HTTP requests on PORT.

--listen=HOST
     Listen on the network interface for HOST.  The default is to accept connections from any interface.

--user=USER
-u USER
     Change privileges to USER as soon as possible---i.e., once the server socket is open and the signing key has been read.

--compression[=LEVEL]
-C [LEVEL]
     Compress data using the given LEVEL.  When LEVEL is zero, disable compression.  The range 1 to 9 corresponds to different gzip compression levels: 1 is the fastest, and 9 is the best (CPU-intensive). The default is 3.

     Compression occurs on the fly and the compressed streams are not cached.  Thus, to reduce load on the machine that runs guix publish, it may be a good idea to choose a low compression level, or to run guix publish behind a caching proxy.

--ttl=TTL
     Produce Cache-Control HTTP headers that advertise a time-to-live (TTL) of TTL.  TTL must denote a duration: 5d means 5 days, 1m means 1 month, and so on.

     This allows the user's Guix to keep substitute information in cache for TTL.  However, note that guix publish does not itself guarantee that the store items it provides will indeed remain available for as long as TTL.

--repl[=PORT]
-r [PORT]
     Spawn a Guile REPL server (see REPL Servers (GNU Guile Reference Manual)) on PORT (37146 by default).  This is used primarily for debugging a running guix publish server.

Enabling guix publish on a GuixSD system is a one-liner: just add a call to guix-publish-service in the services field of the operating-system declaration (see guix-publish-service).

If you are instead running Guix on a ``foreign distro'', follow these instructions:”

  * If your host distro uses the systemd init system:

          # ln -s ~root/.guix-profile/lib/systemd/system/guix-publish.service \
                  /etc/systemd/system/
          # systemctl start guix-publish && systemctl enable guix-publish

  * If your host distro uses the Upstart init system:

          # ln -s ~root/.guix-profile/lib/upstart/system/guix-publish.conf /etc/init/
          # start guix-publish

  * Otherwise, proceed similarly with your distro's init system.

Invoking guix challenge
=======================

Do the binaries provided by this server really correspond to the source code it claims to build?  Is a package build process deterministic? These are the questions the guix challenge command attempts to answer.

The former is obviously an important question: Before using a substitute server (see Substitutes), one had better verify that it provides the right binaries, and thus challenge it.  The latter is what enables the former: If package builds are deterministic, then independent builds of the package should yield the exact same result, bit for bit; if a server provides a binary different from the one obtained locally, it may be either corrupt or malicious.

We know that the hash that shows up in /gnu/store file names is the hash of all the inputs of the process that built the file or directory---compilers, libraries, build scripts, etc. (see Introduction).  Assuming deterministic build processes, one store file name should map to exactly one build output. guix challenge checks whether there is, indeed, a single mapping by comparing the build outputs of several independent builds of any given store item.

The command output looks like this:

     $ guix challenge --substitute-urls="https://hydra.gnu.org https://guix.example.org"
     updating list of substitutes from 'https://hydra.gnu.org'... 100.0%
     updating list of substitutes from 'https://guix.example.org'... 100.0%
     /gnu/store/...-openssl-1.0.2d contents differ:
       local hash: 0725l22r5jnzazaacncwsvp9kgf42266ayyp814v7djxs7nk963q
       https://hydra.gnu.org/nar/...-openssl-1.0.2d: 0725l22r5jnzazaacncwsvp9kgf42266ayyp814v7djxs7nk963q
       https://guix.example.org/nar/...-openssl-1.0.2d: 1zy4fmaaqcnjrzzajkdn3f5gmjk754b43qkq47llbyak9z0qjyim
     /gnu/store/...-git-2.5.0 contents differ:
       local hash: 00p3bmryhjxrhpn2gxs2fy0a15lnip05l97205pgbk5ra395hyha
       https://hydra.gnu.org/nar/...-git-2.5.0: 069nb85bv4d4a6slrwjdy8v1cn4cwspm3kdbmyb81d6zckj3nq9f
       https://guix.example.org/nar/...-git-2.5.0: 0mdqa9w1p6cmli6976v4wi0sw9r4p5prkj7lzfd1877wk11c9c73
     /gnu/store/...-pius-2.1.1 contents differ:
       local hash: 0k4v3m9z1zp8xzzizb7d8kjj72f9172xv078sq4wl73vnq9ig3ax
       https://hydra.gnu.org/nar/...-pius-2.1.1: 0k4v3m9z1zp8xzzizb7d8kjj72f9172xv078sq4wl73vnq9ig3ax
       https://guix.example.org/nar/...-pius-2.1.1: 1cy25x1a4fzq5rk0pmvc8xhwyffnqz95h2bpvqsz2mpvlbccy0gs

In this example, guix challenge first scans the store to determine the set of locally-built derivations---as opposed to store items that were downloaded from a substitute server---and then queries all the substitute servers.  It then reports those store items for which the servers obtained a result different from the local build.

As an example, guix.example.org always gets a different answer. Conversely, hydra.gnu.org agrees with local builds, except in the case of Git.  This might indicate that the build process of Git is non-deterministic, meaning that its output varies as a function of various things that Guix does not fully control, in spite of building packages in isolated environments (see Features).  Most common sources of non-determinism include the addition of timestamps in build results, the inclusion of random numbers, and directory listings sorted by inode number.  See https://reproducible-builds.org/docs/, for more information.

To find out what is wrong with this Git binary, we can do something along these lines (see Invoking guix archive):

     $ wget -q -O - https://hydra.gnu.org/nar/...-git-2.5.0 \
        | guix archive -x /tmp/git
     $ diff -ur --no-dereference /gnu/store/...-git.2.5.0 /tmp/git

This command shows the difference between the files resulting from the local build, and the files resulting from the build on hydra.gnu.org (see Comparing and Merging Files).  The diff command works great for text files.  When binary files differ, a better option is Diffoscope (https://diffoscope.org/), a tool that helps visualize differences for all kinds of files.

Once you have done that work, you can tell whether the differences are due to a non-deterministic build process or to a malicious server.  We try hard to remove sources of non-determinism in packages to make it easier to verify substitutes, but of course, this is a process that involves not just Guix, but a large part of the free software community. In the meantime, guix challenge is one tool to help address the problem.

If you are writing packages for Guix, you are encouraged to check whether hydra.gnu.org and other substitute servers obtain the same build result as you did with:

     $ guix challenge PACKAGE

where PACKAGE is a package specification such as guile@2.0 or glibc:debug.

The general syntax is:

     guix challenge OPTIONS [PACKAGES...]

When a difference is found between the hash of a locally-built item and that of a server-provided substitute, or among substitutes provided by different servers, the command displays it as in the example above and its exit code is 2 (other non-zero exit codes denote other kinds of errors.)

The one option that matters is:

--substitute-urls=URLS
     Consider URLS the whitespace-separated list of substitute source URLs to compare to.

Invoking guix container
=======================

     As of version VERSION, this tool is experimental.  The interface is subject to radical change in the future.

The purpose of guix container is to manipulate processes running within an isolated environment, commonly known as a ``container'', typically created by the guix environment (see Invoking guix environment) and guix system container (see Invoking guix system) commands.

The general syntax is:

     guix container ACTION OPTIONS...

ACTION specifies the operation to perform with a container, and OPTIONS specifies the context-specific arguments for the action.

The following actions are available:

exec
     Execute a command within the context of a running container.

     The syntax is:

          guix container exec PID PROGRAM ARGUMENTS...

     PID specifies the process ID of the running container. PROGRAM specifies an executable file name within the root file system of the container.  ARGUMENTS are the additional options that will be passed to PROGRAM.

     The following command launches an interactive login shell inside a GuixSD container, started by guix system container, and whose process ID is 9001:

          guix container exec 9001 /run/current-system/profile/bin/bash --login

     Note that the PID cannot be the parent process of a container.  It must be PID 1 of the container or one of its child processes.

GNU Distribution
****************

Guix comes with a distribution of the GNU system consisting entirely of free software (The term ``free'' here refers to the freedom provided to users of that software (http://www.gnu.org/philosophy/free-sw.html).).  The distribution can be installed on its own (see System Installation), but it is also possible to install Guix as a package manager on top of an installed GNU/Linux system (see Installation).  To distinguish between the two, we refer to the standalone distribution as the Guix System Distribution, or GuixSD.

The distribution provides core GNU packages such as GNU libc, GCC, and Binutils, as well as many GNU and non-GNU applications.  The complete list of available packages can be browsed on-line (http://www.gnu.org/software/guix/packages) or by running guix package (see Invoking guix package):

     guix package --list-available

Our goal is to provide a practical 100% free software distribution of Linux-based and other variants of GNU, with a focus on the promotion and tight integration of GNU components, and an emphasis on programs and tools that help users exert that freedom.

Packages are currently available on the following platforms:

x86_64-linux
     Intel/AMD x86_64 architecture, Linux-Libre kernel;

i686-linux
     Intel 32-bit architecture (IA32), Linux-Libre kernel;

armhf-linux
     ARMv7-A architecture with hard float, Thumb-2 and NEON, using the EABI hard-float application binary interface (ABI), and Linux-Libre kernel.

mips64el-linux
     little-endian 64-bit MIPS processors, specifically the Loongson series, n32 ABI, and Linux-Libre kernel.

GuixSD itself is currently only available on i686 and x86_64.

For information on porting to other architectures or kernels, see Porting.

Building this distribution is a cooperative effort, and you are invited to join!  See Contributing, for information about how you can help.

System Installation
===================

This section explains how to install the Guix System Distribution (GuixSD) on a machine.  The Guix package manager can also be installed on top of a running GNU/Linux system, see Installation.

     You are reading this documentation with an Info reader.  For details on how to use it, hit the RET key (``return'' or ``enter'') on the link that follows: see Info reader (Stand-alone GNU Info).  Hit l afterwards to come back here.

     Alternately, run info info in another tty to keep the manual available.

Limitations
-----------

As of version VERSION, the Guix System Distribution (GuixSD) is not production-ready.  It may contain bugs and lack important features.  Thus, if you are looking for a stable production system that respects your freedom as a computer user, a good solution at this point is to consider one of the more established GNU/Linux distributions (http://www.gnu.org/distros/free-distros.html).  We hope you can soon switch to the GuixSD without fear, of course.  In the meantime, you can also keep using your distribution and try out the package manager on top of it (see Installation).

Before you proceed with the installation, be aware of the following noteworthy limitations applicable to version VERSION:

  * The installation process does not include a graphical user interface and requires familiarity with GNU/Linux (see the following subsections to get a feel of what that means.)

  * Support for the Logical Volume Manager (LVM) is missing.

  * Few system services are currently supported out-of-the-box (see Services).

  * More than 4,000 packages are available, but you may occasionally find that a useful package is missing.

  * GNOME, Xfce, and Enlightenment are available (see Desktop Services), as well as a number of X11 window managers.  However, some graphical applications may be missing, as well as KDE.

You have been warned!  But more than a disclaimer, this is an invitation to report issues (and success stories!), and to join us in improving it. See Contributing, for more info.

Hardware Considerations
-----------------------

GNU GuixSD focuses on respecting the user's computing freedom.  It builds around the kernel Linux-libre, which means that only hardware for which free software drivers and firmware exist is supported.  Nowadays, a wide range of off-the-shelf hardware is supported on GNU/Linux-libre---from keyboards to graphics cards to scanners and Ethernet controllers.  Unfortunately, there are still areas where hardware vendors deny users control over their own computing, and such hardware is not supported on GuixSD.

One of the main areas where free drivers or firmware are lacking is WiFi devices.  WiFi devices known to work include those using Atheros chips (AR9271 and AR7010), which corresponds to the ath9k Linux-libre driver, and those using Broadcom/AirForce chips (BCM43xx with Wireless-Core Revision 5), which corresponds to the b43-open Linux-libre driver.  Free firmware exists for both and is available out-of-the-box on GuixSD, as part of %BASE-FIRMWARE (see firmware).

The Free Software Foundation (https://www.fsf.org/) runs Respects Your Freedom (https://www.fsf.org/ryf) (RYF), a certification program for hardware products that respect your freedom and your privacy and ensure that you have control over your device.  We encourage you to check the list of RYF-certified devices.

Another useful resource is the H-Node (https://www.h-node.org/) web site.  It contains a catalog of hardware devices with information about their support in GNU/Linux.

USB Stick Installation
----------------------

An installation image for USB sticks can be downloaded from ftp://alpha.gnu.org/gnu/guix/guixsd-usb-install-VERSION.SYSTEM.xz, where SYSTEM is one of:

x86_64-linux
     for a GNU/Linux system on Intel/AMD-compatible 64-bit CPUs;

i686-linux
     for a 32-bit GNU/Linux system on Intel-compatible CPUs.

Make sure to download the associated .sig file and to verify the authenticity of the image against it, along these lines:

     $ wget ftp://alpha.gnu.org/gnu/guix/guixsd-usb-install-VERSION.SYSTEM.xz.sig
     $ gpg --verify guixsd-usb-install-VERSION.SYSTEM.xz.sig

If that command fails because you do not have the required public key, then run this command to import it:

     $ gpg --keyserver pgp.mit.edu --recv-keys 3CE464558A84FDC69DB40CFB090B11993D9AEBB5

and rerun the gpg --verify command.

This image contains a single partition with the tools necessary for an installation.  It is meant to be copied as is to a large-enough USB stick.

To copy the image to a USB stick, follow these steps:

 1. Decompress the image using the xz command:

          xz -d guixsd-usb-install-VERSION.SYSTEM.xz

 2. Insert a USB stick of 1 GiB or more into your machine, and determine its device name.  Assuming that the USB stick is known as /dev/sdX, copy the image with:

          dd if=guixsd-usb-install-VERSION.x86_64 of=/dev/sdX

     Access to /dev/sdX usually requires root privileges.

Once this is done, you should be able to reboot the system and boot from the USB stick.  The latter usually requires you to get in the BIOS' boot menu, where you can choose to boot from the USB stick.

See Installing GuixSD in a VM, if, instead, you would like to install GuixSD in a virtual machine (VM).

Preparing for Installation
--------------------------

Once you have successfully booted the image on the USB stick, you should end up with a root prompt.  Several console TTYs are configured and can be used to run commands as root.  TTY2 shows this documentation, browsable using the Info reader commands (see Stand-alone GNU Info).  The installation system runs the GPM mouse daemon, which allows you to select text with the left mouse button and to paste it with the middle button.

     Installation requires access to the Internet so that any missing dependencies of your system configuration can be downloaded.  See the ``Networking'' section below.

The installation system includes many common tools needed for this task. But it is also a full-blown GuixSD system, which means that you can install additional packages, should you need it, using guix package (see Invoking guix package).

Keyboard Layout
...............

The installation image uses the US qwerty keyboard layout.  If you want to change it, you can use the loadkeys command.  For example, the following command selects the Dvorak keyboard layout:

     loadkeys dvorak

See the files under /run/current-system/profile/share/keymaps for a list of available keyboard layouts.  Run man loadkeys for more information.

Networking
..........

Run the following command see what your network interfaces are called:

     ifconfig -a

... or, using the GNU/Linux-specific ip command:

     ip a

Wired interfaces have a name starting with e; for example, the interface corresponding to the first on-board Ethernet controller is called eno1.  Wireless interfaces have a name starting with w, like w1p2s0.

Wired connection
     To configure a wired network run the following command, substituting INTERFACE with the name of the wired interface you want to use.

          ifconfig INTERFACE up

Wireless connection
     To configure wireless networking, you can create a configuration file for the wpa_supplicant configuration tool (its location is not important) using one of the available text editors such as zile:

          zile wpa_supplicant.conf

     As an example, the following stanza can go to this file and will work for many wireless networks, provided you give the actual SSID and passphrase for the network you are connecting to:

          network={
            ssid="MY-SSID"
            key_mgmt=WPA-PSK
            psk="the network's secret passphrase"
          }

     Start the wireless service and run it in the background with the following command (substitute INTERFACE with the name of the network interface you want to use):

          wpa_supplicant -c wpa_supplicant.conf -i INTERFACE -B

     Run man wpa_supplicant for more information.

At this point, you need to acquire an IP address.  On a network where IP addresses are automatically assigned via DHCP, you can run:

     dhclient -v INTERFACE

Try to ping a server to see if networking is up and running:

     ping -c 3 gnu.org

Setting up network access is almost always a requirement because the image does not contain all the software and tools that may be needed.

Disk Partitioning
.................

Unless this has already been done, the next step is to partition, and then format the target partition(s).

The installation image includes several partitioning tools, including Parted (see Overview (GNU Parted User Manual)), fdisk, and cfdisk.  Run it and set up your disk with the partition layout you want:

     cfdisk

Once you are done partitioning the target hard disk drive, you have to create a file system on the relevant partition(s) (Currently GuixSD pretty much assumes an ext4 file system.  In particular, code that reads partition UUIDs and labels only works with ext4.  This will be fixed in the future.).

Preferably, assign partitions a label so that you can easily and reliably refer to them in file-system declarations (see File Systems).  This is typically done using the -L option of mkfs.ext4 and related commands.  So, assuming the target root partition lives at /dev/sda1, a file system with the label my-root can be created with:

     mkfs.ext4 -L my-root /dev/sda1

If you are instead planning to encrypt the root partition, you can use the Cryptsetup/LUKS utilities to do that (see man cryptsetup for more information.)  Assuming you want to store the root partition on /dev/sda1, the command sequence would be along these lines:

     cryptsetup luksFormat /dev/sda1
     cryptsetup open --type luks /dev/sda1 my-partition
     mkfs.ext4 -L my-root /dev/mapper/my-partition

Once that is done, mount the target root partition under /mnt with a command like (again, assuming my-root is the label of the root partition):

     mount LABEL=my-root /mnt

Finally, if you plan to use one or more swap partitions (see swap space (The GNU C Library Reference Manual)), make sure to initialize them with mkswap.  Assuming you have one swap partition on /dev/sda2, you would run:

     mkswap /dev/sda2
     swapon /dev/sda2

Proceeding with the Installation
--------------------------------

With the target partitions ready and the target root mounted on /mnt, we're ready to go.  First, run:

     herd start cow-store /mnt

This makes /gnu/store copy-on-write, such that packages added to it during the installation phase are written to the target disk on /mnt rather than kept in memory.  This is necessary because the first phase of the guix system init command (see below) entails downloads or builds to /gnu/store which, initially, is an in-memory file system.

Next, you have to edit a file and provide the declaration of the operating system to be installed.  To that end, the installation system comes with three text editors: GNU nano (see GNU nano Manual), GNU Zile (an Emacs clone), and nvi (a clone of the original BSD vi editor). We strongly recommend storing that file on the target root file system, say, as /mnt/etc/config.scm.  Failing to do that, you will have lost your configuration file once you have rebooted into the newly-installed system.

See Using the Configuration System, for an overview of the configuration file.  The example configurations discussed in that section are available under /etc/configuration in the installation image.  Thus, to get started with a system configuration providing a graphical display server (a ``desktop'' system), you can run something along these lines:

     # mkdir /mnt/etc
     # cp /etc/configuration/desktop.scm /mnt/etc/config.scm
     # zile /mnt/etc/config.scm

You should pay attention to what your configuration file contains, and in particular:

  * Make sure the grub-configuration form refers to the device you want to install GRUB on.

  * Be sure that your partition labels match the value of their respective device fields in your file-system configuration, assuming your file-system configuration sets the value of title to 'label.

  * If there are encrypted or RAID partitions, make sure to add a mapped-devices field to describe them (see Mapped Devices).

Once you are done preparing the configuration file, the new system must be initialized (remember that the target root file system is mounted under /mnt):

     guix system init /mnt/etc/config.scm /mnt

This copies all the necessary files and installs GRUB on /dev/sdX, unless you pass the --no-grub option.  For more information, see Invoking guix system.  This command may trigger downloads or builds of missing packages, which can take some time.

Once that command has completed---and hopefully succeeded!---you can run reboot and boot into the new system.  The root password in the new system is initially empty; other users' passwords need to be initialized by running the passwd command as root, unless your configuration specifies otherwise (see user account passwords).

Join us on #guix on the Freenode IRC network or on guix-devel@gnu.org to share your experience---good or not so good.

Installing GuixSD in a Virtual Machine
--------------------------------------

If you'd like to install GuixSD in a virtual machine (VM) rather than on your beloved machine, this section is for you.

To boot a QEMU (http://qemu.org/) VM for installing GuixSD in a disk image, follow these steps:

 1. First, retrieve the GuixSD installation image as described previously (see USB Stick Installation).

 2. Create a disk image that will hold the installed system.  To make a qcow2-formatted disk image, use the qemu-img command:

          qemu-img create -f qcow2 guixsd.img 5G

     This will create a 5GB file.

 3. Boot the USB installation image in an VM:

          qemu-system-x86_64 -m 1024 -smp 1 \
            -net default -net nic,model=virtio -boot menu=on \
            -drive file=guixsd.img \
            -drive file=guixsd-usb-install-VERSION.SYSTEM

     In the VM console, quickly press the F12 key to enter the boot menu.  Then press the 2 key and the RET key to validate your selection.

 4. You're now root in the VM, proceed with the installation process. See Preparing for Installation, and follow the instructions.

Once installation is complete, you can boot the system that's on your guixsd.img image.  See Running GuixSD in a VM, for how to do that.

Building the Installation Image
-------------------------------

The installation image described above was built using the guix system command, specifically:

     guix system disk-image --image-size=1G gnu/system/install.scm

Have a look at gnu/system/install.scm in the source tree, and see also Invoking guix system for more information about the installation image.

System Configuration
====================

The Guix System Distribution supports a consistent whole-system configuration mechanism.  By that we mean that all aspects of the global system configuration---such as the available system services, timezone and locale settings, user accounts---are declared in a single place.  Such a system configuration can be instantiated---i.e., effected.

One of the advantages of putting all the system configuration under the control of Guix is that it supports transactional system upgrades, and makes it possible to roll back to a previous system instantiation, should something go wrong with the new one (see Features).  Another advantage is that it makes it easy to replicate the exact same configuration across different machines, or at different points in time, without having to resort to additional administration tools layered on top of the own tools of the system.

This section describes this mechanism.  First we focus on the system administrator's viewpoint---explaining how the system is configured and instantiated.  Then we show how this mechanism can be extended, for instance to support new system services.

Using the Configuration System
------------------------------

The operating system is configured by providing an operating-system declaration in a file that can then be passed to the guix system command (see Invoking guix system).  A simple setup, with the default system services, the default Linux-Libre kernel, initial RAM disk, and boot loader looks like this:

          [file os-config-bare-bones.texi not included]

This example should be self-describing.  Some of the fields defined above, such as host-name and bootloader, are mandatory. Others, such as packages and services, can be omitted, in which case they get a default value.

Below we discuss the effect of some of the most important fields (see operating-system Reference, for details about all the available fields), and how to instantiate the operating system using guix system.

Globally-Visible Packages
.........................

The packages field lists packages that will be globally visible on the system, for all user accounts---i.e., in every user's PATH environment variable---in addition to the per-user profiles (see Invoking guix package).  The %BASE-PACKAGES variable provides all the tools one would expect for basic user and administrator tasks---including the GNU Core Utilities, the GNU Networking Utilities, the GNU Zile lightweight text editor, find, grep, etc.  The example above adds tcpdump to those, taken from the (gnu packages admin) module (see Package Modules).

Referring to packages by variable name, like TCPDUMP above, has the advantage of being unambiguous; it also allows typos and such to be diagnosed right away as ``unbound variables''.  The downside is that one needs to know which module defines which package, and to augment the use-package-modules line accordingly.  To avoid that, one can use the specification->package procedure of the (gnu packages) module, which returns the best package for a given name or name and version:

     (use-modules (gnu packages))

     (operating-system
       ;; ...
       (packages (append (map specification->package
                              '("tcpdump" "htop" "gnupg@2.0"))
                         %base-packages)))

System Services
...............

The services field lists system services to be made available when the system starts (see Services). The operating-system declaration above specifies that, in addition to the basic services, we want the lshd secure shell daemon listening on port 2222 (see lsh-service).  Under the hood, lsh-service arranges so that lshd is started with the right command-line options, possibly with supporting configuration files generated as needed (see Defining Services).

Occasionally, instead of using the base services as is, you will want to customize them.  To do this, use modify-services (see modify-services) to modify the list.

For example, suppose you want to modify guix-daemon and Mingetty (the console log-in) in the %BASE-SERVICES list (see %base-services).  To do that, you can write the following in your operating system declaration:

     (define %my-services
       ;; My very own list of services.
       (modify-services %base-services
         (guix-service-type config =>
                            (guix-configuration
                             (inherit config)
                             (use-substitutes? #f)
                             (extra-options '("--gc-keep-derivations"))))
         (mingetty-service-type config =>
                                (mingetty-configuration
                                 (inherit config)))))

     (operating-system
       ;; ...
       (services %my-services))

This changes the configuration---i.e., the service parameters---of the guix-service-type instance, and that of all the mingetty-service-type instances in the %BASE-SERVICES list. Observe how this is accomplished: first, we arrange for the original configuration to be bound to the identifier config in the BODY, and then we write the BODY so that it evaluates to the desired configuration.  In particular, notice how we use inherit to create a new configuration which has the same values as the old configuration, but with a few modifications.

The configuration for a typical ``desktop'' usage, with an encrypted root partition, the X11 display server, GNOME and Xfce (users can choose which of these desktop environments to use at the log-in screen by pressing F1), network management, power management, and more, would look like this:

          [file os-config-desktop.texi not included]

A graphical environment with a choice of lightweight window managers instead of full-blown desktop environments would look like this:

          [file os-config-lightweight-desktop.texi not included]

See Desktop Services, for the exact list of services provided by %DESKTOP-SERVICES.  See X.509 Certificates, for background information about the nss-certs package that is used here.

Again, %DESKTOP-SERVICES is just a list of service objects.  If you want to remove services from there, you can do so using the procedures for list filtering (see SRFI-1 Filtering and Partitioning (GNU Guile Reference Manual)).  For instance, the following expression returns a list that contains all the services in %DESKTOP-SERVICES minus the Avahi service:

     (remove (lambda (service)
               (eq? (service-kind service) avahi-service-type))
             %desktop-services)

Instantiating the System
........................

Assuming the operating-system declaration is stored in the my-system-config.scm file, the guix system reconfigure my-system-config.scm command instantiates that configuration, and makes it the default GRUB boot entry (see Invoking guix system).

The normal way to change the system configuration is by updating this file and re-running guix system reconfigure.  One should never have to touch files in /etc or to run commands that modify the system state such as useradd or grub-install.  In fact, you must avoid that since that would not only void your warranty but also prevent you from rolling back to previous versions of your system, should you ever need to.

Speaking of roll-back, each time you run guix system reconfigure, a new generation of the system is created---without modifying or deleting previous generations.  Old system generations get an entry in the GRUB boot menu, allowing you to boot them in case something went wrong with the latest generation.  Reassuring, no?  The guix system list-generations command lists the system generations available on disk.  It is also possible to roll back the system via the commands guix system roll-back and guix system switch-generation.

Although the command guix system reconfigure will not modify previous generations, must take care when the current generation is not the latest (e.g., after invoking guix system roll-back), since the operation might overwrite a later generation (see Invoking guix system).

The Programming Interface
.........................

At the Scheme level, the bulk of an operating-system declaration is instantiated with the following monadic procedure (see The Store Monad):

 -- Monadic Procedure: operating-system-derivation os
     Return a derivation that builds OS, an operating-system object (see Derivations).

     The output of the derivation is a single directory that refers to all the packages, configuration files, and other supporting files needed to instantiate OS.

This procedure is provided by the (gnu system) module.  Along with (gnu services) (see Services), this module contains the guts of GuixSD.  Make sure to visit it!

operating-system Reference
--------------------------

This section summarizes all the options available in operating-system declarations (see Using the Configuration System).

