| | 1 | <?xml version="1.0"?> |
| | 2 | <html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/><title>lockmail</title><link rel="stylesheet" href="style.css" type="text/css"/><meta name="generator" content="DocBook XSL Stylesheets V1.72.0"/><link rel="start" href="#lockmail" title="lockmail"/><link xmlns="" rel="stylesheet" type="text/css" href="manpage.css"/><meta xmlns="" name="MSSmartTagsPreventParsing" content="TRUE"/><link xmlns="" rel="icon" href="icon.gif" type="image/gif"/><!-- |
| | 3 | |
| | 4 | Copyright 1998 - 2007 Double Precision, Inc. See COPYING for distribution |
| | 5 | information. |
| | 6 | |
| | 7 | --></head><body><div class="refentry" lang="en" xml:lang="en"><a id="lockmail" shape="rect"> </a><div class="titlepage"/><div class="refnamediv"><h2>Name</h2><p>lockmail — create mail lock files</p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><div class="cmdsynopsis"><p><code class="command">lockmail</code> [-r] [-t <em class="replaceable"><code>timeout</code></em>] {<em class="replaceable"><code>lockfile</code></em>} {<em class="replaceable"><code>program</code></em>} [argument...]</p></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="id282326" shape="rect"> </a><h2>DESCRIPTION</h2><p> |
| | 8 | <span><strong class="command">lockmail</strong></span> is a helper utility for working with mailbox |
| | 9 | files. |
| | 10 | Mailbox files must be locked to prevent other applications from modifying the |
| | 11 | mailbox at the same time. |
| | 12 | Different system use different locking conventions. |
| | 13 | <span><strong class="command">lockmail</strong></span> uses two of the most common locking mechanisms |
| | 14 | in use, which should work reliably on most systems.</p><p> |
| | 15 | <em class="replaceable"><code>lockfile</code></em> is the pathname to an existing mailbox |
| | 16 | file. |
| | 17 | By default, <span><strong class="command">lockmail</strong></span> tries to lock the mailbox every |
| | 18 | five seconds (if the mailbox is already locked), and will give up after |
| | 19 | three minutes. |
| | 20 | After the mailbox is succesfully locked, <span><strong class="command">lockmail</strong></span> runs |
| | 21 | <em class="replaceable"><code>program</code></em> as a child process, with any optional |
| | 22 | <em class="replaceable"><code>argument</code></em>s. |
| | 23 | When <em class="replaceable"><code>program</code></em> terminates, <span><strong class="command">lockmail</strong></span> |
| | 24 | removes the mailbox lock, and terminates itself.</p></div><div class="refsect1" lang="en" xml:lang="en"><a id="id282387" shape="rect"> </a><h2>OPTIONS</h2><div class="variablelist"><dl><dt><span class="term">-r</span></dt><dd><p> |
| | 25 | If a regular lock fails, try a read-only lock. |
| | 26 | Use this option to lock mailbox files in a read-only directory.</p></dd><dt><span class="term">-t <em class="replaceable"><code>timeout</code></em></span></dt><dd><p> |
| | 27 | If the lock attempt fails, try again for up to |
| | 28 | <em class="replaceable"><code>timeout</code></em> seconds. |
| | 29 | The actual timeout is rounded up to the next five second interval |
| | 30 | (a lock attempt is tried every five seconds).</p></dd></dl></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="id282626" shape="rect"> </a><h2>DESCRIPTION</h2><p> |
| | 31 | This section briefly describes the locking mechanism used by |
| | 32 | <span><strong class="command">lockmail</strong></span>. |
| | 33 | <span><strong class="command">lockmail</strong></span> uses three different locking conventions in |
| | 34 | order to maximize compatibility with other mail software: |
| | 35 | C-Client folder locks, dot-locks, and file locks. |
| | 36 | </p><div class="refsect2" lang="en" xml:lang="en"><a id="id282648" shape="rect"> </a><h3>C-Client folder locks</h3><p> |
| | 37 | Mail software based on the <code class="literal">C-Client</code> library creates |
| | 38 | lock files named |
| | 39 | <code class="filename">/tmp/.<em class="replaceable"><code>dddddd</code></em>.<em class="replaceable"><code>iiiiii</code></em></code>. |
| | 40 | Here, <em class="replaceable"><code>dddddd</code></em> and <em class="replaceable"><code>iiiiii</code></em> |
| | 41 | are the device number and the inode number of the mailbox file |
| | 42 | (the <em class="structfield"><code>st_dev</code></em> and <em class="structfield"><code>st_ino</code></em> |
| | 43 | fields in the inode), in hexadecimal. |
| | 44 | If the process ID saved in the C-Client folder lock file is not valid, |
| | 45 | <span><strong class="command">lockmail</strong></span> concludes that it's a stale lock file, and |
| | 46 | will remove it.</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p> |
| | 47 | A race condition exists where a <code class="literal">C-Client</code> process is |
| | 48 | killed after it creates a lock file, but before saving its process ID in the |
| | 49 | lock file. |
| | 50 | The race window is very small, but it exists. |
