<?xml version="1.0"?> <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" type="text/css" href="style.css"/><meta name="generator" content="DocBook XSL Stylesheets V1.76.1"/><link rel="home" href="#id302572" 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"/><!-- Copyright 1998 - 2009 Double Precision, Inc. See COPYING for distribution information. --></head><body><div class="refentry" title="lockmail"><a id="id302572" shape="rect"> </a><div class="titlepage"/><div class="refnamediv"><h2>Name</h2><p>lockmail — create mail lock files</p></div><div class="refsynopsisdiv" title="Synopsis"><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" title="DESCRIPTION"><a id="id302346" 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 successfully 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" title="OPTIONS"><a id="id336834" 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" title="DESCRIPTION"><a id="id336878" 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" title="C-Client folder locks"><a id="id336900" 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" title="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" title="dot-locks"><a id="id301472" 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" title="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" title="File locks"><a id="id301546" 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" title="EXIT STATUS"><a id="id301795" 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" title="SEE ALSO"><a id="id301830" 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>