 -- Data Type: operating-system
     This is the data type representing an operating system configuration. By that, we mean all the global system configuration, not per-user configuration (see Using the Configuration System).

     kernel (default: LINUX-LIBRE)
          The package object of the operating system kernel to use (Currently only the Linux-libre kernel is supported.  In the future, it will be possible to use the GNU Hurd.).

     kernel-arguments (default: '())
          List of strings or gexps representing additional arguments to pass on the command-line of the kernel---e.g., ("console=ttyS0").

     bootloader
          The system bootloader configuration object.  See GRUB Configuration.

     initrd (default: base-initrd)
          A two-argument monadic procedure that returns an initial RAM disk for the Linux kernel.  See Initial RAM Disk.

     firmware (default: %BASE-FIRMWARE)
          List of firmware packages loadable by the operating system kernel.

          The default includes firmware needed for Atheros- and Broadcom-based WiFi devices (Linux-libre modules ath9k and b43-open, respectively).  See Hardware Considerations, for more info on supported hardware.

     host-name
          The host name.

     hosts-file
          A file-like object (see file-like objects) for use as /etc/hosts (see Host Names (The GNU C Library Reference Manual)).  The default is a file with entries for localhost and HOST-NAME.

     mapped-devices (default: '())
          A list of mapped devices.  See Mapped Devices.

     file-systems
          A list of file systems.  See File Systems.

     swap-devices (default: '())
          A list of strings identifying devices to be used for ``swap space'' (see Memory Concepts (The GNU C Library Reference Manual)). For example, '("/dev/sda3").

     users (default: %base-user-accounts)
     groups (default: %BASE-GROUPS)
          List of user accounts and groups.  See User Accounts.

     skeletons (default: (default-skeletons))
          A list target file name/file-like object tuples (see file-like objects).  These are the skeleton files that will be added to the home directory of newly-created user accounts.

          For instance, a valid value may look like this:

               `((".bashrc" ,(plain-file "bashrc" "echo Hello\n"))
                 (".guile" ,(plain-file "guile"
                                        "(use-modules (ice-9 readline))
                                         (activate-readline)")))

     issue (default: %DEFAULT-ISSUE)
          A string denoting the contents of the /etc/issue file, which is displayed when users log in on a text console.

     packages (default: %BASE-PACKAGES)
          The set of packages installed in the global profile, which is accessible at /run/current-system/profile.

          The default set includes core utilities and it is good practice to install non-core utilities in user profiles (see Invoking guix package).

     timezone
          A timezone identifying string---e.g., "Europe/Paris".

          You can run the tzselect command to find out which timezone string corresponds to your region.  Choosing an invalid timezone name causes guix system to fail.

     locale (default: "en_US.utf8")
          The name of the default locale (see Locale Names (The GNU C Library Reference Manual)).  See Locales, for more information.

     locale-definitions (default: %DEFAULT-LOCALE-DEFINITIONS)
          The list of locale definitions to be compiled and that may be used at run time.  See Locales.

     locale-libcs (default: (list GLIBC))
          The list of GNU libc packages whose locale data and tools are used to build the locale definitions.  See Locales, for compatibility considerations that justify this option.

     name-service-switch (default: %DEFAULT-NSS)
          Configuration of the libc name service switch (NSS)---a <name-service-switch> object.  See Name Service Switch, for details.

     services (default: %BASE-SERVICES)
          A list of service objects denoting system services.  See Services.

     pam-services (default: (base-pam-services))
          Linux pluggable authentication module (PAM) services.

     setuid-programs (default: %SETUID-PROGRAMS)
          List of string-valued G-expressions denoting setuid programs. See Setuid Programs.

     sudoers-file (default: %SUDOERS-SPECIFICATION)
          The contents of the /etc/sudoers file as a file-like object (see local-file and plain-file).

          This file specifies which users can use the sudo command, what they are allowed to do, and what privileges they may gain.  The default is that only root and members of the wheel group may use sudo.

File Systems
------------

The list of file systems to be mounted is specified in the file-systems field of the operating system declaration (see Using the Configuration System).  Each file system is declared using the file-system form, like this:

     (file-system
       (mount-point "/home")
       (device "/dev/sda3")
       (type "ext4"))

As usual, some of the fields are mandatory---those shown in the example above---while others can be omitted.  These are described below.

 -- Data Type: file-system
     Objects of this type represent file systems to be mounted.  They contain the following members:

     type
          This is a string specifying the type of the file system---e.g., "ext4".

     mount-point
          This designates the place where the file system is to be mounted.

     device
          This names the ``source'' of the file system.  By default it is the name of a node under /dev, but its meaning depends on the title field described below.

     title (default: 'device)
          This is a symbol that specifies how the device field is to be interpreted.

          When it is the symbol device, then the device field is interpreted as a file name; when it is label, then device is interpreted as a partition label name; when it is uuid, device is interpreted as a partition unique identifier (UUID).

          UUIDs may be converted from their string representation (as shown by the tune2fs -l command) using the uuid form (The uuid form expects 16-byte UUIDs as defined in RFC 4122 (https://tools.ietf.org/html/rfc4122).  This is the form of UUID used by the ext2 family of file systems and others, but it is different from ``UUIDs'' found in FAT file systems, for instance.), like this:

               (file-system
                 (mount-point "/home")
                 (type "ext4")
                 (title 'uuid)
                 (device (uuid "4dab5feb-d176-45de-b287-9b0a6e4c01cb")))

          The label and uuid options offer a way to refer to disk partitions without having to hard-code their actual device name (Note that, while it is tempting to use /dev/disk/by-uuid and similar device names to achieve the same result, this is not recommended: These special device nodes are created by the udev daemon and may be unavailable at the time the device is mounted.).

          However, when the source of a file system is a mapped device (see Mapped Devices), its device field must refer to the mapped device name---e.g., /dev/mapper/root-partition---and consequently title must be set to 'device.  This is required so that the system knows that mounting the file system depends on having the corresponding device mapping established.

     flags (default: '())
          This is a list of symbols denoting mount flags.  Recognized flags include read-only, bind-mount, no-dev (disallow access to special files), no-suid (ignore setuid and setgid bits), and no-exec (disallow program execution.)

     options (default: #f)
          This is either #f, or a string denoting mount options.

     mount? (default: #t)
          This value indicates whether to automatically mount the file system when the system is brought up.  When set to #f, the file system gets an entry in /etc/fstab (read by the mount command) but is not automatically mounted.

     needed-for-boot? (default: #f)
          This Boolean value indicates whether the file system is needed when booting.  If that is true, then the file system is mounted when the initial RAM disk (initrd) is loaded.  This is always the case, for instance, for the root file system.

     check? (default: #t)
          This Boolean indicates whether the file system needs to be checked for errors before being mounted.

     create-mount-point? (default: #f)
          When true, the mount point is created if it does not exist yet.

     dependencies (default: '())
          This is a list of <file-system> or <mapped-device> objects representing file systems that must be mounted or mapped devices that must be opened before (and unmounted or closed after) this one.

          As an example, consider a hierarchy of mounts: /sys/fs/cgroup is a dependency of /sys/fs/cgroup/cpu and /sys/fs/cgroup/memory.

          Another example is a file system that depends on a mapped device, for example for an encrypted partition (see Mapped Devices).

The (gnu system file-systems) exports the following useful variables.

 -- Scheme Variable: %base-file-systems
     These are essential file systems that are required on normal systems, such as %PSEUDO-TERMINAL-FILE-SYSTEM and %IMMUTABLE-STORE (see below.)  Operating system declarations should always contain at least these.

 -- Scheme Variable: %pseudo-terminal-file-system
     This is the file system to be mounted as /dev/pts.  It supports pseudo-terminals created via openpty and similar functions (see Pseudo-Terminals (The GNU C Library Reference Manual)).  Pseudo-terminals are used by terminal emulators such as xterm.

 -- Scheme Variable: %shared-memory-file-system
     This file system is mounted as /dev/shm and is used to support memory sharing across processes (see shm_open (The GNU C Library Reference Manual)).

 -- Scheme Variable: %immutable-store
     This file system performs a read-only ``bind mount'' of /gnu/store, making it read-only for all the users including root.  This prevents against accidental modification by software running as root or by system administrators.

     The daemon itself is still able to write to the store: it remounts it read-write in its own ``name space.''

 -- Scheme Variable: %binary-format-file-system
     The binfmt_misc file system, which allows handling of arbitrary executable file types to be delegated to user space.  This requires the binfmt.ko kernel module to be loaded.

 -- Scheme Variable: %fuse-control-file-system
     The fusectl file system, which allows unprivileged users to mount and unmount user-space FUSE file systems.  This requires the fuse.ko kernel module to be loaded.

Mapped Devices
--------------

The Linux kernel has a notion of device mapping: a block device, such as a hard disk partition, can be mapped into another device, usually in /dev/mapper/, with additional processing over the data that flows through it (Note that the GNU Hurd makes no difference between the concept of a ``mapped device'' and that of a file system: both boil down to translating input/output operations made on a file to operations on its backing store.  Thus, the Hurd implements mapped devices, like file systems, using the generic translator mechanism (see Translators (The GNU Hurd Reference Manual)).).  A typical example is encryption device mapping: all writes to the mapped device are encrypted, and all reads are deciphered, transparently. Guix extends this notion by considering any device or set of devices that are transformed in some way to create a new device; for instance, RAID devices are obtained by assembling several other devices, such as hard disks or partitions, into a new one that behaves as one partition. Other examples, not yet implemented, are LVM logical volumes.

Mapped devices are declared using the mapped-device form, defined as follows; for examples, see below.

 -- Data Type: mapped-device
     Objects of this type represent device mappings that will be made when the system boots up.

     source
          This is either a string specifying the name of the block device to be mapped, such as "/dev/sda3", or a list of such strings when several devices need to be assembled for creating a new one.

     target
          This string specifies the name of the resulting mapped device.  For kernel mappers such as encrypted devices of type luks-device-mapping, specifying "my-partition" leads to the creation of the "/dev/mapper/my-partition" device. For RAID devices of type raid-device-mapping, the full device name such as "/dev/md0" needs to be given.

     type
          This must be a mapped-device-kind object, which specifies how SOURCE is mapped to TARGET.

 -- Scheme Variable: luks-device-mapping
     This defines LUKS block device encryption using the cryptsetup command from the package with the same name.  It relies on the dm-crypt Linux kernel module.

 -- Scheme Variable: raid-device-mapping
     This defines a RAID device, which is assembled using the mdadm command from the package with the same name.  It requires a Linux kernel module for the appropriate RAID level to be loaded, such as raid456 for RAID-4, RAID-5 or RAID-6, or raid10 for RAID-10.

The following example specifies a mapping from /dev/sda3 to /dev/mapper/home using LUKS---the Linux Unified Key Setup (https://gitlab.com/cryptsetup/cryptsetup), a standard mechanism for disk encryption. The /dev/mapper/home device can then be used as the device of a file-system declaration (see File Systems).

     (mapped-device
       (source "/dev/sda3")
       (target "home")
       (type luks-device-mapping))

Alternatively, to become independent of device numbering, one may obtain the LUKS UUID (unique identifier) of the source device by a command like:

     cryptsetup luksUUID /dev/sda3

and use it as follows:

     (mapped-device
       (source (uuid "cb67fc72-0d54-4c88-9d4b-b225f30b0f44"))
       (target "home")
       (type luks-device-mapping))

A RAID device formed of the partitions /dev/sda1 and /dev/sdb1 may be declared as follows:

     (mapped-device
       (source (list "/dev/sda1" "/dev/sdb1"))
       (target "/dev/md0")
       (type raid-device-mapping))

The /dev/md0 device can then be used as the device of a file-system declaration (see File Systems). Note that the RAID level need not be given; it is chosen during the initial creation and formatting of the RAID device and is determined automatically later.

User Accounts
-------------

User accounts and groups are entirely managed through the operating-system declaration.  They are specified with the user-account and user-group forms:

     (user-account
       (name "alice")
       (group "users")
       (supplementary-groups '("wheel"   ;allow use of sudo, etc.
                               "audio"   ;sound card
                               "video"   ;video devices such as webcams
                               "cdrom")) ;the good ol' CD-ROM
       (comment "Bob's sister")
       (home-directory "/home/alice"))

When booting or upon completion of guix system reconfigure, the system ensures that only the user accounts and groups specified in the operating-system declaration exist, and with the specified properties.  Thus, account or group creations or modifications made by directly invoking commands such as useradd are lost upon reconfiguration or reboot.  This ensures that the system remains exactly as declared.

 -- Data Type: user-account
     Objects of this type represent user accounts.  The following members may be specified:

     name
          The name of the user account.

     group
          This is the name (a string) or identifier (a number) of the user group this account belongs to.

     supplementary-groups (default: '())
          Optionally, this can be defined as a list of group names that this account belongs to.

     uid (default: #f)
          This is the user ID for this account (a number), or #f.  In the latter case, a number is automatically chosen by the system when the account is created.

     comment (default: "")
          A comment about the account, such as the account owner's full name.

     home-directory
          This is the name of the home directory for the account.

     create-home-directory? (default: #t)
          Indicates whether the home directory of this account should be created if it does not exist yet.

     shell (default: Bash)
          This is a G-expression denoting the file name of a program to be used as the shell (see G-Expressions).

     system? (default: #f)
          This Boolean value indicates whether the account is a ``system'' account.  System accounts are sometimes treated specially; for instance, graphical login managers do not list them.

     password (default: #f)
          You would normally leave this field to #f, initialize user passwords as root with the passwd command, and then let users change it with passwd.  Passwords set with passwd are of course preserved across reboot and reconfiguration.

          If you do want to have a preset password for an account, then this field must contain the encrypted password, as a string. See crypt (The GNU C Library Reference Manual), for more information on password encryption, and Encryption (GNU Guile Reference Manual), for information on Guile's crypt procedure.

User group declarations are even simpler:

     (user-group (name "students"))

 -- Data Type: user-group
     This type is for, well, user groups.  There are just a few fields:

     name
          The name of the group.

     id (default: #f)
          The group identifier (a number).  If #f, a new number is automatically allocated when the group is created.

     system? (default: #f)
          This Boolean value indicates whether the group is a ``system'' group. System groups have low numerical IDs.

     password (default: #f)
          What, user groups can have a password?  Well, apparently yes.  Unless #f, this field specifies the password of the group.

For convenience, a variable lists all the basic user groups one may expect:

 -- Scheme Variable: %base-groups
     This is the list of basic user groups that users and/or packages expect to be present on the system.  This includes groups such as ``root'', ``wheel'', and ``users'', as well as groups used to control access to specific devices such as ``audio'', ``disk'', and ``cdrom''.

 -- Scheme Variable: %base-user-accounts
     This is the list of basic system accounts that programs may expect to find on a GNU/Linux system, such as the ``nobody'' account.

     Note that the ``root'' account is not included here.  It is a special-case and is automatically added whether or not it is specified.

Locales
-------

A locale defines cultural conventions for a particular language and region of the world (see Locales (The GNU C Library Reference Manual)).  Each locale has a name that typically has the form LANGUAGE_TERRITORY.CODESET---e.g., fr_LU.utf8 designates the locale for the French language, with cultural conventions from Luxembourg, and using the UTF-8 encoding.

Usually, you will want to specify the default locale for the machine using the locale field of the operating-system declaration (see locale).

The selected locale is automatically added to the locale definitions known to the system if needed, with its codeset inferred from its name---e.g., bo_CN.utf8 will be assumed to use the UTF-8 codeset.  Additional locale definitions can be specified in the locale-definitions slot of operating-system---this is useful, for instance, if the codeset could not be inferred from the locale name.  The default set of locale definitions includes some widely used locales, but not all the available locales, in order to save space.

For instance, to add the North Frisian locale for Germany, the value of that field may be:

     (cons (locale-definition
             (name "fy_DE.utf8") (source "fy_DE"))
           %default-locale-definitions)

Likewise, to save space, one might want locale-definitions to list only the locales that are actually used, as in:

     (list (locale-definition
             (name "ja_JP.eucjp") (source "ja_JP")
             (charset "EUC-JP")))

The compiled locale definitions are available at /run/current-system/locale/X.Y, where X.Y is the libc version, which is the default location where the GNU libc provided by Guix looks for locale data.  This can be overridden using the LOCPATH environment variable (see LOCPATH and locale packages).

The locale-definition form is provided by the (gnu system locale) module.  Details are given below.

 -- Data Type: locale-definition
     This is the data type of a locale definition.

     name
          The name of the locale.  See Locale Names (The GNU C Library Reference Manual), for more information on locale names.

     source
          The name of the source for that locale.  This is typically the LANGUAGE_TERRITORY part of the locale name.

     charset (default: "UTF-8")
          The ``character set'' or ``code set'' for that locale, as defined by IANA (http://www.iana.org/assignments/character-sets).

 -- Scheme Variable: %default-locale-definitions
     A list of commonly used UTF-8 locales, used as the default value of the locale-definitions field of operating-system declarations.

     These locale definitions use the normalized codeset for the part that follows the dot in the name (see normalized codeset (The GNU C Library Reference Manual)).  So for instance it has uk_UA.utf8 but not, say, uk_UA.UTF-8.

Locale Data Compatibility Considerations
........................................

operating-system declarations provide a locale-libcs field to specify the GNU libc packages that are used to compile locale declarations (see operating-system Reference).  ``Why would I care?'', you may ask.  Well, it turns out that the binary format of locale data is occasionally incompatible from one libc version to another.

For instance, a program linked against libc version 2.21 is unable to read locale data produced with libc 2.22; worse, that program aborts instead of simply ignoring the incompatible locale data (Versions 2.23 and later of GNU libc will simply skip the incompatible locale data, which is already an improvement.). Similarly, a program linked against libc 2.22 can read most, but not all, of the locale data from libc 2.21 (specifically, LC_COLLATE data is incompatible); thus calls to setlocale may fail, but programs will not abort.

The ``problem'' in GuixSD is that users have a lot of freedom: They can choose whether and when to upgrade software in their profiles, and might be using a libc version different from the one the system administrator used to build the system-wide locale data.

Fortunately, unprivileged users can also install their own locale data and define GUIX_LOCPATH accordingly (see GUIX_LOCPATH and locale packages).

Still, it is best if the system-wide locale data at /run/current-system/locale is built for all the libc versions actually in use on the system, so that all the programs can access it---this is especially crucial on a multi-user system.  To do that, the administrator can specify several libc packages in the locale-libcs field of operating-system:

     (use-package-modules base)

     (operating-system
       ;; ...
       (locale-libcs (list glibc-2.21 (canonical-package glibc))))

This example would lead to a system containing locale definitions for both libc 2.21 and the current version of libc in /run/current-system/locale.

Services
--------

An important part of preparing an operating-system declaration is listing system services and their configuration (see Using the Configuration System).  System services are typically daemons launched when the system boots, or other actions needed at that time---e.g., configuring network access.

GuixSD has a broad definition of ``service'' (see Service Composition), but many services are managed by the GNU Shepherd (see Shepherd Services).  On a running system, the herd command allows you to list the available services, show their status, start and stop them, or do other specific operations (see Jump Start (The GNU Shepherd Manual)).  For example:

     # herd status

The above command, run as root, lists the currently defined services.  The herd doc command shows a synopsis of the given service:

     # herd doc nscd
     Run libc's name service cache daemon (nscd).

The start, stop, and restart sub-commands have the effect you would expect.  For instance, the commands below stop the nscd service and restart the Xorg display server:

     # herd stop nscd
     Service nscd has been stopped.
     # herd restart xorg-server
     Service xorg-server has been stopped.
     Service xorg-server has been started.

The following sections document the available services, starting with the core services, that may be used in an operating-system declaration.

Base Services
.............

The (gnu services base) module provides definitions for the basic services that one expects from the system.  The services exported by this module are listed below.

 -- Scheme Variable: %base-services
     This variable contains a list of basic services (see Service Types and Services, for more information on service objects) one would expect from the system: a login service (mingetty) on each tty, syslogd, the libc name service cache daemon (nscd), the udev device manager, and more.

     This is the default value of the services field of operating-system declarations.  Usually, when customizing a system, you will want to append services to %BASE-SERVICES, like this:

          (cons* (avahi-service) (lsh-service) %base-services)

 -- Scheme Procedure: host-name-service NAME
     Return a service that sets the host name to NAME.

 -- Scheme Procedure: login-service CONFIG
     Return a service to run login according to CONFIG, a <login-configuration> object, which specifies the message of the day, among other things.

 -- Data Type: login-configuration
     This is the data type representing the configuration of login.

     motd
          A file-like object containing the ``message of the day''.

     allow-empty-passwords? (default: #t)
          Allow empty passwords by default so that first-time users can log in when the 'root' account has just been created.

 -- Scheme Procedure: mingetty-service CONFIG
     Return a service to run mingetty according to CONFIG, a <mingetty-configuration> object, which specifies the tty to run, among other things.

 -- Data Type: mingetty-configuration
     This is the data type representing the configuration of Mingetty, which implements console log-in.

     tty
          The name of the console this Mingetty runs on---e.g., "tty1".

     auto-login (default: #f)
          When true, this field must be a string denoting the user name under which the system automatically logs in.  When it is #f, a user name and password must be entered to log in.

     login-program (default: #f)
          This must be either #f, in which case the default log-in program is used (login from the Shadow tool suite), or a gexp denoting the name of the log-in program.

     login-pause? (default: #f)
          When set to #t in conjunction with AUTO-LOGIN, the user will have to press a key before the log-in shell is launched.

     mingetty (default: MINGETTY)
          The Mingetty package to use.

 -- Scheme Procedure: kmscon-service-type CONFIG
     Return a service to run kmscon (https://www.freedesktop.org/wiki/Software/kmscon) according to CONFIG, a <kmscon-configuration> object, which specifies the tty to run, among other things.

 -- Data Type: kmscon-configuration
     This is the data type representing the configuration of Kmscon, which implements console log-in.

     virtual-terminal
          The name of the console this Kmscon runs on---e.g., "tty1".

     login-program (default: #~(string-append #$shadow "/bin/login"))
          A gexp denoting the name of the log-in program. The default log-in program is login from the Shadow tool suite.

     login-arguments (default: '("-p"))
          A list of arguments to pass to login.

     hardware-acceleration? (default: #f)
          Whether to use hardware acceleration.

     kmscon (default: KMSCON)
          The Kmscon package to use.

 -- Scheme Procedure: nscd-service [CONFIG] [#:glibc glibc]
     [#:name-services '()]
     Return a service that runs the libc name service cache daemon (nscd) with the given CONFIG---an <nscd-configuration> object.  See Name Service Switch, for an example.

 -- Scheme Variable: %nscd-default-configuration
     This is the default <nscd-configuration> value (see below) used by nscd-service.  It uses the caches defined by %NSCD-DEFAULT-CACHES; see below.

 -- Data Type: nscd-configuration
     This is the data type representing the name service cache daemon (nscd) configuration.

     name-services (default: '())
          List of packages denoting name services that must be visible to the nscd---e.g., (list NSS-MDNS).

     glibc (default: GLIBC)
          Package object denoting the GNU C Library providing the nscd command.

     log-file (default: "/var/log/nscd.log")
          Name of the nscd log file.  This is where debugging output goes when debug-level is strictly positive.

     debug-level (default: 0)
          Integer denoting the debugging levels.  Higher numbers mean that more debugging output is logged.

     caches (default: %NSCD-DEFAULT-CACHES)
          List of <nscd-cache> objects denoting things to be cached; see below.

 -- Data Type: nscd-cache
     Data type representing a cache database of nscd and its parameters.

     database
          This is a symbol representing the name of the database to be cached. Valid values are passwd, group, hosts, and services, which designate the corresponding NSS database (see NSS Basics (The GNU C Library Reference Manual)).

     positive-time-to-live
     negative-time-to-live (default: 20)
          A number representing the number of seconds during which a positive or negative lookup result remains in cache.

     check-files? (default: #t)
          Whether to check for updates of the files corresponding to DATABASE.

          For instance, when DATABASE is hosts, setting this flag instructs nscd to check for updates in /etc/hosts and to take them into account.

     persistent? (default: #t)
          Whether the cache should be stored persistently on disk.

     shared? (default: #t)
          Whether the cache should be shared among users.

     max-database-size (default: 32 MiB)
          Maximum size in bytes of the database cache.

 -- Scheme Variable: %nscd-default-caches
     List of <nscd-cache> objects used by default by nscd-configuration (see above).

     It enables persistent and aggressive caching of service and host name lookups.  The latter provides better host name lookup performance, resilience in the face of unreliable name servers, and also better privacy---often the result of host name lookups is in local cache, so external name servers do not even need to be queried.

 -- Data Type: syslog-configuration
     This data type represents the configuration of the syslog daemon.

     syslogd (default: #~(string-append #$inetutils "/libexec/syslogd"))
          The syslog daemon to use.

     config-file (default: %default-syslog.conf)
          The syslog configuration file to use.

 -- Scheme Procedure: syslog-service CONFIG
     Return a service that runs a syslog daemon according to CONFIG.

     See syslogd invocation (GNU Inetutils), for more information on the configuration file syntax.

 -- Data Type: guix-configuration
     This data type represents the configuration of the Guix build daemon. See Invoking guix-daemon, for more information.

     guix (default: GUIX)
          The Guix package to use.

     build-group (default: "guixbuild")
          Name of the group for build user accounts.

     build-accounts (default: 10)
          Number of build user accounts to create.

     authorize-key? (default: #t)
          Whether to authorize the substitute keys listed in authorized-keys---by default that of hydra.gnu.org (see Substitutes).

     authorized-keys (default: %DEFAULT-AUTHORIZED-GUIX-KEYS)
          The list of authorized key files for archive imports, as a list of string-valued gexps (see Invoking guix archive).  By default, it contains that of hydra.gnu.org (see Substitutes).

     use-substitutes? (default: #t)
          Whether to use substitutes.

     substitute-urls (default: %DEFAULT-SUBSTITUTE-URLS)
          The list of URLs where to look for substitutes by default.

     extra-options (default: '())
          List of extra command-line options for guix-daemon.

     lsof (default: LSOF)
     lsh (default: LSH)
          The lsof and lsh packages to use.

 -- Scheme Procedure: guix-service CONFIG
     Return a service that runs the Guix build daemon according to CONFIG.

 -- Scheme Procedure: udev-service [#:udev udev]
     Run UDEV, which populates the /dev directory dynamically.

 -- Scheme Procedure: urandom-seed-service #F
     Save some entropy in %RANDOM-SEED-FILE to seed /dev/urandom when rebooting.

 -- Scheme Variable: %random-seed-file
     This is the name of the file where some random bytes are saved by URANDOM-SEED-SERVICE to seed /dev/urandom when rebooting. It defaults to /var/lib/random-seed.

 -- Scheme Procedure: console-keymap-service FILES ...
     Return a service to load console keymaps from FILES using loadkeys command.  Most likely, you want to load some default keymap, which can be done like this:

          (console-keymap-service "dvorak")

     Or, for example, for a Swedish keyboard, you may need to combine the following keymaps:

          (console-keymap-service "se-lat6" "se-fi-lat6")

     Also you can specify a full file name (or file names) of your keymap(s). See man loadkeys for details.

 -- Scheme Procedure: gpm-service [#:gpm GPM]
     [#:options]
     Run GPM, the general-purpose mouse daemon, with the given command-line OPTIONS.  GPM allows users to use the mouse in the console, notably to select, copy, and paste text.  The default value of OPTIONS uses the ps2 protocol, which works for both USB and PS/2 mice.

     This service is not part of %BASE-SERVICES.

 -- Scheme Procedure: guix-publish-service [#:guix GUIX]
     [#:port 80] [#:host "localhost"]
     Return a service that runs guix publish listening on HOST and PORT (see Invoking guix publish).

     This assumes that /etc/guix already contains a signing key pair as created by guix archive --generate-key (see Invoking guix archive).  If that is not the case, the service will fail to start.

 -- Scheme Procedure: rngd-service [#:rng-tools RNG-TOOLS]
     [#:device "/dev/hwrng"]
     Return a service that runs the rngd program from RNG-TOOLS to add DEVICE to the kernel's entropy pool.  The service will fail if DEVICE does not exist.

 -- Scheme Procedure: pam-limits-service [#:limits LIMITS]

     Return a service that installs a configuration file for the pam_limits module (http://linux-pam.org/Linux-PAM-html/sag-pam_limits.html).  The procedure optionally takes a list of pam-limits-entry values, which can be used to specify ulimit limits and nice priority limits to user sessions.

