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-
-Copyright 1998 - 2007 Double Precision, Inc. See COPYING for distribution
-information.
-
---></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="id401215" shape="rect"> </a><h2>DESCRIPTION</h2><p>
-<span class="command"><strong>lockmail</strong></span> is a helper utility for working with mailbox
-files.
-Mailbox files must be locked to prevent other applications from modifying the
-mailbox at the same time.
-Different system use different locking conventions.
-<span class="command"><strong>lockmail</strong></span> uses two of the most common locking mechanisms
-in use, which should work reliably on most systems.</p><p>
-<em class="replaceable"><code>lockfile</code></em> is the pathname to an existing mailbox
-file.
-By default, <span class="command"><strong>lockmail</strong></span> tries to lock the mailbox every
-five seconds (if the mailbox is already locked), and will give up after
-three minutes.
-After the mailbox is succesfully locked, <span class="command"><strong>lockmail</strong></span> runs
-<em class="replaceable"><code>program</code></em> as a child process, with any optional
-<em class="replaceable"><code>argument</code></em>s.
-When <em class="replaceable"><code>program</code></em> terminates, <span class="command"><strong>lockmail</strong></span>
-removes the mailbox lock, and terminates itself.</p></div><div class="refsect1" lang="en" xml:lang="en"><a id="id366992" shape="rect"> </a><h2>OPTIONS</h2><div class="variablelist"><dl><dt><span class="term">-r</span></dt><dd><p>
-If a regular lock fails, try a read-only lock.
-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>
-If the lock attempt fails, try again for up to
-<em class="replaceable"><code>timeout</code></em> seconds.
-The actual timeout is rounded up to the next five second interval
-(a lock attempt is tried every five seconds).</p></dd></dl></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="id366015" shape="rect"> </a><h2>DESCRIPTION</h2><p>
-This section briefly describes the locking mechanism used by
-<span class="command"><strong>lockmail</strong></span>.
-<span class="command"><strong>lockmail</strong></span> uses three different locking conventions in
-order to maximize compatibility with other mail software:
-C-Client folder locks, dot-locks, and file locks.
-</p><div class="refsect2" lang="en" xml:lang="en"><a id="id366036" shape="rect"> </a><h3>C-Client folder locks</h3><p>
-Mail software based on the <code class="literal">C-Client</code> library creates
-lock files named
-<code class="filename">/tmp/.<em class="replaceable"><code>dddddd</code></em>.<em class="replaceable"><code>iiiiii</code></em></code>.
-Here, <em class="replaceable"><code>dddddd</code></em> and <em class="replaceable"><code>iiiiii</code></em>
-are the device number and the inode number of the mailbox file
-(the <em class="structfield"><code>st_dev</code></em> and <em class="structfield"><code>st_ino</code></em>
-fields in the inode), in hexadecimal.
-If the process ID saved in the C-Client folder lock file is not valid,
-<span class="command"><strong>lockmail</strong></span> concludes that it's a stale lock file, and
-will remove it.</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
-A race condition exists where a <code class="literal">C-Client</code> process is
-killed after it creates a lock file, but before saving its process ID in the
-lock file.
-The race window is very small, but it exists.
-The <code class="literal">C-Client</code> library does not appear to ever clear out
-the lock file.</p><p>
-<span class="command"><strong>lockmail</strong></span>
-attempts to resolve this race condition by deleting zero-length lock files
-that are at least five minutes old.</p></div></div><div class="refsect2" lang="en" xml:lang="en"><a id="id366638" shape="rect"> </a><h3>dot-locks</h3><p>
-<span class="command"><strong>lockmail</strong></span>
-also creates, and honors dot-lock files.
-Dot-lock files are first created as temporary files, then linked to
-<code class="filename"><em class="replaceable"><code>lockfile</code></em>.lock</code>.
-The link operation fails if the dot-lock file already exists.
-<span class="command"><strong>lockmail</strong></span>
-uses an enhanced method of dot-locking, where its process ID, and the name
-of the server where <span class="command"><strong>lockmail</strong></span> is running is also saved
-in its dot-lock file.
-If the operation fails due to an existing dot-lock file that was created
-by another <span class="command"><strong>lockmail</strong></span> process on the same server, and the
-process ID no longer exists, this stale dot-lock file is removed immediately.
-In all other situations a dot-lock file older than five minutes is considered
-stale, and removed.
-</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
-A failure to create a dot-lock file is silently ignored if the reason for
-the failure is because
-<span class="command"><strong>lockmail</strong></span>
-does not have the write permission in the dot-lock file's directory.
-The incoming mail spool directory (usually
-<code class="filename">/var/mail</code>)
-typically does not have global write permissions, so the attempt to
-create the dot-lock file in the spool directory will fail, and
-<span class="command"><strong>lockmail</strong></span>
-will be content with using file-locking only.
-</p></div></div><div class="refsect2" lang="en" xml:lang="en"><a id="id366198" shape="rect"> </a><h3>File locks</h3><p>
-The final locking mechanism
-<span class="command"><strong>lockmail</strong></span>
-uses is the operating system's file locking facility.
-If
-<span class="command"><strong>lockmail</strong></span>
-fails to obtain all three locks,
-<span class="command"><strong>lockmail</strong></span>
-will sleep for five seconds and try again.
-The only exception is a failure to create a dot-lock because of no write
-access to the dot-lock file's directory, which is ignored.
-If
-<span class="command"><strong>lockmail</strong></span>
-still fails to obtain all required locks in the amount of time specified
-by the <code class="option">-t</code> option (or its default value),
-<span class="command"><strong>lockmail</strong></span> will terminate with the
-<code class="literal">EX_TEMPFAIL</code> exit code.
-</p><p>
-<span class="command"><strong>lockmail</strong></span>
-runs <em class="replaceable"><code>program</code></em> after obtaining the last file
-lock, waits until <em class="replaceable"><code>program</code></em> terminates, and
-releases all locks.
-<em class="replaceable"><code>program</code></em> must terminate before any of the locks
-obtained by <span class="command"><strong>lockmail</strong></span> expire, and are considered stale.
-<span class="command"><strong>lockmail</strong></span> will then terminate with the same exit code
-as <em class="replaceable"><code>program</code></em>.</p></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="id366286" shape="rect"> </a><h2>EXIT STATUS</h2><p>
-<span class="command"><strong>lockmail</strong></span> terminates with the same exit status as
-<em class="replaceable"><code>program</code></em>
-<span class="command"><strong>lockmail</strong></span> terminates with the <code class="literal">EX_TEMPFAIL</code>
-exit status if it was unable to obtain a lock, or if
-<em class="replaceable"><code>program</code></em>
-was killed by a signal.</p></div><div class="refsect1" lang="en" xml:lang="en"><a id="id366320" shape="rect"> </a><h2>SEE ALSO</h2><p>
-<a class="ulink" href="maildrop.html" target="_top" shape="rect"><span class="citerefentry"><span class="refentrytitle">maildrop</span>(1)</span></a>,
-<span class="citerefentry"><span class="refentrytitle">sendmail</span>(8)</span>.
-</p></div></div></body></html>
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