| | 51 | The <code class="literal">C-Client</code> library does not appear to ever clear out |
| | 52 | the lock file.</p><p> |
| | 53 | <span><strong class="command">lockmail</strong></span> |
| | 54 | attempts to resolve this race condition by deleting zero-length lock files |
| | 55 | that are at least five minutes old.</p></div></div><div class="refsect2" lang="en" xml:lang="en"><a id="id281884" shape="rect"> </a><h3>dot-locks</h3><p> |
| | 56 | <span><strong class="command">lockmail</strong></span> |
| | 57 | also creates, and honors dot-lock files. |
| | 58 | Dot-lock files are first created as temporary files, then linked to |
| | 59 | <code class="filename"><em class="replaceable"><code>lockfile</code></em>.lock</code>. |
| | 60 | The link operation fails if the dot-lock file already exists. |
| | 61 | <span><strong class="command">lockmail</strong></span> |
| | 62 | uses an enhanced method of dot-locking, where its process ID, and the name |
| | 63 | of the server where <span><strong class="command">lockmail</strong></span> is running is also saved |
| | 64 | in its dot-lock file. |
| | 65 | If the operation fails due to an existing dot-lock file that was created |
| | 66 | by another <span><strong class="command">lockmail</strong></span> process on the same server, and the |
| | 67 | process ID no longer exists, this stale dot-lock file is removed immediately. |
| | 68 | In all other situations a dot-lock file older than five minutes is considered |
| | 69 | stale, and removed. |
| | 70 | </p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p> |
| | 71 | A failure to create a dot-lock file is silently ignored if the reason for |
| | 72 | the failure is because |
| | 73 | <span><strong class="command">lockmail</strong></span> |
| | 74 | does not have the write permission in the dot-lock file's directory. |
| | 75 | The incoming mail spool directory (usually |
| | 76 | <code class="filename">/var/mail</code>) |
| | 77 | typically does not have global write permissions, so the attempt to |
| | 78 | create the dot-lock file in the spool directory will fail, and |
| | 79 | <span><strong class="command">lockmail</strong></span> |
| | 80 | will be content with using file-locking only. |
| | 81 | </p></div></div><div class="refsect2" lang="en" xml:lang="en"><a id="id281958" shape="rect"> </a><h3>File locks</h3><p> |
| | 82 | The final locking mechanism |
| | 83 | <span><strong class="command">lockmail</strong></span> |
| | 84 | uses is the operating system's file locking facility. |
| | 85 | If |
| | 86 | <span><strong class="command">lockmail</strong></span> |
| | 87 | fails to obtain all three locks, |
| | 88 | <span><strong class="command">lockmail</strong></span> |
| | 89 | will sleep for five seconds and try again. |
| | 90 | The only exception is a failure to create a dot-lock because of no write |
| | 91 | access to the dot-lock file's directory, which is ignored. |
| | 92 | If |
| | 93 | <span><strong class="command">lockmail</strong></span> |
| | 94 | still fails to obtain all required locks in the amount of time specified |
| | 95 | by the <code class="option">-t</code> option (or its default value), |
| | 96 | <span><strong class="command">lockmail</strong></span> will terminate with the |
| | 97 | <code class="literal">EX_TEMPFAIL</code> exit code. |
| | 98 | </p><p> |
| | 99 | <span><strong class="command">lockmail</strong></span> |
| | 100 | runs <em class="replaceable"><code>program</code></em> after obtaining the last file |
| | 101 | lock, waits until <em class="replaceable"><code>program</code></em> terminates, and |
| | 102 | releases all locks. |
| | 103 | <em class="replaceable"><code>program</code></em> must terminate before any of the locks |
| | 104 | obtained by <span><strong class="command">lockmail</strong></span> expire, and are considered stale. |
| | 105 | <span><strong class="command">lockmail</strong></span> will then terminate with the same exit code |
| | 106 | as <em class="replaceable"><code>program</code></em>.</p></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="id325274" shape="rect"> </a><h2>EXIT STATUS</h2><p> |
| | 107 | <span><strong class="command">lockmail</strong></span> terminates with the same exit status as |
| | 108 | <em class="replaceable"><code>program</code></em> |
| | 109 | <span><strong class="command">lockmail</strong></span> terminates with the <code class="literal">EX_TEMPFAIL</code> |
| | 110 | exit status if it was unable to obtain a lock, or if |
| | 111 | <em class="replaceable"><code>program</code></em> |
| | 112 | was killed by a signal.</p></div><div class="refsect1" lang="en" xml:lang="en"><a id="id325310" shape="rect"> </a><h2>SEE ALSO</h2><p> |
| | 113 | <a href="maildrop.html" target="_top" shape="rect"><span class="citerefentry"><span class="refentrytitle">maildrop</span>(1)</span></a>, |
| | 114 | <span class="citerefentry"><span class="refentrytitle">sendmail</span>(8)</span>. |
| | 115 | </p></div></div></body></html> |
HCoop / hcoop / debian / courier-authlib.git / blame_incremental