     The following limits definition sets two hard and soft limits for all login sessions of users in the realtime group:

          (pam-limits-service
           (list
            (pam-limits-entry "@realtime" 'both 'rtprio 99)
            (pam-limits-entry "@realtime" 'both 'memlock 'unlimited)))

     The first entry increases the maximum realtime priority for non-privileged processes; the second entry lifts any restriction of the maximum address space that can be locked in memory.  These settings are commonly used for real-time audio systems.

Scheduled Job Execution
.......................

The (gnu services mcron) module provides an interface to GNU mcron, a daemon to run jobs at scheduled times (see GNU mcron).  GNU mcron is similar to the traditional Unix cron daemon; the main difference is that it is implemented in Guile Scheme, which provides a lot of flexibility when specifying the scheduling of jobs and their actions.

The example below defines an operating system that runs the updatedb (see Invoking updatedb (Finding Files)) and the guix gc commands (see Invoking guix gc) daily, as well as the mkid command on behalf of an unprivileged user (see mkid invocation (ID Database Utilities)).  It uses gexps to introduce job definitions that are passed to mcron (see G-Expressions).

     (use-modules (guix) (gnu) (gnu services mcron))
     (use-package-modules base idutils)

     (define updatedb-job
       ;; Run 'updatedb' at 3AM every day.  Here we write the
       ;; job's action as a Scheme procedure.
       #~(job '(next-hour '(3))
              (lambda ()
                (execl (string-append #$findutils "/bin/updatedb")
                       "updatedb"
                       "--prunepaths=/tmp /var/tmp /gnu/store"))))

     (define garbage-collector-job
       ;; Collect garbage 5 minutes after midnight every day.
       ;; The job's action is a shell command.
       #~(job "5 0 * * *"            ;Vixie cron syntax
              "guix gc -F 1G"))

     (define idutils-job
       ;; Update the index database as user "charlie" at 12:15PM
       ;; and 19:15PM.  This runs from the user's home directory.
       #~(job '(next-minute-from (next-hour '(12 19)) '(15))
              (string-append #$idutils "/bin/mkid src")
              #:user "charlie"))

     (operating-system
       ;; ...
       (services (cons (mcron-service (list garbage-collector-job
                                            updatedb-job
                                            idutils-job))
                       %base-services)))

See mcron job specifications (GNU mcron), for more information on mcron job specifications.  Below is the reference of the mcron service.

 -- Scheme Procedure: mcron-service JOBS [#:mcron MCRON2]
     Return an mcron service running MCRON that schedules JOBS, a list of gexps denoting mcron job specifications.

     This is a shorthand for:

          (service mcron-service-type
                   (mcron-configuration (mcron mcron) (jobs jobs)))

 -- Scheme Variable: mcron-service-type
     This is the type of the mcron service, whose value is an mcron-configuration object.

     This service type can be the target of a service extension that provides it additional job specifications (see Service Composition).  In other words, it is possible to define services that provide additional mcron jobs to run.

 -- Data Type: mcron-configuration
     Data type representing the configuration of mcron.

     mcron (default: MCRON2)
          The mcron package to use.

     jobs
          This is a list of gexps (see G-Expressions), where each gexp corresponds to an mcron job specification (see mcron job specifications (GNU mcron)).

Log Rotation
............

Log files such as those found in /var/log tend to grow endlessly, so it's a good idea to rotate them once in a while---i.e., archive their contents in separate files, possibly compressed.  The (gnu services admin) module provides an interface to GNU Rot[t]log, a log rotation tool (see GNU Rot[t]log Manual).

The example below defines an operating system that provides log rotation with the default settings.

     (use-modules (guix) (gnu))
     (use-service-modules admin mcron)
     (use-package-modules base idutils)

     (operating-system
       ;; ...
       (services (cons* (mcron-service)
                        (service rottlog-service-type (rottlog-configuration))
                        %base-services)))

 -- Scheme Variable: rottlog-service-type
     This is the type of the Rottlog service, whose value is a rottlog-configuration object.

     This service type can define mcron jobs (see Scheduled Job Execution) to run the rottlog service.

 -- Data Type: rottlog-configuration
     Data type representing the configuration of rottlog.

     rottlog (default: rottlog)
          The Rottlog package to use.

     rc-file (default: (file-append rottlog "/etc/rc"))
          The Rottlog configuration file to use (see Mandatory RC Variables (GNU Rot[t]log Manual)).

     periodic-rotations (default: `(("weekly" %default-rotatations)))
          A list of Rottlog period-name/period-config tuples.

          For example, taking an example from the Rottlog manual (see Period Related File Examples (GNU Rot[t]log Manual)), a valid tuple might be:

               ("daily" ,(plain-file "daily"
                                     "\
                    /var/log/apache/* {
                       storedir apache-archives
                       rotate 6
                       notifempty
                       nocompress
                    }"))

     jobs
          This is a list of gexps where each gexp corresponds to an mcron job specification (see Scheduled Job Execution).

 -- Scheme Variable: %default-rotations
     Specifies weekly rotation of %ROTATED-FILES and "/var/log/shepherd.log".

 -- Scheme Variable: %rotated-files
     The list of syslog-controlled files to be rotated.  By default it is: '("/var/log/messages" "/var/log/secure").

Networking Services
...................

The (gnu services networking) module provides services to configure the network interface.

 -- Scheme Procedure: dhcp-client-service [#:dhcp ISC-DHCP]
     Return a service that runs DHCP, a Dynamic Host Configuration Protocol (DHCP) client, on all the non-loopback network interfaces.

 -- Scheme Procedure: static-networking-service INTERFACE IP
     [#:netmask #f] [#:gateway #f] [#:name-servers '()]
     Return a service that starts INTERFACE with address IP.  If NETMASK is true, use it as the network mask.  If GATEWAY is true, it must be a string specifying the default network gateway.

 -- Scheme Procedure: wicd-service [#:wicd WICD]
     Return a service that runs Wicd (https://launchpad.net/wicd), a network management daemon that aims to simplify wired and wireless networking.

     This service adds the WICD package to the global profile, providing several commands to interact with the daemon and configure networking: wicd-client, a graphical user interface, and the wicd-cli and wicd-curses user interfaces.

 -- Scheme Procedure: network-manager-service
     [#:network-manager NETWORK-MANAGER]
     Return a service that runs NetworkManager, a network connection manager attempting to keep network connectivity active when available.

 -- Scheme Procedure: connman-service
     [#:connman CONNMAN]
     Return a service that runs Connman (https://01.org/connman), a network connection manager.

     This service adds the CONNMAN package to the global profile, providing several the connmanctl command to interact with the daemon and configure networking."

 -- Scheme Variable: wpa-supplicant-service-type
     This is the service type to run WPA supplicant (https://w1.fi/wpa_supplicant/), an authentication daemon required to authenticate against encrypted WiFi or ethernet networks.  It is configured to listen for requests on D-Bus.

     The value of this service is the wpa-supplicant package to use. Thus, it can be instantiated like this:

          (use-modules (gnu services networking)
                       (gnu packages admin))

          (service wpa-supplicant-service-type wpa-supplicant)

 -- Scheme Procedure: ntp-service [#:ntp NTP]
     [#:servers %NTP-SERVERS]
     [#:allow-large-adjustment? #f]
     Return a service that runs the daemon from NTP, the Network Time Protocol package (http://www.ntp.org).  The daemon will keep the system clock synchronized with that of SERVERS. ALLOW-LARGE-ADJUSTMENT? determines whether ntpd is allowed to make an initial adjustment of more than 1,000 seconds.

 -- Scheme Variable: %ntp-servers
     List of host names used as the default NTP servers.

 -- Scheme Procedure: tor-service [CONFIG-FILE] [#:tor TOR]
     Return a service to run the Tor (https://torproject.org) anonymous networking daemon.

     The daemon runs as the tor unprivileged user.  It is passed CONFIG-FILE, a file-like object, with an additional User tor line and lines for hidden services added via tor-hidden-service.  Run man tor for information about the configuration file.

 -- Scheme Procedure: tor-hidden-service NAME MAPPING
     Define a new Tor hidden service called NAME and implementing MAPPING.  MAPPING is a list of port/host tuples, such as:

           '((22 "127.0.0.1:22")
             (80 "127.0.0.1:8080"))

     In this example, port 22 of the hidden service is mapped to local port 22, and port 80 is mapped to local port 8080.

     This creates a /var/lib/tor/hidden-services/NAME directory, where the hostname file contains the .onion host name for the hidden service.

     See the Tor project's documentation (https://www.torproject.org/docs/tor-hidden-service.html.en) for more information.

 -- Scheme Procedure: bitlbee-service [#:bitlbee bitlbee]
     [#:interface "127.0.0.1"] [#:port 6667]
     [#:extra-settings ""]
     Return a service that runs BitlBee (http://bitlbee.org), a daemon that acts as a gateway between IRC and chat networks.

     The daemon will listen to the interface corresponding to the IP address specified in INTERFACE, on PORT.  127.0.0.1 means that only local clients can connect, whereas 0.0.0.0 means that connections can come from any networking interface.

     In addition, EXTRA-SETTINGS specifies a string to append to the configuration file.

Furthermore, (gnu services ssh) provides the following services.

 -- Scheme Procedure: lsh-service [#:host-key "/etc/lsh/host-key"]
     [#:daemonic? #t] [#:interfaces '()] [#:port-number 22]
     [#:allow-empty-passwords? #f] [#:root-login? #f]
     [#:syslog-output? #t] [#:x11-forwarding? #t]
     [#:tcp/ip-forwarding? #t] [#:password-authentication? #t]
     [#:public-key-authentication? #t] [#:initialize? #t]
     Run the lshd program from LSH to listen on port PORT-NUMBER. HOST-KEY must designate a file containing the host key, and readable only by root.

     When DAEMONIC? is true, lshd will detach from the controlling terminal and log its output to syslogd, unless one sets SYSLOG-OUTPUT? to false.  Obviously, it also makes lsh-service depend on existence of syslogd service.  When PID-FILE? is true, lshd writes its PID to the file called PID-FILE.

     When INITIALIZE? is true, automatically create the seed and host key upon service activation if they do not exist yet.  This may take long and require interaction.

     When INITIALIZE? is false, it is up to the user to initialize the randomness generator (see lsh-make-seed (LSH Manual)), and to create a key pair with the private key stored in file HOST-KEY (see lshd basics (LSH Manual)).

     When INTERFACES is empty, lshd listens for connections on all the network interfaces; otherwise, INTERFACES must be a list of host names or addresses.

     ALLOW-EMPTY-PASSWORDS? specifies whether to accept log-ins with empty passwords, and ROOT-LOGIN? specifies whether to accept log-ins as root.

     The other options should be self-descriptive.

 -- Scheme Variable: openssh-service-type
     This is the type for the OpenSSH (http://www.openssh.org) secure shell daemon, sshd.  Its value must be an openssh-configuration record as in this example:

          (service openssh-service-type
                   (openssh-configuration
                     (x11-forwarding? #t)
                     (permit-root-login 'without-password)))

     See below for details about openssh-configuration.

 -- Data Type: openssh-configuration
     This is the configuration record for OpenSSH's sshd.

     pid-file (default: "/var/run/sshd.pid")
          Name of the file where sshd writes its PID.

     port-number (default: 22)
          TCP port on which sshd listens for incoming connections.

     permit-root-login (default: #f)
          This field determines whether and when to allow logins as root.  If #f, root logins are disallowed; if #t, they are allowed. If it's the symbol 'without-password, then root logins are permitted but not with password-based authentication.

     allow-empty-passwords? (default: #f)
          When true, users with empty passwords may log in.  When false, they may not.

     password-authentication? (default: #t)
          When true, users may log in with their password.  When false, they have other authentication methods.

     public-key-authentication? (default: #t)
          When true, users may log in using public key authentication.  When false, users have to use other authentication method.

          Authorized public keys are stored in ~/.ssh/authorized_keys. This is used only by protocol version 2.

     rsa-authentication? (default: #t)
          When true, users may log in using pure RSA authentication.  When false, users have to use other means of authentication.  This is used only by protocol 1.

     x11-forwarding? (default: #f)
          When true, forwarding of X11 graphical client connections is enabled---in other words, ssh options -X and -Y will work.

     protocol-number (default: 2)
          The SSH protocol number to use.

 -- Scheme Procedure: dropbear-service [CONFIG]
     Run the Dropbear SSH daemon (https://matt.ucc.asn.au/dropbear/dropbear.html) with the given CONFIG, a <dropbear-configuration> object.

     For example, to specify a Dropbear service listening on port 1234, add this call to the operating system's services field:

          (dropbear-service (dropbear-configuration
                              (port-number 1234)))

 -- Data Type: dropbear-configuration
     This data type represents the configuration of a Dropbear SSH daemon.

     dropbear (default: DROPBEAR)
          The Dropbear package to use.

     port-number (default: 22)
          The TCP port where the daemon waits for incoming connections.

     syslog-output? (default: #t)
          Whether to enable syslog output.

     pid-file (default: "/var/run/dropbear.pid")
          File name of the daemon's PID file.

     root-login? (default: #f)
          Whether to allow root logins.

     allow-empty-passwords? (default: #f)
          Whether to allow empty passwords.

     password-authentication? (default: #t)
          Whether to enable password-based authentication.

 -- Scheme Variable: %facebook-host-aliases
     This variable contains a string for use in /etc/hosts (see Host Names (The GNU C Library Reference Manual)).  Each line contains a entry that maps a known server name of the Facebook on-line service---e.g., www.facebook.com---to the local host---127.0.0.1 or its IPv6 equivalent, ::1.

     This variable is typically used in the hosts-file field of an operating-system declaration (see /etc/hosts):

          (use-modules (gnu) (guix))

          (operating-system
            (host-name "mymachine")
            ;; ...
            (hosts-file
              ;; Create a /etc/hosts file with aliases for "localhost"
              ;; and "mymachine", as well as for Facebook servers.
              (plain-file "hosts"
                          (string-append (local-host-aliases host-name)
                                         %facebook-host-aliases))))

     This mechanism can prevent programs running locally, such as Web browsers, from accessing Facebook.

The (gnu services avahi) provides the following definition.

 -- Scheme Procedure: avahi-service [#:avahi AVAHI]
     [#:host-name #f] [#:publish? #t] [#:ipv4? #t]
     [#:ipv6? #t] [#:wide-area? #f]
     [#:domains-to-browse '()] [#:debug? #f]
     Return a service that runs avahi-daemon, a system-wide mDNS/DNS-SD responder that allows for service discovery and "zero-configuration" host name lookups (see http://avahi.org/), and extends the name service cache daemon (nscd) so that it can resolve .local host names using nss-mdns (http://0pointer.de/lennart/projects/nss-mdns/).  Additionally, add the AVAHI package to the system profile so that commands such as avahi-browse are directly usable.

     If HOST-NAME is different from #f, use that as the host name to publish for this machine; otherwise, use the machine's actual host name.

     When PUBLISH? is true, publishing of host names and services is allowed; in particular, avahi-daemon will publish the machine's host name and IP address via mDNS on the local network.

     When WIDE-AREA? is true, DNS-SD over unicast DNS is enabled.

     Boolean values IPV4? and IPV6? determine whether to use IPv4/IPv6 sockets.

X Window
........

Support for the X Window graphical display system---specifically Xorg---is provided by the (gnu services xorg) module.  Note that there is no xorg-service procedure.  Instead, the X server is started by the login manager, currently SLiM.

 -- Data Type: sddm-configuration
     This is the data type representing the sddm service configuration.

     display-server (default: "x11")
          Select display server to use for the greeter. Valid values are "x11" or "wayland".

     numlock (default: "on")
          Valid values are "on", "off" or "none".

     halt-command (default #~(string-apppend #$shepherd "/sbin/halt"))
          Command to run when halting.

     reboot-command (default #~(string-append #$shepherd "/sbin/reboot"))
          Command to run when rebooting.

     theme (default "maldives")
          Theme to use. Default themes provided by SDDM are "elarun" or "maldives".

     themes-directory (default "/run/current-system/profile/share/sddm/themes")
          Directory to look for themes.

     faces-directory (default "/run/current-system/profile/share/sddm/faces")
          Directory to look for faces.

     default-path (default "/run/current-system/profile/bin")
          Default PATH to use.

     minimum-uid (default 1000)
          Minimum UID to display in SDDM.

     maximum-uid (default 2000)
          Maximum UID to display in SDDM

     remember-last-user? (default #t)
          Remember last user.

     remember-last-session? (default #t)
          Remember last session.

     hide-users (default "")
          Usernames to hide from SDDM greeter.

     hide-shells (default #~(string-append #$shadow "/sbin/nologin"))
          Users with shells listed will be hidden from the SDDM greeter.

     session-command (default #~(string-append #$sddm "/share/sddm/scripts/wayland-session"))
          Script to run before starting a wayland session.

     sessions-directory (default "/run/current-system/profile/share/wayland-sessions")
          Directory to look for desktop files starting wayland sessions.

     xorg-server-path (default xorg-start-command)
          Path to xorg-server.

     xauth-path (default #~(string-append #$xauth "/bin/xauth"))
          Path to xauth.

     xephyr-path (default #~(string-append #$xorg-server "/bin/Xephyr"))
          Path to Xephyr.

     xdisplay-start (default #~(string-append #$sddm "/share/sddm/scripts/Xsetup"))
          Script to run after starting xorg-server.

     xdisplay-stop (default #~(string-append #$sddm "/share/sddm/scripts/Xstop"))
          Script to run before stopping xorg-server.

     xsession-command (default: xinitr )
          Script to run before starting a X session.

     xsessions-directory (default: "/run/current-system/profile/share/xsessions")
          Directory to look for desktop files starting X sessions.

     minimum-vt (default: 7)
          Minimum VT to use.

     xserver-arguments (default "-nolisten tcp")
          Arguments to pass to xorg-server.

     auto-login-user (default "")
          User to use for auto-login.

     auto-login-session (default "")
          Desktop file to use for auto-login.

     relogin? (default #f)
          Relogin after logout.

 -- Scheme Procedure: sddm-service config
     Return a service that spawns the SDDM graphical login manager for config of type <sddm-configuration>.

            (sddm-service (sddm-configuration
                           (auto-login-user "Alice")
                           (auto-login-session "xfce.desktop")))

 -- Scheme Procedure: slim-service [#:allow-empty-passwords? #f]
     [#:auto-login? #f] [#:default-user ""] [#:startx]
     [#:theme %DEFAULT-SLIM-THEME]
     [#:theme-name %DEFAULT-SLIM-THEME-NAME]
     Return a service that spawns the SLiM graphical login manager, which in turn starts the X display server with STARTX, a command as returned by xorg-start-command.

     SLiM automatically looks for session types described by the .desktop files in /run/current-system/profile/share/xsessions and allows users to choose a session from the log-in screen using F1.  Packages such as XFCE, SAWFISH, and RATPOISON provide .desktop files; adding them to the system-wide set of packages automatically makes them available at the log-in screen.

     In addition, ~/.xsession files are honored.  When available, ~/.xsession must be an executable that starts a window manager and/or other X clients.

     When ALLOW-EMPTY-PASSWORDS? is true, allow logins with an empty password.  When AUTO-LOGIN? is true, log in automatically as DEFAULT-USER.

     If THEME is #f, use the default log-in theme; otherwise THEME must be a gexp denoting the name of a directory containing the theme to use.  In that case, THEME-NAME specifies the name of the theme.

 -- Scheme Variable: %default-theme
 -- Scheme Variable: %default-theme-name
     The G-Expression denoting the default SLiM theme and its name.

 -- Scheme Procedure: xorg-start-command [#:guile]
     [#:configuration-file #f] [#:xorg-server XORG-SERVER]
     Return a derivation that builds a GUILE script to start the X server from XORG-SERVER.  CONFIGURATION-FILE is the server configuration file or a derivation that builds it; when omitted, the result of xorg-configuration-file is used.

     Usually the X server is started by a login manager.

 -- Scheme Procedure: xorg-configuration-file
     [#:drivers '()] [#:resolutions '()] [#:extra-config '()]
     Return a configuration file for the Xorg server containing search paths for all the common drivers.

     DRIVERS must be either the empty list, in which case Xorg chooses a graphics driver automatically, or a list of driver names that will be tried in this order---e.g., (\"modesetting\" \"vesa\").

     Likewise, when RESOLUTIONS is the empty list, Xorg chooses an appropriate screen resolution; otherwise, it must be a list of resolutions---e.g., ((1024 768) (640 480)).

     Last, EXTRA-CONFIG is a list of strings or objects appended to the text-file* argument list.  It is used to pass extra text to be added verbatim to the configuration file.

 -- Scheme Procedure: screen-locker-service PACKAGE [NAME]
     Add PACKAGE, a package for a screen-locker or screen-saver whose command is PROGRAM, to the set of setuid programs and add a PAM entry for it.  For example:

          (screen-locker-service xlockmore "xlock")

     makes the good ol' XlockMore usable.

Printing Services
.................

The (gnu services cups) module provides a Guix service definition for the CUPS printing service.  To add printer support to a GuixSD system, add a cups-service to the operating system definition:

 -- Scheme Variable: cups-service-type
     The service type for the CUPS print server.  Its value should be a valid CUPS configuration (see below).  For example:

          (service cups-service-type (cups-configuration))

The CUPS configuration controls the basic things about your CUPS installation: what interfaces it listens on, what to do if a print job fails, how much logging to do, and so on.  To actually add a printer, you have to visit the http://localhost:631 URL, or use a tool such as GNOME's printer configuration services.  By default, configuring a CUPS service will generate a self-signed certificate if needed, for secure connections to the print server.

One way you might want to customize CUPS is to enable or disable the web interface.  You can do that directly, like this:

     (service cups-service-type
              (cups-configuration
                (web-interface? #f)))

The available configuration parameters follow.  Each parameter definition is preceded by its type; for example, string-list foo indicates that the foo parameter should be specified as a list of strings.  There is also a way to specify the configuration as a string, if you have an old cupsd.conf file that you want to port over from some other system; see the end for more details.

Available cups-configuration fields are:

 -- cups-configuration parameter: package cups
     The CUPS package.

 -- cups-configuration parameter: package-list extensions
     Drivers and other extensions to the CUPS package.

 -- cups-configuration parameter: files-configuration files-configuration
     Configuration of where to write logs, what directories to use for print spools, and related privileged configuration parameters.

     Available files-configuration fields are:

      -- files-configuration parameter: log-location access-log
          Defines the access log filename.  Specifying a blank filename disables access log generation.  The value stderr causes log entries to be sent to the standard error file when the scheduler is running in the foreground, or to the system log daemon when run in the background.  The value syslog causes log entries to be sent to the system log daemon.  The server name may be included in filenames using the string %s, as in /var/log/cups/%s-access_log.

          Defaults to "/var/log/cups/access_log".

      -- files-configuration parameter: file-name cache-dir
          Where CUPS should cache data.

          Defaults to "/var/cache/cups".

      -- files-configuration parameter: string config-file-perm
          Specifies the permissions for all configuration files that the scheduler writes.

          Note that the permissions for the printers.conf file are currently masked to only allow access from the scheduler user (typically root). This is done because printer device URIs sometimes contain sensitive authentication information that should not be generally known on the system.  There is no way to disable this security feature.

          Defaults to "0640".

      -- files-configuration parameter: log-location error-log
          Defines the error log filename.  Specifying a blank filename disables access log generation.  The value stderr causes log entries to be sent to the standard error file when the scheduler is running in the foreground, or to the system log daemon when run in the background.  The value syslog causes log entries to be sent to the system log daemon.  The server name may be included in filenames using the string %s, as in /var/log/cups/%s-error_log.

          Defaults to "/var/log/cups/error_log".

      -- files-configuration parameter: string fatal-errors
          Specifies which errors are fatal, causing the scheduler to exit.  The kind strings are:

          none
               No errors are fatal.

          all
               All of the errors below are fatal.

          browse
               Browsing initialization errors are fatal, for example failed connections to the DNS-SD daemon.

          config
               Configuration file syntax errors are fatal.

          listen
               Listen or Port errors are fatal, except for IPv6 failures on the loopback or any addresses.

          log
               Log file creation or write errors are fatal.

          permissions
               Bad startup file permissions are fatal, for example shared TLS certificate and key files with world-read permissions.

          Defaults to "all -browse".

      -- files-configuration parameter: boolean file-device?
          Specifies whether the file pseudo-device can be used for new printer queues.  The URI file:///dev/null is always allowed.

          Defaults to #f.

      -- files-configuration parameter: string group
          Specifies the group name or ID that will be used when executing external programs.

          Defaults to "lp".

      -- files-configuration parameter: string log-file-perm
          Specifies the permissions for all log files that the scheduler writes.

          Defaults to "0644".

      -- files-configuration parameter: log-location page-log
          Defines the page log filename.  Specifying a blank filename disables access log generation.  The value stderr causes log entries to be sent to the standard error file when the scheduler is running in the foreground, or to the system log daemon when run in the background.  The value syslog causes log entries to be sent to the system log daemon.  The server name may be included in filenames using the string %s, as in /var/log/cups/%s-page_log.

          Defaults to "/var/log/cups/page_log".

      -- files-configuration parameter: string remote-root
          Specifies the username that is associated with unauthenticated accesses by clients claiming to be the root user.  The default is remroot.

          Defaults to "remroot".

      -- files-configuration parameter: file-name request-root
          Specifies the directory that contains print jobs and other HTTP request data.

          Defaults to "/var/spool/cups".

      -- files-configuration parameter: sandboxing sandboxing
          Specifies the level of security sandboxing that is applied to print filters, backends, and other child processes of the scheduler; either relaxed or strict.  This directive is currently only used/supported on macOS.

          Defaults to strict.

      -- files-configuration parameter: file-name server-keychain
          Specifies the location of TLS certificates and private keys.  CUPS will look for public and private keys in this directory: a .crt files for PEM-encoded certificates and corresponding .key files for PEM-encoded private keys.

          Defaults to "/etc/cups/ssl".

      -- files-configuration parameter: file-name server-root
          Specifies the directory containing the server configuration files.

          Defaults to "/etc/cups".

      -- files-configuration parameter: boolean sync-on-close?
          Specifies whether the scheduler calls fsync(2) after writing configuration or state files.

          Defaults to #f.

      -- files-configuration parameter: space-separated-string-list system-group
          Specifies the group(s) to use for @SYSTEM group authentication.

      -- files-configuration parameter: file-name temp-dir
          Specifies the directory where temporary files are stored.

          Defaults to "/var/spool/cups/tmp".

      -- files-configuration parameter: string user
          Specifies the user name or ID that is used when running external programs.

          Defaults to "lp".

 -- cups-configuration parameter: access-log-level access-log-level
     Specifies the logging level for the AccessLog file.  The config level logs when printers and classes are added, deleted, or modified and when configuration files are accessed or updated.  The actions level logs when print jobs are submitted, held, released, modified, or canceled, and any of the conditions for config.  The all level logs all requests.

     Defaults to actions.

 -- cups-configuration parameter: boolean auto-purge-jobs?
     Specifies whether to purge job history data automatically when it is no longer required for quotas.

     Defaults to #f.

 -- cups-configuration parameter: browse-local-protocols browse-local-protocols
     Specifies which protocols to use for local printer sharing.

     Defaults to dnssd.

 -- cups-configuration parameter: boolean browse-web-if?
     Specifies whether the CUPS web interface is advertised.

     Defaults to #f.

 -- cups-configuration parameter: boolean browsing?
     Specifies whether shared printers are advertised.

     Defaults to #f.

 -- cups-configuration parameter: string classification
     Specifies the security classification of the server.  Any valid banner name can be used, including "classified", "confidential", "secret", "topsecret", and "unclassified", or the banner can be omitted to disable secure printing functions.

     Defaults to "".

 -- cups-configuration parameter: boolean classify-override?
     Specifies whether users may override the classification (cover page) of individual print jobs using the job-sheets option.

     Defaults to #f.

 -- cups-configuration parameter: default-auth-type default-auth-type
     Specifies the default type of authentication to use.

     Defaults to Basic.

 -- cups-configuration parameter: default-encryption default-encryption
     Specifies whether encryption will be used for authenticated requests.

     Defaults to Required.

 -- cups-configuration parameter: string default-language
     Specifies the default language to use for text and web content.

     Defaults to "en".

 -- cups-configuration parameter: string default-paper-size
     Specifies the default paper size for new print queues.  "Auto" uses a locale-specific default, while "None" specifies there is no default paper size.  Specific size names are typically "Letter" or "A4".

     Defaults to "Auto".

 -- cups-configuration parameter: string default-policy
     Specifies the default access policy to use.

     Defaults to "default".

 -- cups-configuration parameter: boolean default-shared?
     Specifies whether local printers are shared by default.

     Defaults to #t.

 -- cups-configuration parameter: non-negative-integer dirty-clean-interval
     Specifies the delay for updating of configuration and state files, in seconds.  A value of 0 causes the update to happen as soon as possible, typically within a few milliseconds.

     Defaults to 30.

 -- cups-configuration parameter: error-policy error-policy
     Specifies what to do when an error occurs.  Possible values are abort-job, which will discard the failed print job; retry-job, which will retry the job at a later time; retry-this-job, which retries the failed job immediately; and stop-printer, which stops the printer.

     Defaults to stop-printer.

 -- cups-configuration parameter: non-negative-integer filter-limit
     Specifies the maximum cost of filters that are run concurrently, which can be used to minimize disk, memory, and CPU resource problems.  A limit of 0 disables filter limiting.  An average print to a non-PostScript printer needs a filter limit of about 200.  A PostScript printer needs about half that (100).  Setting the limit below these thresholds will effectively limit the scheduler to printing a single job at any time.

     Defaults to 0.

 -- cups-configuration parameter: non-negative-integer filter-nice
     Specifies the scheduling priority of filters that are run to print a job.  The nice value ranges from 0, the highest priority, to 19, the lowest priority.

     Defaults to 0.

 -- cups-configuration parameter: host-name-lookups host-name-lookups
     Specifies whether to do reverse lookups on connecting clients.  The double setting causes cupsd to verify that the hostname resolved from the address matches one of the addresses returned for that hostname.  Double lookups also prevent clients with unregistered addresses from connecting to your server.  Only set this option to #t or double if absolutely required.

     Defaults to #f.

 -- cups-configuration parameter: non-negative-integer job-kill-delay
     Specifies the number of seconds to wait before killing the filters and backend associated with a canceled or held job.

     Defaults to 30.

 -- cups-configuration parameter: non-negative-integer job-retry-interval
     Specifies the interval between retries of jobs in seconds.  This is typically used for fax queues but can also be used with normal print queues whose error policy is retry-job or retry-current-job.

     Defaults to 30.

 -- cups-configuration parameter: non-negative-integer job-retry-limit
     Specifies the number of retries that are done for jobs.  This is typically used for fax queues but can also be used with normal print queues whose error policy is retry-job or retry-current-job.

     Defaults to 5.

 -- cups-configuration parameter: boolean keep-alive?
     Specifies whether to support HTTP keep-alive connections.

     Defaults to #t.

 -- cups-configuration parameter: non-negative-integer keep-alive-timeout
     Specifies how long an idle client connection remains open, in seconds.

     Defaults to 30.

 -- cups-configuration parameter: non-negative-integer limit-request-body
     Specifies the maximum size of print files, IPP requests, and HTML form data.  A limit of 0 disables the limit check.

     Defaults to 0.

 -- cups-configuration parameter: multiline-string-list listen
     Listens on the specified interfaces for connections.  Valid values are of the form ADDRESS:PORT, where ADDRESS is either an IPv6 address enclosed in brackets, an IPv4 address, or * to indicate all addresses.  Values can also be file names of local UNIX domain sockets.  The Listen directive is similar to the Port directive but allows you to restrict access to specific interfaces or networks.

 -- cups-configuration parameter: non-negative-integer listen-back-log
     Specifies the number of pending connections that will be allowed.  This normally only affects very busy servers that have reached the MaxClients limit, but can also be triggered by large numbers of simultaneous connections.  When the limit is reached, the operating system will refuse additional connections until the scheduler can accept the pending ones.

     Defaults to 128.

 -- cups-configuration parameter: location-access-control-list location-access-controls
     Specifies a set of additional access controls.

     Available location-access-controls fields are:

      -- location-access-controls parameter: file-name path
          Specifies the URI path to which the access control applies.

      -- location-access-controls parameter: access-control-list access-controls
          Access controls for all access to this path, in the same format as the access-controls of operation-access-control.

          Defaults to ().

      -- location-access-controls parameter: method-access-control-list method-access-controls
          Access controls for method-specific access to this path.

          Defaults to ().

          Available method-access-controls fields are:

           -- method-access-controls parameter: boolean reverse?
               If #t, apply access controls to all methods except the listed methods.  Otherwise apply to only the listed methods.

               Defaults to #f.

           -- method-access-controls parameter: method-list methods
               Methods to which this access control applies.

               Defaults to ().

           -- method-access-controls parameter: access-control-list access-controls
               Access control directives, as a list of strings.  Each string should be one directive, such as "Order allow,deny".

               Defaults to ().

 -- cups-configuration parameter: non-negative-integer log-debug-history
     Specifies the number of debugging messages that are retained for logging if an error occurs in a print job.  Debug messages are logged regardless of the LogLevel setting.

     Defaults to 100.

 -- cups-configuration parameter: log-level log-level
     Specifies the level of logging for the ErrorLog file.  The value none stops all logging while debug2 logs everything.

     Defaults to info.

 -- cups-configuration parameter: log-time-format log-time-format
     Specifies the format of the date and time in the log files.  The value standard logs whole seconds while usecs logs microseconds.

     Defaults to standard.

 -- cups-configuration parameter: non-negative-integer max-clients
     Specifies the maximum number of simultaneous clients that are allowed by the scheduler.

     Defaults to 100.

 -- cups-configuration parameter: non-negative-integer max-clients-per-host
     Specifies the maximum number of simultaneous clients that are allowed from a single address.

     Defaults to 100.

 -- cups-configuration parameter: non-negative-integer max-copies
     Specifies the maximum number of copies that a user can print of each job.

     Defaults to 9999.

 -- cups-configuration parameter: non-negative-integer max-hold-time
     Specifies the maximum time a job may remain in the indefinite hold state before it is canceled.  A value of 0 disables cancellation of held jobs.

     Defaults to 0.

 -- cups-configuration parameter: non-negative-integer max-jobs
     Specifies the maximum number of simultaneous jobs that are allowed.  Set to 0 to allow an unlimited number of jobs.

     Defaults to 500.

 -- cups-configuration parameter: non-negative-integer max-jobs-per-printer
     Specifies the maximum number of simultaneous jobs that are allowed per printer.  A value of 0 allows up to MaxJobs jobs per printer.

     Defaults to 0.

 -- cups-configuration parameter: non-negative-integer max-jobs-per-user
     Specifies the maximum number of simultaneous jobs that are allowed per user.  A value of 0 allows up to MaxJobs jobs per user.

     Defaults to 0.

 -- cups-configuration parameter: non-negative-integer max-job-time
     Specifies the maximum time a job may take to print before it is canceled, in seconds.  Set to 0 to disable cancellation of "stuck" jobs.

     Defaults to 10800.

 -- cups-configuration parameter: non-negative-integer max-log-size
     Specifies the maximum size of the log files before they are rotated, in bytes.  The value 0 disables log rotation.

     Defaults to 1048576.

 -- cups-configuration parameter: non-negative-integer multiple-operation-timeout
     Specifies the maximum amount of time to allow between files in a multiple file print job, in seconds.

     Defaults to 300.

 -- cups-configuration parameter: string page-log-format
     Specifies the format of PageLog lines.  Sequences beginning with percent (%) characters are replaced with the corresponding information, while all other characters are copied literally.  The following percent sequences are recognized:

     %%
          insert a single percent character

     %{name}
          insert the value of the specified IPP attribute

     %C
          insert the number of copies for the current page

     %P
          insert the current page number

     %T
          insert the current date and time in common log format

     %j
          insert the job ID

     %p
          insert the printer name

     %u
          insert the username

     A value of the empty string disables page logging.  The string %p %u %j %T %P %C %{job-billing} %{job-originating-host-name} %{job-name} %{media} %{sides} creates a page log with the standard items.

     Defaults to "".

 -- cups-configuration parameter: environment-variables environment-variables
     Passes the specified environment variable(s) to child processes; a list of strings.

     Defaults to ().

 -- cups-configuration parameter: policy-configuration-list policies
     Specifies named access control policies.

     Available policy-configuration fields are:

      -- policy-configuration parameter: string name
          Name of the policy.

      -- policy-configuration parameter: string job-private-access
          Specifies an access list for a job's private values.  @ACL maps to the printer's requesting-user-name-allowed or requesting-user-name-denied values.  @OWNER maps to the job's owner.  @SYSTEM maps to the groups listed for the system-group field of the files-config configuration, which is reified into the cups-files.conf(5) file.  Other possible elements of the access list include specific user names, and @GROUP to indicate members of a specific group.  The access list may also be simply all or default.

          Defaults to "@OWNER @SYSTEM".

      -- policy-configuration parameter: string job-private-values
          Specifies the list of job values to make private, or all, default, or none.

          Defaults to "job-name job-originating-host-name job-originating-user-name phone".

      -- policy-configuration parameter: string subscription-private-access
          Specifies an access list for a subscription's private values. @ACL maps to the printer's requesting-user-name-allowed or requesting-user-name-denied values.  @OWNER maps to the job's owner.  @SYSTEM maps to the groups listed for the system-group field of the files-config configuration, which is reified into the cups-files.conf(5) file.  Other possible elements of the access list include specific user names, and @GROUP to indicate members of a specific group.  The access list may also be simply all or default.

          Defaults to "@OWNER @SYSTEM".

      -- policy-configuration parameter: string subscription-private-values
          Specifies the list of job values to make private, or all, default, or none.

          Defaults to "notify-events notify-pull-method notify-recipient-uri notify-subscriber-user-name notify-user-data".

      -- policy-configuration parameter: operation-access-control-list access-controls
          Access control by IPP operation.

          Defaults to ().

 -- cups-configuration parameter: boolean-or-non-negative-integer preserve-job-files
     Specifies whether job files (documents) are preserved after a job is printed.  If a numeric value is specified, job files are preserved for the indicated number of seconds after printing.  Otherwise a boolean value applies indefinitely.

     Defaults to 86400.

 -- cups-configuration parameter: boolean-or-non-negative-integer preserve-job-history
     Specifies whether the job history is preserved after a job is printed. If a numeric value is specified, the job history is preserved for the indicated number of seconds after printing.  If #t, the job history is preserved until the MaxJobs limit is reached.

     Defaults to #t.

 -- cups-configuration parameter: non-negative-integer reload-timeout
     Specifies the amount of time to wait for job completion before restarting the scheduler.

     Defaults to 30.

 -- cups-configuration parameter: string rip-cache
     Specifies the maximum amount of memory to use when converting documents into bitmaps for a printer.

     Defaults to "128m".

 -- cups-configuration parameter: string server-admin
     Specifies the email address of the server administrator.

     Defaults to "root@localhost.localdomain".

 -- cups-configuration parameter: host-name-list-or-* server-alias
     The ServerAlias directive is used for HTTP Host header validation when clients connect to the scheduler from external interfaces.  Using the special name * can expose your system to known browser-based DNS rebinding attacks, even when accessing sites through a firewall.  If the auto-discovery of alternate names does not work, we recommend listing each alternate name with a ServerAlias directive instead of using *.

     Defaults to *.

 -- cups-configuration parameter: string server-name
     Specifies the fully-qualified host name of the server.

     Defaults to "localhost".

 -- cups-configuration parameter: server-tokens server-tokens
     Specifies what information is included in the Server header of HTTP responses.  None disables the Server header.  ProductOnly reports CUPS.  Major reports CUPS 2.  Minor reports CUPS 2.0.  Minimal reports CUPS 2.0.0. OS reports CUPS 2.0.0 (UNAME) where UNAME is the output of the uname command.  Full reports CUPS 2.0.0 (UNAME) IPP/2.0.

     Defaults to Minimal.

 -- cups-configuration parameter: string set-env
     Set the specified environment variable to be passed to child processes.

     Defaults to "variable value".

 -- cups-configuration parameter: multiline-string-list ssl-listen
     Listens on the specified interfaces for encrypted connections.  Valid values are of the form ADDRESS:PORT, where ADDRESS is either an IPv6 address enclosed in brackets, an IPv4 address, or * to indicate all addresses.

     Defaults to ().

 -- cups-configuration parameter: ssl-options ssl-options
     Sets encryption options.  By default, CUPS only supports encryption using TLS v1.0 or higher using known secure cipher suites.  The AllowRC4 option enables the 128-bit RC4 cipher suites, which are required for some older clients that do not implement newer ones.  The AllowSSL3 option enables SSL v3.0, which is required for some older clients that do not support TLS v1.0.

     Defaults to ().

 -- cups-configuration parameter: boolean strict-conformance?
     Specifies whether the scheduler requires clients to strictly adhere to the IPP specifications.

     Defaults to #f.

 -- cups-configuration parameter: non-negative-integer timeout
     Specifies the HTTP request timeout, in seconds.

     Defaults to 300.

 -- cups-configuration parameter: boolean web-interface?
     Specifies whether the web interface is enabled.

     Defaults to #f.

At this point you're probably thinking ``oh dear, Guix manual, I like you but you can stop already with the configuration options''.  Indeed. However, one more point: it could be that you have an existing cupsd.conf that you want to use.  In that case, you can pass an opaque-cups-configuration as the configuration of a cups-service-type.

Available opaque-cups-configuration fields are:

 -- opaque-cups-configuration parameter: package cups
     The CUPS package.

 -- opaque-cups-configuration parameter: string cupsd.conf
     The contents of the cupsd.conf, as a string.

 -- opaque-cups-configuration parameter: string cups-files.conf
     The contents of the cups-files.conf file, as a string.

For example, if your cupsd.conf and cups-files.conf are in strings of the same name, you could instantiate a CUPS service like this:

     (service cups-service-type
              (opaque-cups-configuration
                (cupsd.conf cupsd.conf)
                (cups-files.conf cups-files.conf)))

Desktop Services
................

The (gnu services desktop) module provides services that are usually useful in the context of a ``desktop'' setup---that is, on a machine running a graphical display server, possibly with graphical user interfaces, etc.  It also defines services that provide specific desktop environments like GNOME and XFCE.

To simplify things, the module defines a variable containing the set of services that users typically expect on a machine with a graphical environment and networking:

 -- Scheme Variable: %desktop-services
     This is a list of services that builds upon %BASE-SERVICES and adds or adjusts services for a typical ``desktop'' setup.

     In particular, it adds a graphical login manager (see slim-service), screen lockers, a network management tool (see wicd-service), energy and color management services, the elogind login and seat manager, the Polkit privilege service, the GeoClue location service, an NTP client (see Networking Services), the Avahi daemon, and has the name service switch service configured to be able to use nss-mdns (see mDNS).

The %DESKTOP-SERVICES variable can be used as the services field of an operating-system declaration (see services).

Additionally, the gnome-desktop-service and xfce-desktop-service procedures can add GNOME and/or XFCE to a system.  To ``add GNOME'' means that system-level services like the backlight adjustment helpers and the power management utilities are added to the system, extending polkit and dbus appropriately, allowing GNOME to operate with elevated privileges on a limited number of special-purpose system interfaces.  Additionally, adding a service made by gnome-desktop-service adds the GNOME metapackage to the system profile.  Likewise, adding the XFCE service not only adds the xfce metapackage to the system profile, but it also gives the Thunar file manager the ability to open a ``root-mode'' file management window, if the user authenticates using the administrator's password via the standard polkit graphical interface.

 -- Scheme Procedure: gnome-desktop-service
     Return a service that adds the gnome package to the system profile, and extends polkit with the actions from gnome-settings-daemon.

 -- Scheme Procedure: xfce-desktop-service
     Return a service that adds the xfce package to the system profile, and extends polkit with the ability for thunar to manipulate the file system as root from within a user session, after the user has authenticated with the administrator's password.

Because the GNOME and XFCE desktop services pull in so many packages, the default %desktop-services variable doesn't include either of them by default.  To add GNOME or XFCE, just cons them onto %desktop-services in the services field of your operating-system:

     (use-modules (gnu))
     (use-service-modules desktop)
     (operating-system
       ...
       ;; cons* adds items to the list given as its last argument.
       (services (cons* (gnome-desktop-service)
                        (xfce-desktop-service)
                        %desktop-services))
       ...)

These desktop environments will then be available as options in the graphical login window.

The actual service definitions included in %desktop-services and provided by (gnu services dbus) and (gnu services desktop) are described below.

 -- Scheme Procedure: dbus-service [#:dbus DBUS] [#:services '()]
     Return a service that runs the ``system bus'', using DBUS, with support for SERVICES.

     D-Bus (http://dbus.freedesktop.org/) is an inter-process communication facility.  Its system bus is used to allow system services to communicate and to be notified of system-wide events.

     SERVICES must be a list of packages that provide an etc/dbus-1/system.d directory containing additional D-Bus configuration and policy files.  For example, to allow avahi-daemon to use the system bus, SERVICES must be equal to (list avahi).

 -- Scheme Procedure: elogind-service [#:config CONFIG]
     Return a service that runs the elogind login and seat management daemon.  Elogind (https://github.com/andywingo/elogind) exposes a D-Bus interface that can be used to know which users are logged in, know what kind of sessions they have open, suspend the system, inhibit system suspend, reboot the system, and other tasks.

     Elogind handles most system-level power events for a computer, for example suspending the system when a lid is closed, or shutting it down when the power button is pressed.

     The CONFIG keyword argument specifies the configuration for elogind, and should be the result of an (elogind-configuration (PARAMETER VALUE)...) invocation.  Available parameters and their default values are:

     kill-user-processes?
          #f

     kill-only-users
          ()

     kill-exclude-users
          ("root")

     inhibit-delay-max-seconds
          5

     handle-power-key
          poweroff

     handle-suspend-key
          suspend

     handle-hibernate-key
          hibernate

     handle-lid-switch
          suspend

     handle-lid-switch-docked
          ignore

     power-key-ignore-inhibited?
          #f

     suspend-key-ignore-inhibited?
          #f

     hibernate-key-ignore-inhibited?
          #f

     lid-switch-ignore-inhibited?
          #t

     holdoff-timeout-seconds
          30

     idle-action
          ignore

     idle-action-seconds
          (* 30 60)

     runtime-directory-size-percent
          10

     runtime-directory-size
          #f

     remove-ipc?
          #t

     suspend-state
          ("mem" "standby" "freeze")

     suspend-mode
          ()

     hibernate-state
          ("disk")

     hibernate-mode
          ("platform" "shutdown")

     hybrid-sleep-state
          ("disk")

     hybrid-sleep-mode
          ("suspend" "platform" "shutdown")

 -- Scheme Procedure: polkit-service
     [#:polkit POLKIT]
     Return a service that runs the Polkit privilege management service (http://www.freedesktop.org/wiki/Software/polkit/), which allows system administrators to grant access to privileged operations in a structured way.  By querying the Polkit service, a privileged system component can know when it should grant additional capabilities to ordinary users.  For example, an ordinary user can be granted the capability to suspend the system if the user is logged in locally.

 -- Scheme Procedure: upower-service [#:upower UPOWER]
     [#:watts-up-pro? #f]
     [#:poll-batteries? #t]
     [#:ignore-lid? #f]
     [#:use-percentage-for-policy? #f]
     [#:percentage-low 10]
     [#:percentage-critical 3]
     [#:percentage-action 2]
     [#:time-low 1200]
     [#:time-critical 300]
     [#:time-action 120]
     [#:critical-power-action 'hybrid-sleep]
     Return a service that runs upowerd (http://upower.freedesktop.org/), a system-wide monitor for power consumption and battery levels, with the given configuration settings.  It implements the org.freedesktop.UPower D-Bus interface, and is notably used by GNOME.

 -- Scheme Procedure: udisks-service [#:udisks UDISKS]
     Return a service for UDisks (http://udisks.freedesktop.org/docs/latest/), a disk management daemon that provides user interfaces with notifications and ways to mount/unmount disks.  Programs that talk to UDisks include the udisksctl command, part of UDisks, and GNOME Disks.

 -- Scheme Procedure: colord-service [#:colord COLORD]
     Return a service that runs colord, a system service with a D-Bus interface to manage the color profiles of input and output devices such as screens and scanners.  It is notably used by the GNOME Color Manager graphical tool.  See the colord web site (http://www.freedesktop.org/software/colord/) for more information.

 -- Scheme Procedure: geoclue-application name [#:allowed? #t] [#:system? #f] [#:users '()]
     Return a configuration allowing an application to access GeoClue location data.  NAME is the Desktop ID of the application, without the .desktop part.  If ALLOWED? is true, the application will have access to location information by default.  The boolean SYSTEM?  value indicates whether an application is a system component or not.  Finally USERS is a list of UIDs of all users for which this application is allowed location info access.  An empty users list means that all users are allowed.

 -- Scheme Variable: %standard-geoclue-applications
     The standard list of well-known GeoClue application configurations, granting authority to the GNOME date-and-time utility to ask for the current location in order to set the time zone, and allowing the IceCat and Epiphany web browsers to request location information. IceCat and Epiphany both query the user before allowing a web page to know the user's location.

 -- Scheme Procedure: geoclue-service [#:colord COLORD]
     [#:whitelist '()]
     [#:wifi-geolocation-url "https://location.services.mozilla.com/v1/geolocate?key=geoclue"]
     [#:submit-data? #f]
     [#:wifi-submission-url "https://location.services.mozilla.com/v1/submit?key=geoclue"] [#:submission-nick "geoclue"] [#:applications %standard-geoclue-applications] Return a service that runs the GeoClue location service.  This service provides a D-Bus interface to allow applications to request access to a user's physical location, and optionally to add information to online location databases.  See the GeoClue web site (https://wiki.freedesktop.org/www/Software/GeoClue/) for more information.

 -- Scheme Procedure: bluetooth-service [#:bluez BLUEZ]
     Return a service that runs the bluetoothd daemon, which manages all the Bluetooth devices and provides a number of D-Bus interfaces.

     Users need to be in the lp group to access the D-Bus service.

Database Services
.................

The (gnu services databases) module provides the following services.

 -- Scheme Procedure: postgresql-service [#:postgresql postgresql]
     [#:config-file] [#:data-directory ``/var/lib/postgresql/data'']
     [#:port 5432] [#:locale ``en_US.utf8'']
     Return a service that runs POSTGRESQL, the PostgreSQL database server.

     The PostgreSQL daemon loads its runtime configuration from CONFIG-FILE, creates a database cluster with LOCALE as the default locale, stored in DATA-DIRECTORY.  It then listens on PORT.

 -- Scheme Procedure: mysql-service [#:config (mysql-configuration)]
     Return a service that runs mysqld, the MySQL or MariaDB database server.

     The optional CONFIG argument specifies the configuration for mysqld, which should be a <mysql-configuration> object.

 -- Data Type: mysql-configuration
     Data type representing the configuration of MYSQL-SERVICE.

     mysql (default: MARIADB)
          Package object of the MySQL database server, can be either MARIADB or MYSQL.

          For MySQL, a temporary root password will be displayed at activation time. For MariaDB, the root password is empty.

     port (default: 3306)
          TCP port on which the database server listens for incoming connections.

Mail Services
.............

The (gnu services mail) module provides Guix service definitions for email services: IMAP, POP3, and LMTP servers, as well as mail transport agents (MTAs).  Lots of acronyms!  These services are detailed in the subsections below.

Dovecot Service
...............

 -- Scheme Procedure: dovecot-service [#:config (dovecot-configuration)]
     Return a service that runs the Dovecot IMAP/POP3/LMTP mail server.

By default, Dovecot does not need much configuration; the default configuration object created by (dovecot-configuration) will suffice if your mail is delivered to ~/Maildir.  A self-signed certificate will be generated for TLS-protected connections, though Dovecot will also listen on cleartext ports by default.  There are a number of options, though, which mail administrators might need to change, and as is the case with other services, Guix allows the system administrator to specify these parameters via a uniform Scheme interface.

For example, to specify that mail is located at maildir~/.mail, one would instantiate the Dovecot service like this:

     (dovecot-service #:config
                      (dovecot-configuration
                       (mail-location "maildir:~/.mail")))

The available configuration parameters follow.  Each parameter definition is preceded by its type; for example, string-list foo indicates that the foo parameter should be specified as a list of strings.  There is also a way to specify the configuration as a string, if you have an old dovecot.conf file that you want to port over from some other system; see the end for more details.

Available dovecot-configuration fields are:

 -- dovecot-configuration parameter: package dovecot
     The dovecot package.

 -- dovecot-configuration parameter: comma-separated-string-list listen
     A list of IPs or hosts where to listen for connections.  * listens on all IPv4 interfaces, :: listens on all IPv6 interfaces.  If you want to specify non-default ports or anything more complex, customize the address and port fields of the inet-listener of the specific services you are interested in.

 -- dovecot-configuration parameter: protocol-configuration-list protocols
     List of protocols we want to serve.  Available protocols include imap, pop3, and lmtp.

     Available protocol-configuration fields are:

      -- protocol-configuration parameter: string name
          The name of the protocol.

      -- protocol-configuration parameter: string auth-socket-path
          UNIX socket path to the master authentication server to find users. This is used by imap (for shared users) and lda. It defaults to "/var/run/dovecot/auth-userdb".

      -- protocol-configuration parameter: space-separated-string-list mail-plugins
          Space separated list of plugins to load.

      -- protocol-configuration parameter: non-negative-integer mail-max-userip-connections
          Maximum number of IMAP connections allowed for a user from each IP address.  NOTE: The username is compared case-sensitively. Defaults to 10.

 -- dovecot-configuration parameter: service-configuration-list services
     List of services to enable.  Available services include imap, imap-login, pop3, pop3-login, auth, and lmtp.

     Available service-configuration fields are:

      -- service-configuration parameter: string kind
          The service kind.  Valid values include director, imap-login, pop3-login, lmtp, imap, pop3, auth, auth-worker, dict, tcpwrap, quota-warning, or anything else.

      -- service-configuration parameter: listener-configuration-list listeners
          Listeners for the service.  A listener is either a unix-listener-configuration, a fifo-listener-configuration, or an inet-listener-configuration. Defaults to ().

          Available unix-listener-configuration fields are:

           -- unix-listener-configuration parameter: file-name path
               The file name on which to listen.

           -- unix-listener-configuration parameter: string mode
               The access mode for the socket. Defaults to "0600".

           -- unix-listener-configuration parameter: string user
               The user to own the socket. Defaults to "".

           -- unix-listener-configuration parameter: string group
               The group to own the socket. Defaults to "".

          Available fifo-listener-configuration fields are:

           -- fifo-listener-configuration parameter: file-name path
               The file name on which to listen.

           -- fifo-listener-configuration parameter: string mode
               The access mode for the socket. Defaults to "0600".

           -- fifo-listener-configuration parameter: string user
               The user to own the socket. Defaults to "".

           -- fifo-listener-configuration parameter: string group
               The group to own the socket. Defaults to "".

          Available inet-listener-configuration fields are:

           -- inet-listener-configuration parameter: string protocol
               The protocol to listen for.

           -- inet-listener-configuration parameter: string address
               The address on which to listen, or empty for all addresses. Defaults to "".

           -- inet-listener-configuration parameter: non-negative-integer port
               The port on which to listen.

           -- inet-listener-configuration parameter: boolean ssl?
               Whether to use SSL for this service; yes, no, or required. Defaults to #t.

      -- service-configuration parameter: non-negative-integer service-count
          Number of connections to handle before starting a new process. Typically the only useful values are 0 (unlimited) or 1.  1 is more secure, but 0 is faster.  <doc/wiki/LoginProcess.txt>. Defaults to 1.

      -- service-configuration parameter: non-negative-integer process-min-avail
          Number of processes to always keep waiting for more connections. Defaults to 0.

      -- service-configuration parameter: non-negative-integer vsz-limit
          If you set service-count 0, you probably need to grow this. Defaults to 256000000.

 -- dovecot-configuration parameter: dict-configuration dict
     Dict configuration, as created by the dict-configuration constructor.

     Available dict-configuration fields are:

      -- dict-configuration parameter: free-form-fields entries
          A list of key-value pairs that this dict should hold. Defaults to ().

 -- dovecot-configuration parameter: passdb-configuration-list passdbs
     A list of passdb configurations, each one created by the passdb-configuration constructor.

     Available passdb-configuration fields are:

      -- passdb-configuration parameter: string driver
          The driver that the passdb should use.  Valid values include pam, passwd, shadow, bsdauth, and static. Defaults to "pam".

      -- passdb-configuration parameter: free-form-args args
          A list of key-value args to the passdb driver. Defaults to ().

 -- dovecot-configuration parameter: userdb-configuration-list userdbs
     List of userdb configurations, each one created by the userdb-configuration constructor.

     Available userdb-configuration fields are:

      -- userdb-configuration parameter: string driver
          The driver that the userdb should use.  Valid values include passwd and static. Defaults to "passwd".

      -- userdb-configuration parameter: free-form-args args
          A list of key-value args to the userdb driver. Defaults to ().

      -- userdb-configuration parameter: free-form-args override-fields
          Override fields from passwd. Defaults to ().

 -- dovecot-configuration parameter: plugin-configuration plugin-configuration
     Plug-in configuration, created by the plugin-configuration constructor.

 -- dovecot-configuration parameter: list-of-namespace-configuration namespaces
     List of namespaces.  Each item in the list is created by the namespace-configuration constructor.

     Available namespace-configuration fields are:

      -- namespace-configuration parameter: string name
          Name for this namespace.

      -- namespace-configuration parameter: string type
          Namespace type: private, shared or public. Defaults to "private".

      -- namespace-configuration parameter: string separator
          Hierarchy separator to use. You should use the same separator for all namespaces or some clients get confused.  / is usually a good one.  The default however depends on the underlying mail storage format. Defaults to "".

      -- namespace-configuration parameter: string prefix
          Prefix required to access this namespace.  This needs to be different for all namespaces. For example Public/. Defaults to "".

      -- namespace-configuration parameter: string location
          Physical location of the mailbox. This is in the same format as mail_location, which is also the default for it. Defaults to "".

      -- namespace-configuration parameter: boolean inbox?
          There can be only one INBOX, and this setting defines which namespace has it. Defaults to #f.

      -- namespace-configuration parameter: boolean hidden?
          If namespace is hidden, it's not advertised to clients via NAMESPACE extension. You'll most likely also want to set list? #f.  This is mostly useful when converting from another server with different namespaces which you want to deprecate but still keep working.  For example you can create hidden namespaces with prefixes ~/mail/, ~%u/mail/ and mail/. Defaults to #f.

      -- namespace-configuration parameter: boolean list?
          Show the mailboxes under this namespace with the LIST command. This makes the namespace visible for clients that do not support the NAMESPACE extension.  The special children value lists child mailboxes, but hides the namespace prefix. Defaults to #t.

      -- namespace-configuration parameter: boolean subscriptions?
          Namespace handles its own subscriptions.  If set to #f, the parent namespace handles them.  The empty prefix should always have this as #t). Defaults to #t.

      -- namespace-configuration parameter: mailbox-configuration-list mailboxes
          List of predefined mailboxes in this namespace. Defaults to ().

          Available mailbox-configuration fields are:

           -- mailbox-configuration parameter: string name
               Name for this mailbox.

           -- mailbox-configuration parameter: string auto
               create will automatically create this mailbox. subscribe will both create and subscribe to the mailbox. Defaults to "no".

           -- mailbox-configuration parameter: space-separated-string-list special-use
               List of IMAP SPECIAL-USE attributes as specified by RFC 6154. Valid values are \All, \Archive, \Drafts, \Flagged, \Junk, \Sent, and \Trash. Defaults to ().

 -- dovecot-configuration parameter: file-name base-dir
     Base directory where to store runtime data. Defaults to "/var/run/dovecot/".

 -- dovecot-configuration parameter: string login-greeting
     Greeting message for clients. Defaults to "Dovecot ready.".

 -- dovecot-configuration parameter: space-separated-string-list login-trusted-networks
     List of trusted network ranges.  Connections from these IPs are allowed to override their IP addresses and ports (for logging and for authentication checks).  disable-plaintext-auth is also ignored for these networks.  Typically you would specify your IMAP proxy servers here. Defaults to ().

 -- dovecot-configuration parameter: space-separated-string-list login-access-sockets
     List of login access check sockets (e.g. tcpwrap). Defaults to ().

 -- dovecot-configuration parameter: boolean verbose-proctitle?
     Show more verbose process titles (in ps).  Currently shows user name and IP address.  Useful for seeing who is actually using the IMAP processes (e.g. shared mailboxes or if the same uid is used for multiple accounts). Defaults to #f.

 -- dovecot-configuration parameter: boolean shutdown-clients?
     Should all processes be killed when Dovecot master process shuts down. Setting this to #f means that Dovecot can be upgraded without forcing existing client connections to close (although that could also be a problem if the upgrade is e.g. due to a security fix). Defaults to #t.

 -- dovecot-configuration parameter: non-negative-integer doveadm-worker-count
     If non-zero, run mail commands via this many connections to doveadm server, instead of running them directly in the same process. Defaults to 0.

 -- dovecot-configuration parameter: string doveadm-socket-path
     UNIX socket or host:port used for connecting to doveadm server. Defaults to "doveadm-server".

 -- dovecot-configuration parameter: space-separated-string-list import-environment
     List of environment variables that are preserved on Dovecot startup and passed down to all of its child processes.  You can also give key=value pairs to always set specific settings.

 -- dovecot-configuration parameter: boolean disable-plaintext-auth?
     Disable LOGIN command and all other plaintext authentications unless SSL/TLS is used (LOGINDISABLED capability).  Note that if the remote IP matches the local IP (i.e. you're connecting from the same computer), the connection is considered secure and plaintext authentication is allowed.  See also ssl=required setting. Defaults to #t.

 -- dovecot-configuration parameter: non-negative-integer auth-cache-size
     Authentication cache size (e.g. #e10e6).  0 means it's disabled. Note that bsdauth, PAM and vpopmail require cache-key to be set for caching to be used. Defaults to 0.

 -- dovecot-configuration parameter: string auth-cache-ttl
     Time to live for cached data.  After TTL expires the cached record is no longer used, *except* if the main database lookup returns internal failure.  We also try to handle password changes automatically: If user's previous authentication was successful, but this one wasn't, the cache isn't used.  For now this works only with plaintext authentication. Defaults to "1 hour".

 -- dovecot-configuration parameter: string auth-cache-negative-ttl
     TTL for negative hits (user not found, password mismatch). 0 disables caching them completely. Defaults to "1 hour".

 -- dovecot-configuration parameter: space-separated-string-list auth-realms
     List of realms for SASL authentication mechanisms that need them. You can leave it empty if you don't want to support multiple realms. Many clients simply use the first one listed here, so keep the default realm first. Defaults to ().

 -- dovecot-configuration parameter: string auth-default-realm
     Default realm/domain to use if none was specified.  This is used for both SASL realms and appending @domain to username in plaintext logins. Defaults to "".

 -- dovecot-configuration parameter: string auth-username-chars
     List of allowed characters in username.  If the user-given username contains a character not listed in here, the login automatically fails. This is just an extra check to make sure user can't exploit any potential quote escaping vulnerabilities with SQL/LDAP databases.  If you want to allow all characters, set this value to empty. Defaults to "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ01234567890.-_@".

 -- dovecot-configuration parameter: string auth-username-translation
     Username character translations before it's looked up from databases.  The value contains series of from -> to characters.  For example #@/@ means that # and / characters are translated to @. Defaults to "".

 -- dovecot-configuration parameter: string auth-username-format
     Username formatting before it's looked up from databases.  You can use the standard variables here, e.g. %Lu would lowercase the username, %n would drop away the domain if it was given, or %n-AT-%d would change the @ into -AT-.  This translation is done after auth-username-translation changes. Defaults to "%Lu".

 -- dovecot-configuration parameter: string auth-master-user-separator
     If you want to allow master users to log in by specifying the master username within the normal username string (i.e. not using SASL mechanism's support for it), you can specify the separator character here.  The format is then <username><separator><master username>. UW-IMAP uses * as the separator, so that could be a good choice. Defaults to "".

 -- dovecot-configuration parameter: string auth-anonymous-username
     Username to use for users logging in with ANONYMOUS SASL mechanism. Defaults to "anonymous".

 -- dovecot-configuration parameter: non-negative-integer auth-worker-max-count
     Maximum number of dovecot-auth worker processes.  They're used to execute blocking passdb and userdb queries (e.g. MySQL and PAM). They're automatically created and destroyed as needed. Defaults to 30.

 -- dovecot-configuration parameter: string auth-gssapi-hostname
     Host name to use in GSSAPI principal names.  The default is to use the name returned by gethostname().  Use $ALL (with quotes) to allow all keytab entries. Defaults to "".

 -- dovecot-configuration parameter: string auth-krb5-keytab
     Kerberos keytab to use for the GSSAPI mechanism.  Will use the system default (usually /etc/krb5.keytab) if not specified.  You may need to change the auth service to run as root to be able to read this file. Defaults to "".

 -- dovecot-configuration parameter: boolean auth-use-winbind?
     Do NTLM and GSS-SPNEGO authentication using Samba's winbind daemon and ntlm-auth helper. <doc/wiki/Authentication/Mechanisms/Winbind.txt>. Defaults to #f.

 -- dovecot-configuration parameter: file-name auth-winbind-helper-path
     Path for Samba's ntlm-auth helper binary. Defaults to "/usr/bin/ntlm_auth".

 -- dovecot-configuration parameter: string auth-failure-delay
     Time to delay before replying to failed authentications. Defaults to "2 secs".

 -- dovecot-configuration parameter: boolean auth-ssl-require-client-cert?
     Require a valid SSL client certificate or the authentication fails. Defaults to #f.

 -- dovecot-configuration parameter: boolean auth-ssl-username-from-cert?
     Take the username from client's SSL certificate, using X509_NAME_get_text_by_NID() which returns the subject's DN's CommonName. Defaults to #f.

 -- dovecot-configuration parameter: space-separated-string-list auth-mechanisms
     List of wanted authentication mechanisms.  Supported mechanisms are: plain, login, digest-md5, cram-md5, ntlm, rpa, apop, anonymous, gssapi, otp, skey, and gss-spnego.  NOTE: See also disable-plaintext-auth setting.

 -- dovecot-configuration parameter: space-separated-string-list director-servers
     List of IPs or hostnames to all director servers, including ourself. Ports can be specified as ip:port.  The default port is the same as what director service's inet-listener is using. Defaults to ().

 -- dovecot-configuration parameter: space-separated-string-list director-mail-servers
     List of IPs or hostnames to all backend mail servers.  Ranges are allowed too, like 10.0.0.10-10.0.0.30. Defaults to ().

 -- dovecot-configuration parameter: string director-user-expire
     How long to redirect users to a specific server after it no longer has any connections. Defaults to "15 min".

 -- dovecot-configuration parameter: non-negative-integer director-doveadm-port
     TCP/IP port that accepts doveadm connections (instead of director connections) If you enable this, you'll also need to add inet-listener for the port. Defaults to 0.

 -- dovecot-configuration parameter: string director-username-hash
     How the username is translated before being hashed.  Useful values include %Ln if user can log in with or without @domain, %Ld if mailboxes are shared within domain. Defaults to "%Lu".

 -- dovecot-configuration parameter: string log-path
     Log file to use for error messages.  syslog logs to syslog, /dev/stderr logs to stderr. Defaults to "syslog".

 -- dovecot-configuration parameter: string info-log-path
     Log file to use for informational messages.  Defaults to log-path. Defaults to "".

 -- dovecot-configuration parameter: string debug-log-path
     Log file to use for debug messages.  Defaults to info-log-path. Defaults to "".

 -- dovecot-configuration parameter: string syslog-facility
     Syslog facility to use if you're logging to syslog.  Usually if you don't want to use mail, you'll use local0..local7.  Also other standard facilities are supported. Defaults to "mail".

 -- dovecot-configuration parameter: boolean auth-verbose?
     Log unsuccessful authentication attempts and the reasons why they failed. Defaults to #f.

 -- dovecot-configuration parameter: boolean auth-verbose-passwords?
     In case of password mismatches, log the attempted password.  Valid values are no, plain and sha1.  sha1 can be useful for detecting brute force password attempts vs.  user simply trying the same password over and over again.  You can also truncate the value to n chars by appending ":n" (e.g. sha1:6). Defaults to #f.

 -- dovecot-configuration parameter: boolean auth-debug?
     Even more verbose logging for debugging purposes.  Shows for example SQL queries. Defaults to #f.

 -- dovecot-configuration parameter: boolean auth-debug-passwords?
     In case of password mismatches, log the passwords and used scheme so the problem can be debugged.  Enabling this also enables auth-debug. Defaults to #f.

 -- dovecot-configuration parameter: boolean mail-debug?
     Enable mail process debugging.  This can help you figure out why Dovecot isn't finding your mails. Defaults to #f.

 -- dovecot-configuration parameter: boolean verbose-ssl?
     Show protocol level SSL errors. Defaults to #f.

 -- dovecot-configuration parameter: string log-timestamp
     Prefix for each line written to log file.  % codes are in strftime(3) format. Defaults to "\"%b %d %H:%M:%S \"".

 -- dovecot-configuration parameter: space-separated-string-list login-log-format-elements
     List of elements we want to log.  The elements which have a non-empty variable value are joined together to form a comma-separated string.

 -- dovecot-configuration parameter: string login-log-format
     Login log format.  %s contains login-log-format-elements string, %$ contains the data we want to log. Defaults to "%$: %s".

 -- dovecot-configuration parameter: string mail-log-prefix
     Log prefix for mail processes.  See doc/wiki/Variables.txt for list of possible variables you can use. Defaults to "\"%s(%u): \"".

 -- dovecot-configuration parameter: string deliver-log-format
     Format to use for logging mail deliveries.  You can use variables:

     %$
          Delivery status message (e.g. saved to INBOX)

     %m
          Message-ID

     %s
          Subject

     %f
          From address

     %p
          Physical size

     %w
          Virtual size.

     Defaults to "msgid=%m: %$".

 -- dovecot-configuration parameter: string mail-location
     Location for users' mailboxes.  The default is empty, which means that Dovecot tries to find the mailboxes automatically.  This won't work if the user doesn't yet have any mail, so you should explicitly tell Dovecot the full location.

     If you're using mbox, giving a path to the INBOX file (e.g. /var/mail/%u) isn't enough.  You'll also need to tell Dovecot where the other mailboxes are kept.  This is called the "root mail directory", and it must be the first path given in the mail-location setting.

     There are a few special variables you can use, eg.:

     %u
          username

     %n
          user part in user@domain, same as %u if there's no domain

     %d
          domain part in user@domain, empty if there's no domain

     %h
          home director

     See doc/wiki/Variables.txt for full list.  Some examples:

     maildir:~/Maildir

     mbox:~/mail:INBOX=/var/mail/%u

     mbox:/var/mail/%d/%1n/%n:INDEX=/var/indexes/%d/%1n/%

     Defaults to "".

 -- dovecot-configuration parameter: string mail-uid
     System user and group used to access mails.  If you use multiple, userdb can override these by returning uid or gid fields.  You can use either numbers or names.  <doc/wiki/UserIds.txt>. Defaults to "".

 -- dovecot-configuration parameter: string mail-gid

     Defaults to "".

 -- dovecot-configuration parameter: string mail-privileged-group
     Group to enable temporarily for privileged operations.  Currently this is used only with INBOX when either its initial creation or dotlocking fails.  Typically this is set to "mail" to give access to /var/mail. Defaults to "".

 -- dovecot-configuration parameter: string mail-access-groups
     Grant access to these supplementary groups for mail processes. Typically these are used to set up access to shared mailboxes.  Note that it may be dangerous to set these if users can create symlinks (e.g. if "mail" group is set here, ln -s /var/mail ~/mail/var could allow a user to delete others' mailboxes, or ln -s /secret/shared/box ~/mail/mybox would allow reading it). Defaults to "".

 -- dovecot-configuration parameter: boolean mail-full-filesystem-access?
     Allow full file system access to clients.  There's no access checks other than what the operating system does for the active UID/GID.  It works with both maildir and mboxes, allowing you to prefix mailboxes names with e.g. /path/ or ~user/. Defaults to #f.

 -- dovecot-configuration parameter: boolean mmap-disable?
     Don't use mmap() at all.  This is required if you store indexes to shared file systems (NFS or clustered file system). Defaults to #f.

 -- dovecot-configuration parameter: boolean dotlock-use-excl?
     Rely on O_EXCL to work when creating dotlock files.  NFS supports O_EXCL since version 3, so this should be safe to use nowadays by default. Defaults to #t.

 -- dovecot-configuration parameter: string mail-fsync
     When to use fsync() or fdatasync() calls:

     optimized
          Whenever necessary to avoid losing important data

     always
          Useful with e.g. NFS when write()s are delayed

     never
          Never use it (best performance, but crashes can lose data).

     Defaults to "optimized".

 -- dovecot-configuration parameter: boolean mail-nfs-storage?
     Mail storage exists in NFS.  Set this to yes to make Dovecot flush NFS caches whenever needed.  If you're using only a single mail server this isn't needed. Defaults to #f.

 -- dovecot-configuration parameter: boolean mail-nfs-index?
     Mail index files also exist in NFS.  Setting this to yes requires mmap-disable? #t and fsync-disable? #f. Defaults to #f.

 -- dovecot-configuration parameter: string lock-method
     Locking method for index files.  Alternatives are fcntl, flock and dotlock.  Dotlocking uses some tricks which may create more disk I/O than other locking methods.  NFS users: flock doesn't work, remember to change mmap-disable. Defaults to "fcntl".

 -- dovecot-configuration parameter: file-name mail-temp-dir
     Directory in which LDA/LMTP temporarily stores incoming mails >128 kB. Defaults to "/tmp".

 -- dovecot-configuration parameter: non-negative-integer first-valid-uid
     Valid UID range for users.  This is mostly to make sure that users can't log in as daemons or other system users.  Note that denying root logins is hardcoded to dovecot binary and can't be done even if first-valid-uid is set to 0. Defaults to 500.

 -- dovecot-configuration parameter: non-negative-integer last-valid-uid

     Defaults to 0.

 -- dovecot-configuration parameter: non-negative-integer first-valid-gid
     Valid GID range for users.  Users having non-valid GID as primary group ID aren't allowed to log in.  If user belongs to supplementary groups with non-valid GIDs, those groups are not set. Defaults to 1.

 -- dovecot-configuration parameter: non-negative-integer last-valid-gid

     Defaults to 0.

 -- dovecot-configuration parameter: non-negative-integer mail-max-keyword-length
     Maximum allowed length for mail keyword name.  It's only forced when trying to create new keywords. Defaults to 50.

 -- dovecot-configuration parameter: colon-separated-file-name-list valid-chroot-dirs
     List of directories under which chrooting is allowed for mail processes (i.e. /var/mail will allow chrooting to /var/mail/foo/bar too).  This setting doesn't affect login-chroot mail-chroot or auth chroot settings.  If this setting is empty, "/./" in home dirs are ignored.  WARNING: Never add directories here which local users can modify, that may lead to root exploit.  Usually this should be done only if you don't allow shell access for users. <doc/wiki/Chrooting.txt>. Defaults to ().

 -- dovecot-configuration parameter: string mail-chroot
     Default chroot directory for mail processes.  This can be overridden for specific users in user database by giving /./ in user's home directory (e.g. /home/./user chroots into /home).  Note that usually there is no real need to do chrooting, Dovecot doesn't allow users to access files outside their mail directory anyway.  If your home directories are prefixed with the chroot directory, append "/." to mail-chroot.  <doc/wiki/Chrooting.txt>. Defaults to "".

 -- dovecot-configuration parameter: file-name auth-socket-path
     UNIX socket path to master authentication server to find users. This is used by imap (for shared users) and lda. Defaults to "/var/run/dovecot/auth-userdb".

 -- dovecot-configuration parameter: file-name mail-plugin-dir
     Directory where to look up mail plugins. Defaults to "/usr/lib/dovecot".

 -- dovecot-configuration parameter: space-separated-string-list mail-plugins
     List of plugins to load for all services.  Plugins specific to IMAP, LDA, etc. are added to this list in their own .conf files. Defaults to ().

 -- dovecot-configuration parameter: non-negative-integer mail-cache-min-mail-count
     The minimum number of mails in a mailbox before updates are done to cache file.  This allows optimizing Dovecot's behavior to do less disk writes at the cost of more disk reads. Defaults to 0.

 -- dovecot-configuration parameter: string mailbox-idle-check-interval
     When IDLE command is running, mailbox is checked once in a while to see if there are any new mails or other changes.  This setting defines the minimum time to wait between those checks.  Dovecot can also use dnotify, inotify and kqueue to find out immediately when changes occur. Defaults to "30 secs".

 -- dovecot-configuration parameter: boolean mail-save-crlf?
     Save mails with CR+LF instead of plain LF.  This makes sending those mails take less CPU, especially with sendfile() syscall with Linux and FreeBSD.  But it also creates a bit more disk I/O which may just make it slower.  Also note that if other software reads the mboxes/maildirs, they may handle the extra CRs wrong and cause problems. Defaults to #f.

 -- dovecot-configuration parameter: boolean maildir-stat-dirs?
     By default LIST command returns all entries in maildir beginning with a dot.  Enabling this option makes Dovecot return only entries which are directories.  This is done by stat()ing each entry, so it causes more disk I/O. (For systems setting struct dirent->d_type this check is free and it's done always regardless of this setting). Defaults to #f.

 -- dovecot-configuration parameter: boolean maildir-copy-with-hardlinks?
     When copying a message, do it with hard links whenever possible. This makes the performance much better, and it's unlikely to have any side effects. Defaults to #t.

 -- dovecot-configuration parameter: boolean maildir-very-dirty-syncs?
     Assume Dovecot is the only MUA accessing Maildir: Scan cur/ directory only when its mtime changes unexpectedly or when we can't find the mail otherwise. Defaults to #f.

 -- dovecot-configuration parameter: space-separated-string-list mbox-read-locks
     Which locking methods to use for locking mbox.  There are four available:

     dotlock
          Create <mailbox>.lock file.  This is the oldest and most NFS-safe solution.  If you want to use /var/mail/ like directory, the users will need write access to that directory.

     dotlock-try
          Same as dotlock, but if it fails because of permissions or because there isn't enough disk space, just skip it.

     fcntl
          Use this if possible.  Works with NFS too if lockd is used.

     flock
          May not exist in all systems.  Doesn't work with NFS.

     lockf
          May not exist in all systems.  Doesn't work with NFS.

     You can use multiple locking methods; if you do the order they're declared in is important to avoid deadlocks if other MTAs/MUAs are using multiple locking methods as well.  Some operating systems don't allow using some of them simultaneously.

 -- dovecot-configuration parameter: space-separated-string-list mbox-write-locks

 -- dovecot-configuration parameter: string mbox-lock-timeout
     Maximum time to wait for lock (all of them) before aborting. Defaults to "5 mins".

 -- dovecot-configuration parameter: string mbox-dotlock-change-timeout
     If dotlock exists but the mailbox isn't modified in any way, override the lock file after this much time. Defaults to "2 mins".

 -- dovecot-configuration parameter: boolean mbox-dirty-syncs?
     When mbox changes unexpectedly we have to fully read it to find out what changed.  If the mbox is large this can take a long time.  Since the change is usually just a newly appended mail, it'd be faster to simply read the new mails.  If this setting is enabled, Dovecot does this but still safely fallbacks to re-reading the whole mbox file whenever something in mbox isn't how it's expected to be.  The only real downside to this setting is that if some other MUA changes message flags, Dovecot doesn't notice it immediately.  Note that a full sync is done with SELECT, EXAMINE, EXPUNGE and CHECK commands. Defaults to #t.

 -- dovecot-configuration parameter: boolean mbox-very-dirty-syncs?
     Like mbox-dirty-syncs, but don't do full syncs even with SELECT, EXAMINE, EXPUNGE or CHECK commands.  If this is set, mbox-dirty-syncs is ignored. Defaults to #f.

 -- dovecot-configuration parameter: boolean mbox-lazy-writes?
     Delay writing mbox headers until doing a full write sync (EXPUNGE and CHECK commands and when closing the mailbox).  This is especially useful for POP3 where clients often delete all mails.  The downside is that our changes aren't immediately visible to other MUAs. Defaults to #t.

 -- dovecot-configuration parameter: non-negative-integer mbox-min-index-size
     If mbox size is smaller than this (e.g. 100k), don't write index files.  If an index file already exists it's still read, just not updated. Defaults to 0.

 -- dovecot-configuration parameter: non-negative-integer mdbox-rotate-size
     Maximum dbox file size until it's rotated. Defaults to 2000000.

 -- dovecot-configuration parameter: string mdbox-rotate-interval
     Maximum dbox file age until it's rotated.  Typically in days.  Day begins from midnight, so 1d = today, 2d = yesterday, etc.  0 = check disabled. Defaults to "1d".

 -- dovecot-configuration parameter: boolean mdbox-preallocate-space?
     When creating new mdbox files, immediately preallocate their size to mdbox-rotate-size.  This setting currently works only in Linux with some file systems (ext4, xfs). Defaults to #f.

 -- dovecot-configuration parameter: string mail-attachment-dir
     sdbox and mdbox support saving mail attachments to external files, which also allows single instance storage for them.  Other backends don't support this for now.

     WARNING: This feature hasn't been tested much yet.  Use at your own risk.

     Directory root where to store mail attachments.  Disabled, if empty. Defaults to "".

 -- dovecot-configuration parameter: non-negative-integer mail-attachment-min-size
     Attachments smaller than this aren't saved externally.  It's also possible to write a plugin to disable saving specific attachments externally. Defaults to 128000.

 -- dovecot-configuration parameter: string mail-attachment-fs
     File system backend to use for saving attachments:

     posix
          No SiS done by Dovecot (but this might help FS's own deduplication)

     sis posix
          SiS with immediate byte-by-byte comparison during saving

     sis-queue posix
          SiS with delayed comparison and deduplication.

     Defaults to "sis posix".

 -- dovecot-configuration parameter: string mail-attachment-hash
     Hash format to use in attachment filenames.  You can add any text and variables: %{md4}, %{md5}, %{sha1}, %{sha256}, %{sha512}, %{size}.  Variables can be truncated, e.g. %{sha256:80} returns only first 80 bits. Defaults to "%{sha1}".

 -- dovecot-configuration parameter: non-negative-integer default-process-limit

     Defaults to 100.

 -- dovecot-configuration parameter: non-negative-integer default-client-limit

     Defaults to 1000.

 -- dovecot-configuration parameter: non-negative-integer default-vsz-limit
     Default VSZ (virtual memory size) limit for service processes. This is mainly intended to catch and kill processes that leak memory before they eat up everything. Defaults to 256000000.

 -- dovecot-configuration parameter: string default-login-user
     Login user is internally used by login processes.  This is the most untrusted user in Dovecot system.  It shouldn't have access to anything at all. Defaults to "dovenull".

 -- dovecot-configuration parameter: string default-internal-user
     Internal user is used by unprivileged processes.  It should be separate from login user, so that login processes can't disturb other processes. Defaults to "dovecot".

 -- dovecot-configuration parameter: string ssl?
     SSL/TLS support: yes, no, required.  <doc/wiki/SSL.txt>. Defaults to "required".

 -- dovecot-configuration parameter: string ssl-cert
     PEM encoded X.509 SSL/TLS certificate (public key). Defaults to "</etc/dovecot/default.pem".

 -- dovecot-configuration parameter: string ssl-key
     PEM encoded SSL/TLS private key.  The key is opened before dropping root privileges, so keep the key file unreadable by anyone but root. Defaults to "</etc/dovecot/private/default.pem".

 -- dovecot-configuration parameter: string ssl-key-password
     If key file is password protected, give the password here. Alternatively give it when starting dovecot with -p parameter.  Since this file is often world-readable, you may want to place this setting instead to a different. Defaults to "".

 -- dovecot-configuration parameter: string ssl-ca
     PEM encoded trusted certificate authority.  Set this only if you intend to use ssl-verify-client-cert? #t.  The file should contain the CA certificate(s) followed by the matching CRL(s).  (e.g. ssl-ca </etc/ssl/certs/ca.pem). Defaults to "".

 -- dovecot-configuration parameter: boolean ssl-require-crl?
     Require that CRL check succeeds for client certificates. Defaults to #t.

 -- dovecot-configuration parameter: boolean ssl-verify-client-cert?
     Request client to send a certificate.  If you also want to require it, set auth-ssl-require-client-cert? #t in auth section. Defaults to #f.

 -- dovecot-configuration parameter: string ssl-cert-username-field
     Which field from certificate to use for username.  commonName and x500UniqueIdentifier are the usual choices.  You'll also need to set auth-ssl-username-from-cert? #t. Defaults to "commonName".

 -- dovecot-configuration parameter: hours ssl-parameters-regenerate
     How often to regenerate the SSL parameters file.  Generation is quite CPU intensive operation.  The value is in hours, 0 disables regeneration entirely. Defaults to 168.

 -- dovecot-configuration parameter: string ssl-protocols
     SSL protocols to use. Defaults to "!SSLv2".

 -- dovecot-configuration parameter: string ssl-cipher-list
     SSL ciphers to use. Defaults to "ALL:!LOW:!SSLv2:!EXP:!aNULL".

 -- dovecot-configuration parameter: string ssl-crypto-device
     SSL crypto device to use, for valid values run "openssl engine". Defaults to "".

 -- dovecot-configuration parameter: string postmaster-address
     Address to use when sending rejection mails. %d expands to recipient domain. Defaults to "postmaster@%d".

 -- dovecot-configuration parameter: string hostname
     Hostname to use in various parts of sent mails (e.g. in Message-Id) and in LMTP replies.  Default is the system's real hostname@domain. Defaults to "".

 -- dovecot-configuration parameter: boolean quota-full-tempfail?
     If user is over quota, return with temporary failure instead of bouncing the mail. Defaults to #f.

 -- dovecot-configuration parameter: file-name sendmail-path
     Binary to use for sending mails. Defaults to "/usr/sbin/sendmail".

 -- dovecot-configuration parameter: string submission-host
     If non-empty, send mails via this SMTP host[:port] instead of sendmail. Defaults to "".

 -- dovecot-configuration parameter: string rejection-subject
     Subject: header to use for rejection mails.  You can use the same variables as for rejection-reason below. Defaults to "Rejected: %s".

 -- dovecot-configuration parameter: string rejection-reason
     Human readable error message for rejection mails.  You can use variables:

     %n
          CRLF

     %r
          reason

     %s
          original subject

     %t
          recipient

     Defaults to "Your message to <%t> was automatically rejected:%n%r".

 -- dovecot-configuration parameter: string recipient-delimiter
     Delimiter character between local-part and detail in email address. Defaults to "+".

 -- dovecot-configuration parameter: string lda-original-recipient-header
     Header where the original recipient address (SMTP's RCPT TO: address) is taken from if not available elsewhere.  With dovecot-lda -a parameter overrides this.  A commonly used header for this is X-Original-To. Defaults to "".

 -- dovecot-configuration parameter: boolean lda-mailbox-autocreate?
     Should saving a mail to a nonexistent mailbox automatically create it?. Defaults to #f.

 -- dovecot-configuration parameter: boolean lda-mailbox-autosubscribe?
     Should automatically created mailboxes be also automatically subscribed?. Defaults to #f.

 -- dovecot-configuration parameter: non-negative-integer imap-max-line-length
     Maximum IMAP command line length.  Some clients generate very long command lines with huge mailboxes, so you may need to raise this if you get "Too long argument" or "IMAP command line too large" errors often. Defaults to 64000.

 -- dovecot-configuration parameter: string imap-logout-format
     IMAP logout format string:

     %i
          total number of bytes read from client

     %o
          total number of bytes sent to client.

     Defaults to "in=%i out=%o".

 -- dovecot-configuration parameter: string imap-capability
     Override the IMAP CAPABILITY response.  If the value begins with '+', add the given capabilities on top of the defaults (e.g. +XFOO XBAR). Defaults to "".

 -- dovecot-configuration parameter: string imap-idle-notify-interval
     How long to wait between "OK Still here" notifications when client is IDLEing. Defaults to "2 mins".

 -- dovecot-configuration parameter: string imap-id-send
     ID field names and values to send to clients.  Using * as the value makes Dovecot use the default value.  The following fields have default values currently: name, version, os, os-version, support-url, support-email. Defaults to "".

 -- dovecot-configuration parameter: string imap-id-log
     ID fields sent by client to log.  * means everything. Defaults to "".

 -- dovecot-configuration parameter: space-separated-string-list imap-client-workarounds
     Workarounds for various client bugs:

     delay-newmail
          Send EXISTS/RECENT new mail notifications only when replying to NOOP and CHECK commands.  Some clients ignore them otherwise, for example OSX Mail (<v2.1).  Outlook Express breaks more badly though, without this it may show user "Message no longer in server" errors.  Note that OE6 still breaks even with this workaround if synchronization is set to "Headers Only".

     tb-extra-mailbox-sep
          Thunderbird gets somehow confused with LAYOUT=fs (mbox and dbox) and adds extra / suffixes to mailbox names.  This option causes Dovecot to ignore the extra / instead of treating it as invalid mailbox name.

     tb-lsub-flags
          Show \Noselect flags for LSUB replies with LAYOUT=fs (e.g. mbox). This makes Thunderbird realize they aren't selectable and show them greyed out, instead of only later giving "not selectable" popup error.

     Defaults to ().

 -- dovecot-configuration parameter: string imap-urlauth-host
     Host allowed in URLAUTH URLs sent by client.  "*" allows all. Defaults to "".

Whew!  Lots of configuration options.  The nice thing about it though is that GuixSD has a complete interface to Dovecot's configuration language.  This allows not only a nice way to declare configurations, but also offers reflective capabilities as well: users can write code to inspect and transform configurations from within Scheme.

However, it could be that you just want to get a dovecot.conf up and running.  In that case, you can pass an opaque-dovecot-configuration as the #:config parameter to dovecot-service.  As its name indicates, an opaque configuration does not have easy reflective capabilities.

Available opaque-dovecot-configuration fields are:

 -- opaque-dovecot-configuration parameter: package dovecot
     The dovecot package.

 -- opaque-dovecot-configuration parameter: string string
     The contents of the dovecot.conf, as a string.

For example, if your dovecot.conf is just the empty string, you could instantiate a dovecot service like this:

     (dovecot-service #:config
                      (opaque-dovecot-configuration
                       (string "")))

OpenSMTPD Service
.................

 -- Scheme Variable: opensmtpd-service-type
     This is the type of the OpenSMTPD (https://www.opensmtpd.org) service, whose value should be an opensmtpd-configuration object as in this example:

          (service opensmtpd-service-type
                   (opensmtpd-configuration
                     (config-file (local-file "./my-smtpd.conf"))))

 -- Data Type: opensmtpd-configuration
     Data type regresenting the configuration of opensmtpd.

     package (default: OPENSMTPD)
          Package object of the OpenSMTPD SMTP server.

     config-file (default: %DEFAULT-OPENSMTPD-FILE)
          File-like object of the OpenSMTPD configuration file to use.  By default it listens on the loopback network interface, and allows for mail from users and daemons on the local machine, as well as permitting email to remote servers.  Run man smtpd.conf for more information.

Kerberos Services
.................

The (gnu services kerberos) module provides services relating to the authentication protocol Kerberos.

Krb5 Service
............

Programs using a Kerberos client library normally expect a configuration file in /etc/krb5.conf. This service generates such a file from a definition provided in the operating system declaration. It does not cause any daemon to be started.

No ``keytab'' files are provided by this service---you must explicitly create them. This service is known to work with the MIT client library, mit-krb5. Other implementations have not been tested.

 -- Scheme Variable: krb5-service-type
     A service type for Kerberos 5 clients.

Here is an example of its use:

     (service krb5-service-type
              (krb5-configuration
               (default-realm "EXAMPLE.COM")
               (allow-weak-crypto? #t)
               (realms (list
                        (krb5-realm
                         (name "EXAMPLE.COM")
                         (admin-server "groucho.example.com")
                         (kdc "karl.example.com"))
                        (krb5-realm
                         (name "ARGRX.EDU")
                         (admin-server "kerb-admin.argrx.edu")
                         (kdc "keys.argrx.edu"))))))

This example provides a Kerberos 5 client configuration which:

  * Recognizes two realms, viz: ``EXAMPLE.COM'' and ``ARGRX.EDU'', both of which have distinct administration servers and key distribution centers;

  * Will default to the realm ``EXAMPLE.COM'' if the realm is not explicitly specified by clients;

  * Accepts services which only support encryption types known to be weak.

The krb5-realm and krb5-configuration types have many fields. Only the most commonly used ones are described here. For a full list, and more detailed explanation of each, see the MIT krb5.conf documentation.

 -- Data Type: krb5-realm

     name
          This field is a string identifying the name of the realm. A common convention is to use the fully qualified DNS name of your organization, converted to upper case.

     admin-server
          This field is a string identifying the host where the administration server is running.

     kdc
          This field is a string identifying the key distribution center for the realm.

 -- Data Type: krb5-configuration

     allow-weak-crypto? (default: #f)
          If this flag is #t then services which only offer encryption algorithms known to be weak will be accepted.

     default-realm (default: #f)
          This field should be a string identifying the default Kerberos realm for the client. You should set this field to the name of your Kerberos realm. If this value is #f then a realm must be specified with every Kerberos principal when invoking programs such as kinit.

     realms
          This should be a non-empty list of krb5-realm objects, which clients may access. Normally, one of them will have a name field matching the default-realm field.

PAM krb5 Service
................

The pam-krb5 service allows for login authentication and password management via Kerberos. You will need this service if you want PAM enabled applications to authenticate users using Kerberos.

 -- Scheme Variable: pam-krb5-service-type
     A service type for the Kerberos 5 PAM module.

 -- Data Type: pam-krb5-configuration
     Data type representing the configuration of the Kerberos 5 PAM module This type has the following parameters:

     pam-krb5 (default: pam-krb5)
          The pam-krb5 package to use.

     minimum-uid (default: 1000)
          The smallest user ID for which Kerberos authentications should be attempted. Local accounts with lower values will silently fail to authenticate.

Web Services
............

The (gnu services web) module provides the following service:

 -- Scheme Procedure: nginx-service [#:nginx nginx]
     [#:log-directory ``/var/log/nginx'']
     [#:run-directory ``/var/run/nginx'']
     [#:vhost-list (list (nginx-vhost-configuration))]
     [#:config-file]

     Return a service that runs NGINX, the nginx web server.

     The nginx daemon loads its runtime configuration from CONFIG-FILE. Log files are written to LOG-DIRECTORY and temporary runtime data files are written to RUN-DIRECTORY.  For proper operation, these arguments should match what is in CONFIG-FILE to ensure that the directories are created when the service is activated.

     As an alternative to using a CONFIG-FILE, VHOST-LIST can be used to specify the list of virtual hosts required on the host.  For this to work, use the default value for CONFIG-FILE.

 -- Data Type: nginx-vhost-configuration
     Data type representing the configuration of an nginx virtual host. This type has the following parameters:

     http-port (default: 80)
          Nginx will listen for HTTP connection on this port.  Set it at #f if nginx should not listen for HTTP (non secure) connection for this virtual host.

     https-port (default: 443)
          Nginx will listen for HTTPS connection on this port.  Set it at #f if nginx should not listen for HTTPS (secure) connection for this virtual host.

          Note that nginx can listen for HTTP and HTTPS connections in the same virtual host.

     server-name (default: (list 'default))
          A list of server names this vhost represents. 'default represents the default vhost for connections matching no other vhost.

     root (default: "/srv/http")
          Root of the website nginx will serve.

     index (default: (list "index.html"))
          Index files to look for when clients ask for a directory.  If it cannot be found, Nginx will send the list of files in the directory.

     ssl-certificate (default: "/etc/nginx/cert.pem")
          Where to find the certificate for secure connections.  Set it to #f if you don't have a certificate or you don't want to use HTTPS.

     ssl-certificate-key (default: "/etc/nginx/key.pem")
          Where to find the private key for secure connections.  Set it to #f if you don't have a key or you don't want to use HTTPS.

     server-tokens? (default: #f)
          Whether the server should add its configuration to response.

Network File System
...................

The (gnu services nfs) module provides the following services, which are most commonly used in relation to mounting or exporting directory trees as network file systems (NFS).

RPC Bind Service
................

The RPC Bind service provides a facility to map program numbers into universal addresses. Many NFS related services use this facility.  Hence it is automatically started when a dependent service starts.

 -- Scheme Variable: rpcbind-service-type
     A service type  for the RPC portmapper daemon.

 -- Data Type: rpcbind-configuration
     Data type representing the configuration of the RPC Bind Service. This type has the following parameters:

     rpcbind (default: rpcbind)
          The rpcbind package to use.

     warm-start? (default: #t)
          If this parameter is #t, then the daemon will read a state file on startup thus reloading state information saved by a previous instance.

Pipefs Pseudo File System
.........................

The pipefs file system is used to transfer NFS related data between the kernel and user space programs.

 -- Scheme Variable: pipefs-service-type
     A service type for the pipefs pseudo file system.

 -- Data Type: pipefs-configuration
     Data type representing the configuration of the pipefs pseudo file system service. This type has the following parameters:

     mount-point (default: "/var/lib/nfs/rpc_pipefs")
          The directory to which the file system is to be attached.

GSS Daemon Service
..................

The global security system (GSS) daemon provides strong security for RPC based protocols. Before exchanging RPC requests an RPC client must establish a security context.  Typically this is done using the Kerberos command kinit or automatically at login time using PAM services (see Kerberos Services).

 -- Scheme Variable: gss-service-type
     A service type for the Global Security System (GSS) daemon.

 -- Data Type: gss-configuration
     Data type representing the configuration of the GSS daemon service. This type has the following parameters:

     nfs-utils (default: nfs-utils)
          The package in which the rpc.gssd command is to be found.

     pipefs-directory (default: "/var/lib/nfs/rpc_pipefs")
          The directory where the pipefs file system is mounted.

IDMAP Daemon Service
....................

The idmap daemon service provides mapping between user IDs and user names. Typically it is required in order to access file systems mounted via NFSv4.

 -- Scheme Variable: idmap-service-type
     A service type for the Identity Mapper (IDMAP) daemon.

 -- Data Type: idmap-configuration
     Data type representing the configuration of the IDMAP daemon service. This type has the following parameters:

     nfs-utils (default: nfs-utils)
          The package in which the rpc.idmapd command is to be found.

     pipefs-directory (default: "/var/lib/nfs/rpc_pipefs")
          The directory where the pipefs file system is mounted.

     domain (default: #f)
          The local NFSv4 domain name. This must be a string or #f. If it is #f then the daemon will use the host's fully qualified domain name.

Continuous Integration
......................

Cuirass (https://notabug.org/mthl/cuirass) is a continuous integration tool for Guix.  It can be used both for development and for providing substitutes to others (see Substitutes).

The (gnu services cuirass) module provides the following service.

 -- Scheme Procedure: cuirass-service
     [#:config (cuirass-configuration)]
     Return a service that runs cuirass.

     The #:CONFIG keyword argument specifies the configuration for cuirass, which must be a <cuirass-configuration> object, by default it doesn't provide any build job.  If you want to provide your own configuration you will most likely use the cuirass-configuration special form which returns such objects.

In order to add build jobs you will have to set the specifications field.  Here is an example of a cuirass service defining a build job based on a specification that can be found in Cuirass source tree.

     (let ((spec `((#:name . "guix")
                   (#:url . "git://git.savannah.gnu.org/guix.git")
                   (#:load-path . ".")
                   ;; Adapt to a valid absolute file name.
                   (#:file . "/.../cuirass/tests/gnu-system.scm")
                   (#:proc . hydra-jobs)
                   (#:arguments (subset . "hello"))
                   (#:branch . "master"))))
       (cuirass-service #:config (cuirass-configuration
                                  (specifications (list spec)))))

While information related to build jobs are located directly in the specifications, global settings for the cuirass process are accessible in other cuirass-configuration fields.

 -- Data Type: cuirass-configuration
     Data type representing the configuration of Cuirass.

     cache-directory (default: "")
          Location of the repository cache.

     user (default: "cuirass")
          Owner of the cuirass process.

     group (default: "cuirass")
          Owner's group of the cuirass process.

     interval (default: 60)
          Number of seconds between the poll of the repositories followed by the Cuirass jobs.

     database (default: "/var/run/cuirass/cuirass.db")
          Location of sqlite database which contains the build results and previously added specifications.

     specifications (default: '())
          A list of specifications, where a specification is an association list (see Associations Lists (GNU Guile Reference Manual)) whose keys are keywords (#:keyword-example) as shown in the example above.

     use-substitutes? (default: #f)
          This allows using substitutes to avoid building every dependencies of a job from source.

     one-shot? (default: #f)
          Only evaluate specifications and build derivations once.

Miscellaneous Services
......................

Lirc Service
............

The (gnu services lirc) module provides the following service.

 -- Scheme Procedure: lirc-service [#:lirc lirc]
     [#:device #f] [#:driver #f] [#:config-file #f]
     [#:extra-options '()]
     Return a service that runs LIRC (http://www.lirc.org), a daemon that decodes infrared signals from remote controls.

     Optionally, DEVICE, DRIVER and CONFIG-FILE (configuration file name) may be specified.  See lircd manual for details.

     Finally, EXTRA-OPTIONS is a list of additional command-line options passed to lircd.

Spice Service
.............

The (gnu services spice) module provides the following service.

 -- Scheme Procedure: spice-vdagent-service [#:spice-vdagent]
     Returns a service that runs VDAGENT (http://www.spice-space.org), a daemon that enables sharing the clipboard with a vm and setting the guest display resolution when the graphical console window resizes.

Dictionary Services
...................

The (gnu services dict) module provides the following service:

 -- Scheme Procedure: dicod-service [#:config (dicod-configuration)]
     Return a service that runs the dicod daemon, an implementation of DICT server (see Dicod (GNU Dico Manual)).

     The optional CONFIG argument specifies the configuration for dicod, which should be a <dicod-configuration> object, by default it serves the GNU Collaborative International Dictonary of English.

     You can add open localhost to your ~/.dico file to make localhost the default server for dico client (see Initialization File (GNU Dico Manual)).

 -- Data Type: dicod-configuration
     Data type representing the configuration of dicod.

     dico (default: DICO)
          Package object of the GNU Dico dictionary server.

     interfaces (default: '("LOCALHOST"))
          This is the list of IP addresses and ports and possibly socket file names to listen to (see listen directive (GNU Dico Manual)).

     databases (default: (LIST %DICOD-DATABASE:GCIDE))
          List of <dicod-database> objects denoting dictionaries to be served.

 -- Data Type: dicod-database
     Data type representing a dictionary database.

     name
          Name of the database, will be used in DICT commands.

     module
          Name of the dicod module used by this database (see Modules (GNU Dico Manual)).

     options
          List of strings or gexps representing the arguments for the module handler (see Handlers (GNU Dico Manual)).

 -- Scheme Variable: %dicod-database:gcide
     A <dicod-database> object serving the GNU Collaborative International Dictonary of English using the gcide package.

Version Control
...............

The (gnu services version-control) module provides the following services:

Git daemon service
..................

 -- Scheme Procedure: git-daemon-service [#:config (git-daemon-configuration)]

     Return a service that runs git daemon, a simple TCP server to expose repositiories over the Git protocol for annoymous access.

     The optional CONFIG argument should be a <git-daemon-configuration> object, by default it allows read-only access to exported (By creating the magic file "git-daemon-export-ok" in the repository directory.) repositories under /srv/git.

 -- Data Type: git-daemon-configuration
     Data type representing the configuration for git-daemon-service.

     package (default: GIT)
          Package object of the Git distributed version control system.

     export-all? (default: #F)
          Whether to allow access for all Git repositories, even if they do not have the git-daemon-export-ok file.

     base-path (default: /srv/git)
          Whether to remap all the path requests as relative to the given path. If you run git daemon with (BASE-PATH "/SRV/GIT") on example.com, then if you later try to pull git://example.com/hello.git, git daemon will interpret the path as /srv/git/hello.git.

     user-path (default: #F)
          Whether to allow ~user notation to be used in requests.  When specified with empty string, requests to git://host/~alice/foo is taken as a request to access foo repository in the home directory of user alice.  If (USER-PATH "PATH") is specified, the same request is taken as a request to access path/foo repository in the home directory of user alice.

     listen (default: '())
          Whether to listen on specific IP addresses or hostnames, defaults to all.

     port (default: #F)
          Whether to listen on an alternative port, which defaults to 9418.

     whitelist (default: '())
          If not empty, only allow access to this list of directories.

     extra-options (default: '())
          Extra options will be passed to git daemon, please run man git-daemon for more information.

Setuid Programs
---------------

Some programs need to run with ``root'' privileges, even when they are launched by unprivileged users.  A notorious example is the passwd program, which users can run to change their password, and which needs to access the /etc/passwd and /etc/shadow files---something normally restricted to root, for obvious security reasons.  To address that, these executables are setuid-root, meaning that they always run with root privileges (see How Change Persona (The GNU C Library Reference Manual), for more info about the setuid mechanism.)

The store itself cannot contain setuid programs: that would be a security issue since any user on the system can write derivations that populate the store (see The Store).  Thus, a different mechanism is used: instead of changing the setuid bit directly on files that are in the store, we let the system administrator declare which programs should be setuid root.

The setuid-programs field of an operating-system declaration contains a list of G-expressions denoting the names of programs to be setuid-root (see Using the Configuration System). For instance, the passwd program, which is part of the Shadow package, can be designated by this G-expression (see G-Expressions):

     #~(string-append #$shadow "/bin/passwd")

A default set of setuid programs is defined by the %setuid-programs variable of the (gnu system) module.

 -- Scheme Variable: %setuid-programs
     A list of G-expressions denoting common programs that are setuid-root.

     The list includes commands such as passwd, ping, su, and sudo.

Under the hood, the actual setuid programs are created in the /run/setuid-programs directory at system activation time.  The files in this directory refer to the ``real'' binaries, which are in the store.

X.509 Certificates
------------------

Web servers available over HTTPS (that is, HTTP over the transport-layer security mechanism, TLS) send client programs an X.509 certificate that the client can then use to authenticate the server.  To do that, clients verify that the server's certificate is signed by a so-called certificate authority (CA).  But to verify the CA's signature, clients must have first acquired the CA's certificate.

Web browsers such as GNU IceCat include their own set of CA certificates, such that they are able to verify CA signatures out-of-the-box.

However, most other programs that can talk HTTPS---wget, git, w3m, etc.---need to be told where CA certificates can be found.

In GuixSD, this is done by adding a package that provides certificates to the packages field of the operating-system declaration (see operating-system Reference).  GuixSD includes one such package, nss-certs, which is a set of CA certificates provided as part of Mozilla's Network Security Services.

Note that it is not part of %BASE-PACKAGES, so you need to explicitly add it.  The /etc/ssl/certs directory, which is where most applications and libraries look for certificates by default, points to the certificates installed globally.

Unprivileged users, including users of Guix on a foreign distro, can also install their own certificate package in their profile.  A number of environment variables need to be defined so that applications and libraries know where to find them.  Namely, the OpenSSL library honors the SSL_CERT_DIR and SSL_CERT_FILE variables.  Some applications add their own environment variables; for instance, the Git version control system honors the certificate bundle pointed to by the GIT_SSL_CAINFO environment variable.  Thus, you would typically run something like:

     $ guix package -i nss-certs
     $ export SSL_CERT_DIR="$HOME/.guix-profile/etc/ssl/certs"
     $ export SSL_CERT_FILE="$HOME/.guix-profile/etc/ssl/certs/ca-certificates.crt"
     $ export GIT_SSL_CAINFO="$SSL_CERT_FILE"

Name Service Switch
-------------------

The (gnu system nss) module provides bindings to the configuration file of the libc name service switch or NSS (see NSS Configuration File (The GNU C Library Reference Manual)).  In a nutshell, the NSS is a mechanism that allows libc to be extended with new ``name'' lookup methods for system databases, which includes host names, service names, user accounts, and more (see System Databases and Name Service Switch (The GNU C Library Reference Manual)).

The NSS configuration specifies, for each system database, which lookup method is to be used, and how the various methods are chained together---for instance, under which circumstances NSS should try the next method in the list.  The NSS configuration is given in the name-service-switch field of operating-system declarations (see name-service-switch).

As an example, the declaration below configures the NSS to use the nss-mdns back-end (http://0pointer.de/lennart/projects/nss-mdns/), which supports host name lookups over multicast DNS (mDNS) for host names ending in .local:

     (name-service-switch
        (hosts (list %files    ;first, check /etc/hosts

                     ;; If the above did not succeed, try
                     ;; with 'mdns_minimal'.
                     (name-service
                       (name "mdns_minimal")

                       ;; 'mdns_minimal' is authoritative for
                       ;; '.local'.  When it returns "not found",
                       ;; no need to try the next methods.
                       (reaction (lookup-specification
                                  (not-found => return))))

                     ;; Then fall back to DNS.
                     (name-service
                       (name "dns"))

                     ;; Finally, try with the "full" 'mdns'.
                     (name-service
                       (name "mdns")))))

Do not worry: the %mdns-host-lookup-nss variable (see below) contains this configuration, so you will not have to type it if all you want is to have .local host lookup working.

Note that, in this case, in addition to setting the name-service-switch of the operating-system declaration, you also need to use avahi-service (see avahi-service), or %DESKTOP-SERVICES, which includes it (see Desktop Services).  Doing this makes nss-mdns accessible to the name service cache daemon (see nscd-service).

For convenience, the following variables provide typical NSS configurations.

 -- Scheme Variable: %default-nss
     This is the default name service switch configuration, a name-service-switch object.

 -- Scheme Variable: %mdns-host-lookup-nss
     This is the name service switch configuration with support for host name lookup over multicast DNS (mDNS) for host names ending in .local.

The reference for name service switch configuration is given below.  It is a direct mapping of the configuration file format of the C library , so please refer to the C library manual for more information (see NSS Configuration File (The GNU C Library Reference Manual)). Compared to the configuration file format of libc NSS, it has the advantage not only of adding this warm parenthetic feel that we like, but also static checks: you will know about syntax errors and typos as soon as you run guix system.

 -- Data Type: name-service-switch

     This is the data type representation the configuration of libc's name service switch (NSS).  Each field below represents one of the supported system databases.

     aliases
     ethers
     group
     gshadow
     hosts
     initgroups
     netgroup
     networks
     password
     public-key
     rpc
     services
     shadow
          The system databases handled by the NSS.  Each of these fields must be a list of <name-service> objects (see below).

 -- Data Type: name-service

     This is the data type representing an actual name service and the associated lookup action.

     name
          A string denoting the name service (see Services in the NSS configuration (The GNU C Library Reference Manual)).

          Note that name services listed here must be visible to nscd.  This is achieved by passing the #:name-services argument to nscd-service the list of packages providing the needed name services (see nscd-service).

     reaction
          An action specified using the lookup-specification macro (see Actions in the NSS configuration (The GNU C Library Reference Manual)).  For example:

               (lookup-specification (unavailable => continue)
                                     (success => return))

Initial RAM Disk
----------------

For bootstrapping purposes, the Linux-Libre kernel is passed an initial RAM disk, or initrd.  An initrd contains a temporary root file system as well as an initialization script.  The latter is responsible for mounting the real root file system, and for loading any kernel modules that may be needed to achieve that.

The initrd field of an operating-system declaration allows you to specify which initrd you would like to use.  The (gnu system linux-initrd) module provides two ways to build an initrd: the high-level base-initrd procedure, and the low-level expression->initrd procedure.

The base-initrd procedure is intended to cover most common uses. For example, if you want to add a bunch of kernel modules to be loaded at boot time, you can define the initrd field of the operating system declaration like this:

     (initrd (lambda (file-systems . rest)
               ;; Create a standard initrd that has modules "foo.ko"
               ;; and "bar.ko", as well as their dependencies, in
               ;; addition to the modules available by default.
               (apply base-initrd file-systems
                      #:extra-modules '("foo" "bar")
                      rest)))

The base-initrd procedure also handles common use cases that involves using the system as a QEMU guest, or as a ``live'' system with volatile root file system.

The initial RAM disk produced by base-initrd honors several options passed on the Linux kernel command line (that is, arguments passed via the linux command of GRUB, or the -append option of QEMU), notably:

--load=BOOT
     Tell the initial RAM disk to load BOOT, a file containing a Scheme program, once it has mounted the root file system.

     GuixSD uses this option to yield control to a boot program that runs the service activation programs and then spawns the GNU Shepherd, the initialization system.

--root=ROOT
     Mount ROOT as the root file system.  ROOT can be a device name like /dev/sda1, a partition label, or a partition UUID.

--system=SYSTEM
     Have /run/booted-system and /run/current-system point to SYSTEM.

modprobe.blacklist=MODULES...
     Instruct the initial RAM disk as well as the modprobe command (from the kmod package) to refuse to load MODULES.  MODULES must be a comma-separated list of module names---e.g., usbkbd,9pnet.

--repl
     Start a read-eval-print loop (REPL) from the initial RAM disk before it tries to load kernel modules and to mount the root file system.  Our marketing team calls it boot-to-Guile.  The Schemer in you will love it.  See Using Guile Interactively (GNU Guile Reference Manual), for more information on Guile's REPL.

Now that you know all the features that initial RAM disks produced by base-initrd provide, here is how to use it and customize it further.

 -- Monadic Procedure: base-initrd FILE-SYSTEMS
     [#:qemu-networking? #f] [#:virtio? #t] [#:volatile-root? #f]
     [#:extra-modules '()] [#:mapped-devices '()]
     Return a monadic derivation that builds a generic initrd.  FILE-SYSTEMS is a list of file systems to be mounted by the initrd, possibly in addition to the root file system specified on the kernel command line via --root. MAPPED-DEVICES is a list of device mappings to realize before FILE-SYSTEMS are mounted (see Mapped Devices).

     When QEMU-NETWORKING? is true, set up networking with the standard QEMU parameters.  When VIRTIO? is true, load additional modules so that the initrd can be used as a QEMU guest with para-virtualized I/O drivers.

     When VOLATILE-ROOT? is true, the root file system is writable but any changes to it are lost.

     The initrd is automatically populated with all the kernel modules necessary for FILE-SYSTEMS and for the given options.  However, additional kernel modules can be listed in EXTRA-MODULES.  They will be added to the initrd, and loaded at boot time in the order in which they appear.

Needless to say, the initrds we produce and use embed a statically-linked Guile, and the initialization program is a Guile program.  That gives a lot of flexibility.  The expression->initrd procedure builds such an initrd, given the program to run in that initrd.

 -- Monadic Procedure: expression->initrd EXP
     [#:guile %guile-static-stripped] [#:name "guile-initrd"]
     Return a derivation that builds a Linux initrd (a gzipped cpio archive) containing GUILE and that evaluates EXP, a G-expression, upon booting.  All the derivations referenced by EXP are automatically copied to the initrd.

GRUB Configuration
------------------

The operating system uses GNU GRUB as its boot loader (see overview of GRUB (GNU GRUB Manual)).  It is configured using a grub-configuration declaration.  This data type is exported by the (gnu system grub) module and described below.

 -- Data Type: grub-configuration
     The type of a GRUB configuration declaration.

     device
          This is a string denoting the boot device.  It must be a device name understood by the grub-install command, such as /dev/sda or (hd0) (see Invoking grub-install (GNU GRUB Manual)).

     menu-entries (default: ())
          A possibly empty list of menu-entry objects (see below), denoting entries to appear in the GRUB boot menu, in addition to the current system entry and the entry pointing to previous system generations.

     default-entry (default: 0)
          The index of the default boot menu entry.  Index 0 is for the entry of the current system.

     timeout (default: 5)
          The number of seconds to wait for keyboard input before booting.  Set to 0 to boot immediately, and to -1 to wait indefinitely.

     theme (default: %DEFAULT-THEME)
          The grub-theme object describing the theme to use.

Should you want to list additional boot menu entries via the menu-entries field above, you will need to create them with the menu-entry form.  For example, imagine you want to be able to boot another distro (hard to imagine!), you can define a menu entry along these lines:

     (menu-entry
       (label "The Other Distro")
       (linux "/boot/old/vmlinux-2.6.32")
       (linux-arguments '("root=/dev/sda2"))
       (initrd "/boot/old/initrd"))

Details below.

 -- Data Type: menu-entry
     The type of an entry in the GRUB boot menu.

     label
          The label to show in the menu---e.g., "GNU".

     linux
          The Linux kernel image to boot, for example:

               (file-append linux-libre "/bzImage")

          It is also possible to specify a device explicitly in the file path using GRUB's device naming convention (see Naming convention (GNU GRUB manual)), for example:

               "(hd0,msdos1)/boot/vmlinuz"

          If the device is specified explicitly as above, then the device field is ignored entirely.

     linux-arguments (default: ())
          The list of extra Linux kernel command-line arguments---e.g., ("console=ttyS0").

     initrd
          A G-Expression or string denoting the file name of the initial RAM disk to use (see G-Expressions).

     device (default: #f)
          The device where the kernel and initrd are to be found---i.e., the GRUB root for this menu entry (see root (GNU GRUB manual)).

          This may be a file system label (a string), a file system UUID (a bytevector, see File Systems), or #f, in which case GRUB will search the device containing the file specified by the linux field (see search (GNU GRUB manual)).  It must not be an OS device name such as /dev/sda1.

     device-mount-point (default: "/")
          The mount point of the above device on the system.  You probably do not need to change the default value.  GuixSD uses it to strip the prefix of store file names for systems where /gnu or /gnu/store is on a separate partition.

Themes are created using the grub-theme form, which is not documented yet.

 -- Scheme Variable: %default-theme
     This is the default GRUB theme used by the operating system, with a fancy background image displaying the GNU and Guix logos.

Invoking guix system
--------------------

Once you have written an operating system declaration as seen in the previous section, it can be instantiated using the guix system command.  The synopsis is:

     guix system OPTIONS... ACTION FILE

FILE must be the name of a file containing an operating-system declaration.  ACTION specifies how the operating system is instantiated.  Currently the following values are supported:

reconfigure
     Build the operating system described in FILE, activate it, and switch to it (This action (and the related actions switch-generation and roll-back) are usable only on systems already running GuixSD.).

     This effects all the configuration specified in FILE: user accounts, system services, global package list, setuid programs, etc. The command starts system services specified in FILE that are not currently running; if a service is currently running, it does not attempt to upgrade it since this would not be possible without stopping it first.

     This command creates a new generation whose number is one greater than the current generation (as reported by guix system list-generations).  If that generation already exists, it will be overwritten.  This behavior mirrors that of guix package (see Invoking guix package).

     It also adds a GRUB menu entry for the new OS configuration, and moves entries for older configurations to a submenu---unless --no-grub is passed.

          It is highly recommended to run guix pull once before you run guix system reconfigure for the first time (see Invoking guix pull).  Failing to do that you would see an older version of Guix once reconfigure has completed.

switch-generation
     Switch to an existing system generation.  This action atomically switches the system profile to the specified system generation.  It also rearranges the system's existing GRUB menu entries.  It makes the menu entry for the specified system generation the default, and it moves the entries for the other generations to a submenu.  The next time the system boots, it will use the specified system generation.

     The target generation can be specified explicitly by its generation number.  For example, the following invocation would switch to system generation 7:

          guix system switch-generation 7

     The target generation can also be specified relative to the current generation with the form +N or -N, where +3 means ``3 generations ahead of the current generation,'' and -1 means ``1 generation prior to the current generation.''  When specifying a negative value such as -1, you must precede it with -- to prevent it from being parsed as an option.  For example:

          guix system switch-generation -- -1

     Currently, the effect of invoking this action is only to switch the system profile to an existing generation and rearrange the GRUB menu entries.  To actually start using the target system generation, you must reboot after running this action.  In the future, it will be updated to do the same things as reconfigure, like activating and deactivating services.

     This action will fail if the specified generation does not exist.

roll-back
     Switch to the preceding system generation.  The next time the system boots, it will use the preceding system generation.  This is the inverse of reconfigure, and it is exactly the same as invoking switch-generation with an argument of -1.

     Currently, as with switch-generation, you must reboot after running this action to actually start using the preceding system generation.

build
     Build the derivation of the operating system, which includes all the configuration files and programs needed to boot and run the system. This action does not actually install anything.

init
     Populate the given directory with all the files necessary to run the operating system specified in FILE.  This is useful for first-time installations of GuixSD.  For instance:

          guix system init my-os-config.scm /mnt

     copies to /mnt all the store items required by the configuration specified in my-os-config.scm.  This includes configuration files, packages, and so on.  It also creates other essential files needed for the system to operate correctly---e.g., the /etc, /var, and /run directories, and the /bin/sh file.

     This command also installs GRUB on the device specified in my-os-config, unless the --no-grub option was passed.

vm
     Build a virtual machine that contains the operating system declared in FILE, and return a script to run that virtual machine (VM). Arguments given to the script are passed to QEMU.

     The VM shares its store with the host system.

     Additional file systems can be shared between the host and the VM using the --share and --expose command-line options: the former specifies a directory to be shared with write access, while the latter provides read-only access to the shared directory.

     The example below creates a VM in which the user's home directory is accessible read-only, and where the /exchange directory is a read-write mapping of $HOME/tmp on the host:

          guix system vm my-config.scm \
             --expose=$HOME --share=$HOME/tmp=/exchange

     On GNU/Linux, the default is to boot directly to the kernel; this has the advantage of requiring only a very tiny root disk image since the store of the host can then be mounted.

     The --full-boot option forces a complete boot sequence, starting with the bootloader.  This requires more disk space since a root image containing at least the kernel, initrd, and bootloader data files must be created.  The --image-size option can be used to specify the size of the image.

vm-image
disk-image
     Return a virtual machine or disk image of the operating system declared in FILE that stands alone.  Use the --image-size option to specify the size of the image.

     When using vm-image, the returned image is in qcow2 format, which the QEMU emulator can efficiently use. See Running GuixSD in a VM, for more information on how to run the image in a virtual machine.

     When using disk-image, a raw disk image is produced; it can be copied as is to a USB stick, for instance.  Assuming /dev/sdc is the device corresponding to a USB stick, one can copy the image to it using the following command:

          # dd if=$(guix system disk-image my-os.scm) of=/dev/sdc

container
     Return a script to run the operating system declared in FILE within a container.  Containers are a set of lightweight isolation mechanisms provided by the kernel Linux-libre.  Containers are substantially less resource-demanding than full virtual machines since the kernel, shared objects, and other resources can be shared with the host system; this also means they provide thinner isolation.

     Currently, the script must be run as root in order to support more than a single user and group.  The container shares its store with the host system.

     As with the vm action (see guix system vm), additional file systems to be shared between the host and container can be specified using the --share and --expose options:

          guix system container my-config.scm \
             --expose=$HOME --share=$HOME/tmp=/exchange

          This option requires Linux-libre 3.19 or newer.

OPTIONS can contain any of the common build options (see Common Build Options).  In addition, OPTIONS can contain one of the following:

--system=SYSTEM
-s SYSTEM
     Attempt to build for SYSTEM instead of the host system type. This works as per guix build (see Invoking guix build).

--derivation
-d
     Return the derivation file name of the given operating system without building anything.

--image-size=SIZE
     For the vm-image and disk-image actions, create an image of the given SIZE.  SIZE may be a number of bytes, or it may include a unit as a suffix (see size specifications (GNU Coreutils)).

--on-error=STRATEGY
     Apply STRATEGY when an error occurs when reading FILE. STRATEGY may be one of the following:

     nothing-special
          Report the error concisely and exit.  This is the default strategy.

     backtrace
          Likewise, but also display a backtrace.

     debug
          Report the error and enter Guile's debugger.  From there, you can run commands such as ,bt to get a backtrace, ,locals to display local variable values, and more generally inspect the state of the program.  See Debug Commands (GNU Guile Reference Manual), for a list of available debugging commands.

     All the actions above, except build and init, can use KVM support in the Linux-libre kernel.  Specifically, if the machine has hardware virtualization support, the corresponding KVM kernel module should be loaded, and the /dev/kvm device node must exist and be readable and writable by the user and by the build users of the daemon (see Build Environment Setup).

Once you have built, configured, re-configured, and re-re-configured your GuixSD installation, you may find it useful to list the operating system generations available on disk---and that you can choose from the GRUB boot menu:

list-generations
     List a summary of each generation of the operating system available on disk, in a human-readable way.  This is similar to the --list-generations option of guix package (see Invoking guix package).

     Optionally, one can specify a pattern, with the same syntax that is used in guix package --list-generations, to restrict the list of generations displayed.  For instance, the following command displays generations that are up to 10 days old:

          $ guix system list-generations 10d

The guix system command has even more to offer!  The following sub-commands allow you to visualize how your system services relate to each other:

extension-graph
     Emit in Dot/Graphviz format to standard output the service extension graph of the operating system defined in FILE (see Service Composition, for more information on service extensions.)

     The command:

          $ guix system extension-graph FILE | dot -Tpdf > services.pdf

     produces a PDF file showing the extension relations among services.

shepherd-graph
     Emit in Dot/Graphviz format to standard output the dependency graph of shepherd services of the operating system defined in FILE.  See Shepherd Services, for more information and for an example graph.

Running GuixSD in a Virtual Machine
-----------------------------------

One way to run GuixSD in a virtual machine (VM) is to build a GuixSD virtual machine image using guix system vm-image (see Invoking guix system).  The returned image is in qcow2 format, which the QEMU emulator (http://qemu.org/) can efficiently use.

To run the image in QEMU, copy it out of the store (see The Store) and give yourself permission to write to the copy.  When invoking QEMU, you must choose a system emulator that is suitable for your hardware platform.  Here is a minimal QEMU invocation that will boot the result of guix system vm-image on x86_64 hardware:

     $ qemu-system-x86_64 \
        -net user -net nic,model=virtio \
        -enable-kvm -m 256 /tmp/qemu-image

Here is what each of these options means:

qemu-system-x86_64
     This specifies the hardware platform to emulate.  This should match the host.

-net user
     Enable the unprivileged user-mode network stack.  The guest OS can access the host but not vice versa.  This is the simplest way to get the guest OS online.

-net nic,model=virtio
     You must create a network interface of a given model.  If you do not create a NIC, the boot will fail.  Assuming your hardware platform is x86_64, you can get a list of available NIC models by running qemu-system-x86_64 -net nic,model=help.

-enable-kvm
     If your system has hardware virtualization extensions, enabling the virtual machine support (KVM) of the Linux kernel will make things run faster.

-m 256
     RAM available to the guest OS, in mebibytes.  Defaults to 128 MiB, which may be insufficient for some operations.

/tmp/qemu-image
     The file name of the qcow2 image.

The default run-vm.sh script that is returned by an invokation of guix system vm does not add a -net user flag by default. To get network access from within the vm add the (dhcp-client-service) to your system definition and start the VM using `guix system vm config.scm` -net user.  An important caveat of using -net user for networking is that ping will not work, because it uses the ICMP protocol.  You'll have to use a different command to check for network connectivity, like for example curl.

Connecting Through SSH
......................

To enable SSH inside a VM you need to add a SSH server like (dropbear-service) or (lsh-service) to your VM.  The (lsh-service) doesn't currently boot unsupervised.  It requires you to type some characters to initialize the randomness generator.  In addition you need to forward the SSH port, 22 by default, to the host.  You can do this with

     `guix system vm config.scm` -net user,hostfwd=tcp::10022-:22

To connect to the VM you can run

     ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no -p 10022

The -p tells ssh the port you want to connect to. -o UserKnownHostsFile=/dev/null prevents ssh from complaining every time you modify your config.scm file and the -o StrictHostKeyChecking=no prevents you from having to allow a connection to an unknown host every time you connect.

Using virt-viewer with Spice
............................

As an alternative to the default qemu graphical client you can use the remote-viewer from the virt-viewer package.  To connect pass the -spice port=5930,disable-ticketing flag to qemu.  See previous section for further information on how to do this.

Spice also allows you to do some nice stuff like share your clipboard with your VM.  To enable that you'll also have to pass the following flags to qemu:

     -device virtio-serial-pci,id=virtio-serial0,max_ports=16,bus=pci.0,addr=0x5
     -chardev spicevmc,name=vdagent,id=vdagent
     -device virtserialport,nr=1,bus=virtio-serial0.0,chardev=vdagent,
     name=com.redhat.spice.0

You'll also need to add the see Spice service.

Defining Services
-----------------

The previous sections show the available services and how one can combine them in an operating-system declaration.  But how do we define them in the first place?  And what is a service anyway?

Service Composition
...................

Here we define a service as, broadly, something that extends the functionality of the operating system.  Often a service is a process---a daemon---started when the system boots: a secure shell server, a Web server, the Guix build daemon, etc.  Sometimes a service is a daemon whose execution can be triggered by another daemon---e.g., an FTP server started by inetd or a D-Bus service activated by dbus-daemon.  Occasionally, a service does not map to a daemon.  For instance, the ``account'' service collects user accounts and makes sure they exist when the system runs; the ``udev'' service collects device management rules and makes them available to the eudev daemon; the /etc service populates the /etc directory of the system.

GuixSD services are connected by extensions.  For instance, the secure shell service extends the Shepherd---the GuixSD initialization system, running as PID 1---by giving it the command lines to start and stop the secure shell daemon (see lsh-service); the UPower service extends the D-Bus service by passing it its .service specification, and extends the udev service by passing it device management rules (see upower-service); the Guix daemon service extends the Shepherd by passing it the command lines to start and stop the daemon, and extends the account service by passing it a list of required build user accounts (see Base Services).

All in all, services and their ``extends'' relations form a directed acyclic graph (DAG).  If we represent services as boxes and extensions as arrows, a typical system might provide something like this:

Typical service extension graph.

At the bottom, we see the system service, which produces the directory containing everything to run and boot the system, as returned by the guix system build command.  See Service Reference, to learn about the other service types shown here. See the guix system extension-graph command, for information on how to generate this representation for a particular operating system definition.

Technically, developers can define service types to express these relations.  There can be any number of services of a given type on the system---for instance, a system running two instances of the GNU secure shell server (lsh) has two instances of LSH-SERVICE-TYPE, with different parameters.

The following section describes the programming interface for service types and services.

Service Types and Services
..........................

A service type is a node in the DAG described above.  Let us start with a simple example, the service type for the Guix build daemon (see Invoking guix-daemon):

     (define guix-service-type
       (service-type
        (name 'guix)
        (extensions
         (list (service-extension shepherd-root-service-type guix-shepherd-service)
               (service-extension account-service-type guix-accounts)
               (service-extension activation-service-type guix-activation)))))

It defines two things:

 1. A name, whose sole purpose is to make inspection and debugging easier.

 2. A list of service extensions, where each extension designates the target service type and a procedure that, given the parameters of the service, returns a list of objects to extend the service of that type.

     Every service type has at least one service extension.  The only exception is the boot service type, which is the ultimate service.

In this example, GUIX-SERVICE-TYPE extends three services:

shepherd-root-service-type
     The GUIX-SHEPHERD-SERVICE procedure defines how the Shepherd service is extended.  Namely, it returns a <shepherd-service> object that defines how guix-daemon is started and stopped (see Shepherd Services).

account-service-type
     This extension for this service is computed by GUIX-ACCOUNTS, which returns a list of user-group and user-account objects representing the build user accounts (see Invoking guix-daemon).

activation-service-type
     Here GUIX-ACTIVATION is a procedure that returns a gexp, which is a code snippet to run at ``activation time''---e.g., when the service is booted.

A service of this type is instantiated like this:

     (service guix-service-type
              (guix-configuration
                (build-accounts 5)
                (use-substitutes? #f)))

The second argument to the service form is a value representing the parameters of this specific service instance. See guix-configuration, for information about the guix-configuration data type.

GUIX-SERVICE-TYPE is quite simple because it extends other services but is not extensible itself.

The service type for an extensible service looks like this:

     (define udev-service-type
       (service-type (name 'udev)
                     (extensions
                      (list (service-extension shepherd-root-service-type
                                               udev-shepherd-service)))

                     (compose concatenate)       ;concatenate the list of rules
                     (extend (lambda (config rules)
                               (match config
                                 (($ <udev-configuration> udev initial-rules)
                                  (udev-configuration
                                   (udev udev)   ;the udev package to use
                                   (rules (append initial-rules rules)))))))))

This is the service type for the eudev device management daemon (https://wiki.gentoo.org/wiki/Project:Eudev).  Compared to the previous example, in addition to an extension of SHEPHERD-ROOT-SERVICE-TYPE, we see two new fields:

compose
     This is the procedure to compose the list of extensions to services of this type.

     Services can extend the udev service by passing it lists of rules; we compose those extensions simply by concatenating them.

extend
     This procedure defines how the value of the service is extended with the composition of the extensions.

     Udev extensions are composed into a list of rules, but the udev service value is itself a <udev-configuration> record.  So here, we extend that record by appending the list of rules it contains to the list of contributed rules.

There can be only one instance of an extensible service type such as UDEV-SERVICE-TYPE.  If there were more, the service-extension specifications would be ambiguous.

Still here?  The next section provides a reference of the programming interface for services.

Service Reference
.................

We have seen an overview of service types (see Service Types and Services).  This section provides a reference on how to manipulate services and service types.  This interface is provided by the (gnu services) module.

 -- Scheme Procedure: service TYPE VALUE
     Return a new service of TYPE, a <service-type> object (see below.)  VALUE can be any object; it represents the parameters of this particular service instance.

 -- Scheme Procedure: service? OBJ
     Return true if OBJ is a service.

 -- Scheme Procedure: service-kind SERVICE
     Return the type of SERVICE---i.e., a <service-type> object.

 -- Scheme Procedure: service-parameters SERVICE
     Return the value associated with SERVICE.  It represents its parameters.

Here is an example of how a service is created and manipulated:

     (define s
       (service nginx-service-type
                (nginx-configuration
                 (nginx nginx)
                 (log-directory log-directory)
                 (run-directory run-directory)
                 (file config-file))))

     (service? s)
     => #t

     (eq? (service-kind s) nginx-service-type)
     => #t

The modify-services form provides a handy way to change the parameters of some of the services of a list such as %BASE-SERVICES (see %base-services).  It evaluates to a list of services.  Of course, you could always use standard list combinators such as map and fold to do that (see List Library (GNU Guile Reference Manual)); modify-services simply provides a more concise form for this common pattern.

 -- Scheme Syntax: modify-services SERVICES
     (TYPE VARIABLE => BODY) ...

     Modify the services listed in SERVICES according to the given clauses.  Each clause has the form:

          (TYPE VARIABLE => BODY)

     where TYPE is a service type---e.g., guix-service-type---and VARIABLE is an identifier that is bound within the BODY to the service parameters---e.g., a guix-configuration instance---of the original service of that TYPE.

     The BODY should evaluate to the new service parameters, which will be used to configure the new service.  This new service will replace the original in the resulting list.  Because a service's service parameters are created using define-record-type*, you can write a succinct BODY that evaluates to the new service parameters by using the inherit feature that define-record-type* provides.

     See Using the Configuration System, for example usage.

Next comes the programming interface for service types.  This is something you want to know when writing new service definitions, but not necessarily when simply looking for ways to customize your operating-system declaration.

 -- Data Type: service-type
     This is the representation of a service type (see Service Types and Services).

     name
          This is a symbol, used only to simplify inspection and debugging.

     extensions
          A non-empty list of <service-extension> objects (see below).

     compose (default: #f)
          If this is #f, then the service type denotes services that cannot be extended---i.e., services that do not receive ``values'' from other services.

          Otherwise, it must be a one-argument procedure.  The procedure is called by fold-services and is passed a list of values collected from extensions.  It must return a value that is a valid parameter value for the service instance.

     extend (default: #f)
          If this is #f, services of this type cannot be extended.

          Otherwise, it must be a two-argument procedure: fold-services calls it, passing it the initial value of the service as the first argument and the result of applying compose to the extension values as the second argument.

     See Service Types and Services, for examples.

 -- Scheme Procedure: service-extension TARGET-TYPE
     COMPUTE
     Return a new extension for services of type TARGET-TYPE. COMPUTE must be a one-argument procedure: fold-services calls it, passing it the value associated with the service that provides the extension; it must return a valid value for the target service.

 -- Scheme Procedure: service-extension? OBJ
     Return true if OBJ is a service extension.

Occasionally, you might want to simply extend an existing service.  This involves creating a new service type and specifying the extension of interest, which can be verbose; the simple-service procedure provides a shorthand for this.

 -- Scheme Procedure: simple-service NAME TARGET VALUE
     Return a service that extends TARGET with VALUE.  This works by creating a singleton service type NAME, of which the returned service is an instance.

     For example, this extends mcron (see Scheduled Job Execution) with an additional job:

          (simple-service 'my-mcron-job mcron-service-type
                          #~(job '(next-hour (3)) "guix gc -F 2G"))

At the core of the service abstraction lies the fold-services procedure, which is responsible for ``compiling'' a list of services down to a single directory that contains everything needed to boot and run the system---the directory shown by the guix system build command (see Invoking guix system).  In essence, it propagates service extensions down the service graph, updating each node parameters on the way, until it reaches the root node.

 -- Scheme Procedure: fold-services SERVICES
     [#:target-type SYSTEM-SERVICE-TYPE]
     Fold SERVICES by propagating their extensions down to the root of type TARGET-TYPE; return the root service adjusted accordingly.

Lastly, the (gnu services) module also defines several essential service types, some of which are listed below.

 -- Scheme Variable: system-service-type
     This is the root of the service graph.  It produces the system directory as returned by the guix system build command.

 -- Scheme Variable: boot-service-type
     The type of the ``boot service'', which produces the boot script. The boot script is what the initial RAM disk runs when booting.

 -- Scheme Variable: etc-service-type
     The type of the /etc service.  This service can be extended by passing it name/file tuples such as:

          (list `("issue" ,(plain-file "issue" "Welcome!\n")))

     In this example, the effect would be to add an /etc/issue file pointing to the given file.

 -- Scheme Variable: setuid-program-service-type
     Type for the ``setuid-program service''.  This service collects lists of executable file names, passed as gexps, and adds them to the set of setuid-root programs on the system (see Setuid Programs).

 -- Scheme Variable: profile-service-type
     Type of the service that populates the system profile---i.e., the programs under /run/current-system/profile.  Other services can extend it by passing it lists of packages to add to the system profile.

Shepherd Services
.................

The (gnu services shepherd) module provides a way to define services managed by the GNU Shepherd, which is the GuixSD initialization system---the first process that is started when the system boots, also known as PID 1 (see Introduction (The GNU Shepherd Manual)).

Services in the Shepherd can depend on each other.  For instance, the SSH daemon may need to be started after the syslog daemon has been started, which in turn can only happen once all the file systems have been mounted.  The simple operating system defined earlier (see Using the Configuration System) results in a service graph like this:

Typical shepherd service graph.

You can actually generate such a graph for any operating system definition using the guix system shepherd-graph command (see guix system shepherd-graph).

The %SHEPHERD-ROOT-SERVICE is a service object representing PID 1, of type SHEPHERD-ROOT-SERVICE-TYPE; it can be extended by passing it lists of <shepherd-service> objects.

 -- Data Type: shepherd-service
     The data type representing a service managed by the Shepherd.

     provision
          This is a list of symbols denoting what the service provides.

          These are the names that may be passed to herd start, herd status, and similar commands (see Invoking herd (The GNU Shepherd Manual)).  See the provides slot (The GNU Shepherd Manual), for details.

     requirements (default: '())
          List of symbols denoting the Shepherd services this one depends on.

     respawn? (default: #t)
          Whether to restart the service when it stops, for instance when the underlying process dies.

     start
     stop (default: #~(const #f))
          The start and stop fields refer to the Shepherd's facilities to start and stop processes (see Service De- and Constructors (The GNU Shepherd Manual)).  They are given as G-expressions that get expanded in the Shepherd configuration file (see G-Expressions).

     documentation
          A documentation string, as shown when running:

               herd doc SERVICE-NAME

          where SERVICE-NAME is one of the symbols in PROVISION (see Invoking herd (The GNU Shepherd Manual)).

     modules (default: %DEFAULT-MODULES)
          This is the list of modules that must be in scope when start and stop are evaluated.

 -- Scheme Variable: shepherd-root-service-type
     The service type for the Shepherd ``root service''---i.e., PID 1.

     This is the service type that extensions target when they want to create shepherd services (see Service Types and Services, for an example). Each extension must pass a list of <shepherd-service>.

 -- Scheme Variable: %shepherd-root-service
     This service represents PID 1.

Installing Debugging Files
==========================

Program binaries, as produced by the GCC compilers for instance, are typically written in the ELF format, with a section containing debugging information.  Debugging information is what allows the debugger, GDB, to map binary code to source code; it is required to debug a compiled program in good conditions.

The problem with debugging information is that is takes up a fair amount of disk space.  For example, debugging information for the GNU C Library weighs in at more than 60 MiB.  Thus, as a user, keeping all the debugging info of all the installed programs is usually not an option. Yet, space savings should not come at the cost of an impediment to debugging---especially in the GNU system, which should make it easier for users to exert their computing freedom (see GNU Distribution).

Thankfully, the GNU Binary Utilities (Binutils) and GDB provide a mechanism that allows users to get the best of both worlds: debugging information can be stripped from the binaries and stored in separate files.  GDB is then able to load debugging information from those files, when they are available (see Separate Debug Files (Debugging with GDB)).

The GNU distribution takes advantage of this by storing debugging information in the lib/debug sub-directory of a separate package output unimaginatively called debug (see Packages with Multiple Outputs).  Users can choose to install the debug output of a package when they need it.  For instance, the following command installs the debugging information for the GNU C Library and for GNU Guile:

     guix package -i glibc:debug guile:debug

GDB must then be told to look for debug files in the user's profile, by setting the debug-file-directory variable (consider setting it from the ~/.gdbinit file, see Startup (Debugging with GDB)):

     (gdb) set debug-file-directory ~/.guix-profile/lib/debug

From there on, GDB will pick up debugging information from the .debug files under ~/.guix-profile/lib/debug.

In addition, you will most likely want GDB to be able to show the source code being debugged.  To do that, you will have to unpack the source code of the package of interest (obtained with guix build --source, see Invoking guix build), and to point GDB to that source directory using the directory command (see directory (Debugging with GDB)).

The debug output mechanism in Guix is implemented by the gnu-build-system (see Build Systems).  Currently, it is opt-in---debugging information is available only for the packages with definitions explicitly declaring a debug output.  This may be changed to opt-out in the future if our build farm servers can handle the load.  To check whether a package has a debug output, use guix package --list-available (see Invoking guix package).

Security Updates
================

Occasionally, important security vulnerabilities are discovered in software packages and must be patched.  Guix developers try hard to keep track of known vulnerabilities and to apply fixes as soon as possible in the master branch of Guix (we do not yet provide a ``stable'' branch containing only security updates.)  The guix lint tool helps developers find out about vulnerable versions of software packages in the distribution:

     $ guix lint -c cve
     gnu/packages/base.scm:652:2: glibc-2.21: probably vulnerable to CVE-2015-1781, CVE-2015-7547
     gnu/packages/gcc.scm:334:2: gcc-4.9.3: probably vulnerable to CVE-2015-5276
     gnu/packages/image.scm:312:2: openjpeg-2.1.0: probably vulnerable to CVE-2016-1923, CVE-2016-1924
     ...

See Invoking guix lint, for more information.

     As of version VERSION, the feature described below is considered ``beta''.

Guix follows a functional package management discipline (see Introduction), which implies that, when a package is changed, every package that depends on it must be rebuilt.  This can significantly slow down the deployment of fixes in core packages such as libc or Bash, since basically the whole distribution would need to be rebuilt.  Using pre-built binaries helps (see Substitutes), but deployment may still take more time than desired.

To address this, Guix implements grafts, a mechanism that allows for fast deployment of critical updates without the costs associated with a whole-distribution rebuild.  The idea is to rebuild only the package that needs to be patched, and then to ``graft'' it onto packages explicitly installed by the user and that were previously referring to the original package.  The cost of grafting is typically very low, and order of magnitudes lower than a full rebuild of the dependency chain.

For instance, suppose a security update needs to be applied to Bash. Guix developers will provide a package definition for the ``fixed'' Bash, say BASH-FIXED, in the usual way (see Defining Packages).  Then, the original package definition is augmented with a replacement field pointing to the package containing the bug fix:

     (define bash
       (package
         (name "bash")
         ;; ...
         (replacement bash-fixed)))

From there on, any package depending directly or indirectly on Bash---as reported by guix gc --requisites (see Invoking guix gc)---that is installed is automatically ``rewritten'' to refer to BASH-FIXED instead of BASH.  This grafting process takes time proportional to the size of the package, usually less than a minute for an ``average'' package on a recent machine.  Grafting is recursive: when an indirect dependency requires grafting, then grafting ``propagates'' up to the package that the user is installing.

Currently, the length of the name and version of the graft and that of the package it replaces (BASH-FIXED and BASH in the example above) must be equal.  This restriction mostly comes from the fact that grafting works by patching files, including binary files, directly. Other restrictions may apply: for instance, when adding a graft to a package providing a shared library, the original shared library and its replacement must have the same SONAME and be binary-compatible.

The --no-grafts command-line option allows you to forcefully avoid grafting (see --no-grafts). Thus, the command:

     guix build bash --no-grafts

returns the store file name of the original Bash, whereas:

     guix build bash

returns the store file name of the ``fixed'', replacement Bash.  This allows you to distinguish between the two variants of Bash.

To verify which Bash your whole profile refers to, you can run (see Invoking guix gc):

     guix gc -R `readlink -f ~/.guix-profile` | grep bash

... and compare the store file names that you get with those above. Likewise for a complete GuixSD system generation:

     guix gc -R `guix system build my-config.scm` | grep bash

Lastly, to check which Bash running processes are using, you can use the lsof command:

     lsof | grep /gnu/store/.*bash

Package Modules
===============

From a programming viewpoint, the package definitions of the GNU distribution are provided by Guile modules in the (gnu packages ...) name space (Note that packages under the (gnu packages ...) module name space are not necessarily ``GNU packages''.  This module naming scheme follows the usual Guile module naming convention: gnu means that these modules are distributed as part of the GNU system, and packages identifies modules that define packages.)  (see Guile modules (GNU Guile Reference Manual)).  For instance, the (gnu packages emacs) module exports a variable named emacs, which is bound to a <package> object (see Defining Packages).

The (gnu packages ...) module name space is automatically scanned for packages by the command-line tools.  For instance, when running guix package -i emacs, all the (gnu packages ...) modules are scanned until one that exports a package object whose name is emacs is found.  This package search facility is implemented in the (gnu packages) module.

Users can store package definitions in modules with different names---e.g., (my-packages emacs) (Note that the file name and module name must match.  For instance, the (my-packages emacs) module must be stored in a my-packages/emacs.scm file relative to the load path specified with --load-path or GUIX_PACKAGE_PATH.  See Modules and the File System (GNU Guile Reference Manual), for details.).  These package definitions will not be visible by default.  Users can invoke commands such as guix package and guix build with the -e option so that they know where to find the package.  Better yet, they can use the -L option of these commands to make those modules visible (see --load-path), or define the GUIX_PACKAGE_PATH environment variable.  This environment variable makes it easy to extend or customize the distribution and is honored by all the user interfaces.

 -- Environment Variable: GUIX_PACKAGE_PATH
     This is a colon-separated list of directories to search for additional package modules.  Directories listed in this variable take precedence over the own modules of the distribution.

The distribution is fully bootstrapped and self-contained: each package is built based solely on other packages in the distribution.  The root of this dependency graph is a small set of bootstrap binaries, provided by the (gnu packages bootstrap) module.  For more information on bootstrapping, see Bootstrapping.

Packaging Guidelines
====================

The GNU distribution is nascent and may well lack some of your favorite packages.  This section describes how you can help make the distribution grow.  See Contributing, for additional information on how you can help.

Free software packages are usually distributed in the form of source code tarballs---typically tar.gz files that contain all the source files.  Adding a package to the distribution means essentially two things: adding a recipe that describes how to build the package, including a list of other packages required to build it, and adding package metadata along with that recipe, such as a description and licensing information.

In Guix all this information is embodied in package definitions. Package definitions provide a high-level view of the package.  They are written using the syntax of the Scheme programming language; in fact, for each package we define a variable bound to the package definition, and export that variable from a module (see Package Modules). However, in-depth Scheme knowledge is not a prerequisite for creating packages.  For more information on package definitions, see Defining Packages.

Once a package definition is in place, stored in a file in the Guix source tree, it can be tested using the guix build command (see Invoking guix build).  For example, assuming the new package is called gnew, you may run this command from the Guix build tree (see Running Guix Before It Is Installed):

     ./pre-inst-env guix build gnew --keep-failed

Using --keep-failed makes it easier to debug build failures since it provides access to the failed build tree.  Another useful command-line option when debugging is --log-file, to access the build log.

If the package is unknown to the guix command, it may be that the source file contains a syntax error, or lacks a define-public clause to export the package variable.  To figure it out, you may load the module from Guile to get more information about the actual error:

     ./pre-inst-env guile -c '(use-modules (gnu packages gnew))'

Once your package builds correctly, please send us a patch (see Contributing).  Well, if you need help, we will be happy to help you too.  Once the patch is committed in the Guix repository, the new package automatically gets built on the supported platforms by our continuous integration system (http://hydra.gnu.org/jobset/gnu/master).

Users can obtain the new package definition simply by running guix pull (see Invoking guix pull).  When hydra.gnu.org is done building the package, installing the package automatically downloads binaries from there (see Substitutes).  The only place where human intervention is needed is to review and apply the patch.

Software Freedom
----------------

The GNU operating system has been developed so that users can have freedom in their computing.  GNU is free software, meaning that users have the four essential freedoms (http://www.gnu.org/philosophy/free-sw.html): to run the program, to study and change the program in source code form, to redistribute exact copies, and to distribute modified versions.  Packages found in the GNU distribution provide only software that conveys these four freedoms.

In addition, the GNU distribution follow the free software distribution guidelines (http://www.gnu.org/distros/free-system-distribution-guidelines.html).  Among other things, these guidelines reject non-free firmware, recommendations of non-free software, and discuss ways to deal with trademarks and patents.

Some otherwise free upstream package sources contain a small and optional subset that violates the above guidelines, for instance because this subset is itself non-free code.  When that happens, the offending items are removed with appropriate patches or code snippets in the origin form of the package (see Defining Packages).  This way, guix build --source returns the ``freed'' source rather than the unmodified upstream source.

Package Naming
--------------

A package has actually two names associated with it: First, there is the name of the Scheme variable, the one following define-public.  By this name, the package can be made known in the Scheme code, for instance as input to another package.  Second, there is the string in the name field of a package definition.  This name is used by package management commands such as guix package and guix build.

Both are usually the same and correspond to the lowercase conversion of the project name chosen upstream, with underscores replaced with hyphens.  For instance, GNUnet is available as gnunet, and SDL_net as sdl-net.

We do not add lib prefixes for library packages, unless these are already part of the official project name.  But see Python Modules and Perl Modules for special rules concerning modules for the Python and Perl languages.

Font package names are handled differently, see Fonts.

Version Numbers
---------------

We usually package only the latest version of a given free software project.  But sometimes, for instance for incompatible library versions, two (or more) versions of the same package are needed.  These require different Scheme variable names.  We use the name as defined in Package Naming for the most recent version; previous versions use the same name, suffixed by - and the smallest prefix of the version number that may distinguish the two versions.

The name inside the package definition is the same for all versions of a package and does not contain any version number.

For instance, the versions 2.24.20 and 3.9.12 of GTK+ may be packaged as follows:

     (define-public gtk+
       (package
         (name "gtk+")
         (version "3.9.12")
         ...))
     (define-public gtk+-2
       (package
         (name "gtk+")
         (version "2.24.20")
         ...))

If we also wanted GTK+ 3.8.2, this would be packaged as

     (define-public gtk+-3.8
       (package
         (name "gtk+")
         (version "3.8.2")
         ...))

Occasionally, we package snapshots of upstream's version control system (VCS) instead of formal releases.  This should remain exceptional, because it is up to upstream developers to clarify what the stable release is.  Yet, it is sometimes necessary.  So, what should we put in the version field?

Clearly, we need to make the commit identifier of the VCS snapshot visible in the version string, but we also need to make sure that the version string is monotonically increasing so that guix package --upgrade can determine which version is newer.  Since commit identifiers, notably with Git, are not monotonically increasing, we add a revision number that we increase each time we upgrade to a newer snapshot.  The resulting version string looks like this:

     2.0.11-3.cabba9e
       ^    ^    ^
       |    |    `-- upstream commit ID
       |    |
       |    `--- Guix package revision
       |
     latest upstream version

It is a good idea to strip commit identifiers in the version field to, say, 7 digits.  It avoids an aesthetic annoyance (assuming aesthetics have a role to play here) as well as problems related to OS limits such as the maximum shebang length (127 bytes for the Linux kernel.)  It is best to use the full commit identifiers in origins, though, to avoid ambiguities.  A typical package definition may look like this:

     (define my-package
       (let ((commit "c3f29bc928d5900971f65965feaae59e1272a3f7")
             (revision "1"))          ;Guix package revision
         (package
           (version (string-append "0.9-" revision "."
                                   (string-take commit 7)))
           (source (origin
                     (method git-fetch)
                     (uri (git-reference
                           (url "git://example.org/my-package.git")
                           (commit commit)))
                     (sha256 (base32 "1mbikn..."))
                     (file-name (string-append "my-package-" version
                                               "-checkout"))))
           ;; ...
           )))

Synopses and Descriptions
-------------------------

As we have seen before, each package in GNU Guix includes a synopsis and a description (see Defining Packages).  Synopses and descriptions are important: They are what guix package --search searches, and a crucial piece of information to help users determine whether a given package suits their needs.  Consequently, packagers should pay attention to what goes into them.

Synopses must start with a capital letter and must not end with a period.  They must not start with ``a'' or ``the'', which usually does not bring anything; for instance, prefer ``File-frobbing tool'' over ``A tool that frobs files''.  The synopsis should say what the package is---e.g., ``Core GNU utilities (file, text, shell)''---or what it is used for---e.g., the synopsis for GNU grep is ``Print lines matching a pattern''.

Keep in mind that the synopsis must be meaningful for a very wide audience.  For example, ``Manipulate alignments in the SAM format'' might make sense for a seasoned bioinformatics researcher, but might be fairly unhelpful or even misleading to a non-specialized audience.  It is a good idea to come up with a synopsis that gives an idea of the application domain of the package.  In this example, this might give something like ``Manipulate nucleotide sequence alignments'', which hopefully gives the user a better idea of whether this is what they are looking for.

Descriptions should take between five and ten lines.  Use full sentences, and avoid using acronyms without first introducing them. Please avoid marketing phrases such as ``world-leading'', ``industrial-strength'', and ``next-generation'', and avoid superlatives like ``the most advanced''---they are not helpful to users looking for a package and may even sound suspicious.  Instead, try to be factual, mentioning use cases and features.

Descriptions can include Texinfo markup, which is useful to introduce ornaments such as @code or @dfn, bullet lists, or hyperlinks (see Overview (GNU Texinfo)).  However you should be careful when using some characters for example @ and curly braces which are the basic special characters in Texinfo (see Special Characters (GNU Texinfo)).  User interfaces such as guix package --show take care of rendering it appropriately.

Synopses and descriptions are translated by volunteers at the Translation Project (http://translationproject.org/domain/guix-packages.html) so that as many users as possible can read them in their native language.  User interfaces search them and display them in the language specified by the current locale.

Translation is a lot of work so, as a packager, please pay even more attention to your synopses and descriptions as every change may entail additional work for translators.  In order to help them, it is possible to make recommendations or instructions visible to them by inserting special comments like this (see xgettext Invocation (GNU Gettext)):

     ;; TRANSLATORS: "X11 resize-and-rotate" should not be translated.
     (description "ARandR is designed to provide a simple visual front end
     for the X11 resize-and-rotate (RandR) extension. ...")

Python Modules
--------------

We currently package Python 2 and Python 3, under the Scheme variable names python-2 and python as explained in Version Numbers. To avoid confusion and naming clashes with other programming languages, it seems desirable that the name of a package for a Python module contains the word python.

Some modules are compatible with only one version of Python, others with both. If the package Foo compiles only with Python 3, we name it python-foo; if it compiles only with Python 2, we name it python2-foo. If it is compatible with both versions, we create two packages with the corresponding names.

If a project already contains the word python, we drop this; for instance, the module python-dateutil is packaged under the names python-dateutil and python2-dateutil.  If the project name starts with py (e.g. pytz), we keep it and prefix it as described above.

Specifying Dependencies
.......................

Dependency information for Python packages is usually available in the package source tree, with varying degrees of accuracy: in the setup.py file, in requirements.txt, or in tox.ini.

Your mission, when writing a recipe for a Python package, is to map these dependencies to the appropriate type of ``input'' (see inputs).  Although the pypi importer normally does a good job (see Invoking guix import), you may want to check the following check list to determine which dependency goes where.

  * We currently package Python 2 with setuptools and pip installed like Python 3.4 has per default.  Thus you don't need to specify either of these as an input.  guix lint will warn you if you do.

  * Python dependencies required at run time go into propagated-inputs.  They are typically defined with the install_requires keyword in setup.py, or in the requirements.txt file.

  * Python packages required only at build time---e.g., those listed with the setup_requires keyword in setup.py---or only for testing---e.g., those in tests_require---go into native-inputs.  The rationale is that (1) they do not need to be propagated because they are not needed at run time, and (2) in a cross-compilation context, it's the ``native'' input that we'd want.

     Examples are the pytest, mock, and nose test frameworks.  Of course if any of these packages is also required at run-time, it needs to go to propagated-inputs.

  * Anything that does not fall in the previous categories goes to inputs, for example programs or C libraries required for building Python packages containing C extensions.

  * If a Python package has optional dependencies (extras_require), it is up to you to decide whether to add them or not, based on their usefulness/overhead ratio (see guix size).

Perl Modules
------------

Perl programs standing for themselves are named as any other package, using the lowercase upstream name. For Perl packages containing a single class, we use the lowercase class name, replace all occurrences of :: by dashes and prepend the prefix perl-. So the class XML::Parser becomes perl-xml-parser. Modules containing several classes keep their lowercase upstream name and are also prepended by perl-.  Such modules tend to have the word perl somewhere in their name, which gets dropped in favor of the prefix.  For instance, libwww-perl becomes perl-libwww.

Java Packages
-------------

Java programs standing for themselves are named as any other package, using the lowercase upstream name.

To avoid confusion and naming clashes with other programming languages, it is desirable that the name of a package for a Java package is prefixed with java-.  If a project already contains the word java, we drop this; for instance, the package ngsjava is packaged under the name java-ngs.

For Java packages containing a single class or a small class hierarchy, we use the lowercase class name, replace all occurrences of . by dashes and prepend the prefix java-.  So the class apache.commons.cli becomes package java-apache-commons-cli.

Fonts
-----

For fonts that are in general not installed by a user for typesetting purposes, or that are distributed as part of a larger software package, we rely on the general packaging rules for software; for instance, this applies to the fonts delivered as part of the X.Org system or fonts that are part of TeX Live.

To make it easier for a user to search for fonts, names for other packages containing only fonts are constructed as follows, independently of the upstream package name.

The name of a package containing only one font family starts with font-; it is followed by the foundry name and a dash - if the foundry is known, and the font family name, in which spaces are replaced by dashes (and as usual, all upper case letters are transformed to lower case). For example, the Gentium font family by SIL is packaged under the name font-sil-gentium.

For a package containing several font families, the name of the collection is used in the place of the font family name. For instance, the Liberation fonts consist of three families, Liberation Sans, Liberation Serif and Liberation Mono. These could be packaged separately under the names font-liberation-sans and so on; but as they are distributed together under a common name, we prefer to package them together as font-liberation.

In the case where several formats of the same font family or font collection are packaged separately, a short form of the format, prepended by a dash, is added to the package name.  We use -ttf for TrueType fonts, -otf for OpenType fonts and -type1 for PostScript Type 1 fonts.

Bootstrapping
=============

Bootstrapping in our context refers to how the distribution gets built ``from nothing''.  Remember that the build environment of a derivation contains nothing but its declared inputs (see Introduction).  So there's an obvious chicken-and-egg problem: how does the first package get built?  How does the first compiler get compiled?  Note that this is a question of interest only to the curious hacker, not to the regular user, so you can shamelessly skip this section if you consider yourself a ``regular user''.

The GNU system is primarily made of C code, with libc at its core.  The GNU build system itself assumes the availability of a Bourne shell and command-line tools provided by GNU Coreutils, Awk, Findutils, `sed', and `grep'.  Furthermore, build programs---programs that run ./configure, make, etc.---are written in Guile Scheme (see Derivations).  Consequently, to be able to build anything at all, from scratch, Guix relies on pre-built binaries of Guile, GCC, Binutils, libc, and the other packages mentioned above---the bootstrap binaries.

These bootstrap binaries are ``taken for granted'', though we can also re-create them if needed (more on that later).

Preparing to Use the Bootstrap Binaries
---------------------------------------

Dependency graph of the early bootstrap derivations

The figure above shows the very beginning of the dependency graph of the distribution, corresponding to the package definitions of the (gnu packages bootstrap) module.  A similar figure can be generated with guix graph (see Invoking guix graph), along the lines of:

     guix graph -t derivation \
       -e '(@@ (gnu packages bootstrap) %bootstrap-gcc)' \
       | dot -Tps > t.ps

At this level of detail, things are slightly complex.  First, Guile itself consists of an ELF executable, along with many source and compiled Scheme files that are dynamically loaded when it runs.  This gets stored in the guile-2.0.7.tar.xz tarball shown in this graph.  This tarball is part of Guix's ``source'' distribution, and gets inserted into the store with add-to-store (see The Store).

But how do we write a derivation that unpacks this tarball and adds it to the store?  To solve this problem, the guile-bootstrap-2.0.drv derivation---the first one that gets built---uses bash as its builder, which runs build-bootstrap-guile.sh, which in turn calls tar to unpack the tarball.  Thus, bash, tar, xz, and mkdir are statically-linked binaries, also part of the Guix source distribution, whose sole purpose is to allow the Guile tarball to be unpacked.

Once guile-bootstrap-2.0.drv is built, we have a functioning Guile that can be used to run subsequent build programs.  Its first task is to download tarballs containing the other pre-built binaries---this is what the .tar.xz.drv derivations do.  Guix modules such as ftp-client.scm are used for this purpose.  The module-import.drv derivations import those modules in a directory in the store, using the original layout.  The module-import-compiled.drv derivations compile those modules, and write them in an output directory with the right layout.  This corresponds to the #:modules argument of build-expression->derivation (see Derivations).

Finally, the various tarballs are unpacked by the derivations gcc-bootstrap-0.drv, glibc-bootstrap-0.drv, etc., at which point we have a working C tool chain.

Building the Build Tools
------------------------

Bootstrapping is complete when we have a full tool chain that does not depend on the pre-built bootstrap tools discussed above.  This no-dependency requirement is verified by checking whether the files of the final tool chain contain references to the /gnu/store directories of the bootstrap inputs.  The process that leads to this ``final'' tool chain is described by the package definitions found in the (gnu packages commencement) module.

The guix graph command allows us to ``zoom out'' compared to the graph above, by looking at the level of package objects instead of individual derivations---remember that a package may translate to several derivations, typically one derivation to download its source, one to build the Guile modules it needs, and one to actually build the package from source.  The command:

     guix graph -t bag \
       -e '(@@ (gnu packages commencement)
               glibc-final-with-bootstrap-bash)' | dot -Tps > t.ps

produces the dependency graph leading to the ``final'' C library (You may notice the glibc-intermediate label, suggesting that it is not quite final, but as a good approximation, we will consider it final.), depicted below.

Dependency graph of the early packages

The first tool that gets built with the bootstrap binaries is GNU Make---noted make-boot0 above---which is a prerequisite for all the following packages.  From there Findutils and Diffutils get built.

Then come the first-stage Binutils and GCC, built as pseudo cross tools---i.e., with --target equal to --host.  They are used to build libc.  Thanks to this cross-build trick, this libc is guaranteed not to hold any reference to the initial tool chain.

From there the final Binutils and GCC (not shown above) are built. GCC uses ld from the final Binutils, and links programs against the just-built libc. This tool chain is used to build the other packages used by Guix and by the GNU Build System: Guile, Bash, Coreutils, etc.

And voilà!  At this point we have the complete set of build tools that the GNU Build System expects.  These are in the %final-inputs variable of the (gnu packages commencement) module, and are implicitly used by any package that uses gnu-build-system (see gnu-build-system).

Building the Bootstrap Binaries
-------------------------------

Because the final tool chain does not depend on the bootstrap binaries, those rarely need to be updated.  Nevertheless, it is useful to have an automated way to produce them, should an update occur, and this is what the (gnu packages make-bootstrap) module provides.

The following command builds the tarballs containing the bootstrap binaries (Guile, Binutils, GCC, libc, and a tarball containing a mixture of Coreutils and other basic command-line tools):

     guix build bootstrap-tarballs

The generated tarballs are those that should be referred to in the (gnu packages bootstrap) module mentioned at the beginning of this section.

Still here?  Then perhaps by now you've started to wonder: when do we reach a fixed point?  That is an interesting question!  The answer is unknown, but if you would like to investigate further (and have significant computational and storage resources to do so), then let us know.

Porting to a New Platform
=========================

As discussed above, the GNU distribution is self-contained, and self-containment is achieved by relying on pre-built ``bootstrap binaries'' (see Bootstrapping).  These binaries are specific to an operating system kernel, CPU architecture, and application binary interface (ABI).  Thus, to port the distribution to a platform that is not yet supported, one must build those bootstrap binaries, and update the (gnu packages bootstrap) module to use them on that platform.

Fortunately, Guix can cross compile those bootstrap binaries. When everything goes well, and assuming the GNU tool chain supports the target platform, this can be as simple as running a command like this one:

     guix build --target=armv5tel-linux-gnueabi bootstrap-tarballs

For this to work, the glibc-dynamic-linker procedure in (gnu packages bootstrap) must be augmented to return the right file name for libc's dynamic linker on that platform; likewise, system->linux-architecture in (gnu packages linux) must be taught about the new platform.

Once these are built, the (gnu packages bootstrap) module needs to be updated to refer to these binaries on the target platform.  That is, the hashes and URLs of the bootstrap tarballs for the new platform must be added alongside those of the currently supported platforms.  The bootstrap Guile tarball is treated specially: it is expected to be available locally, and gnu/local.mk has rules do download it for the supported architectures; a rule for the new platform must be added as well.

In practice, there may be some complications.  First, it may be that the extended GNU triplet that specifies an ABI (like the eabi suffix above) is not recognized by all the GNU tools.  Typically, glibc recognizes some of these, whereas GCC uses an extra --with-abi configure flag (see gcc.scm for examples of how to handle this). Second, some of the required packages could fail to build for that platform.  Lastly, the generated binaries could be broken for some reason.

     [file contributing.texi not included]

Acknowledgments
***************

Guix is based on the Nix package manager (http://nixos.org/nix/), which was designed and implemented by Eelco Dolstra, with contributions from other people (see the nix/AUTHORS file in Guix.)  Nix pioneered functional package management, and promoted unprecedented features, such as transactional package upgrades and rollbacks, per-user profiles, and referentially transparent build processes.  Without this work, Guix would not exist.

The Nix-based software distributions, Nixpkgs and NixOS, have also been an inspiration for Guix.

GNU Guix itself is a collective work with contributions from a number of people.  See the AUTHORS file in Guix for more information on these fine people.  The THANKS file lists people who have helped by reporting bugs, taking care of the infrastructure, providing artwork and themes, making suggestions, and more---thank you!

GNU Free Documentation License
******************************

     [file fdl-1.3.texi not included]