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<?xml version="1.0" encoding="ISO-8859-1"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head><!--
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XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
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This file is generated from xml source: DO NOT EDIT
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XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
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-->
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<title>mod_file_cache - Apache HTTP Server</title>
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<link href="../style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" />
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<link href="../style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" />
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<link href="../style/css/manual-print.css" rel="stylesheet" media="print" type="text/css" /><link rel="stylesheet" type="text/css" href="../style/css/prettify.css" />
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<script src="../style/scripts/prettify.js" type="text/javascript">
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</script>
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<link href="../images/favicon.ico" rel="shortcut icon" /></head>
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<body>
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<div id="page-header">
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<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/quickreference.html">Directives</a> | <a href="http://wiki.apache.org/httpd/FAQ">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p>
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<p class="apache">Apache HTTP Server Version 2.5</p>
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<img alt="" src="../images/feather.gif" /></div>
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<div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div>
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<div id="path">
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<a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="../">Version 2.5</a> > <a href="./">Modules</a></div>
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<div id="page-content">
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<div id="preamble"><h1>Apache Module mod_file_cache</h1>
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<div class="toplang">
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<p><span>Available Languages: </span><a href="../en/mod/mod_file_cache.html" title="English"> en </a> |
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<a href="../ko/mod/mod_file_cache.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
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</div>
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<table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Caches a static list of files in memory</td></tr>
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<tr><th><a href="module-dict.html#Status">Status:</a></th><td>Experimental</td></tr>
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<tr><th><a href="module-dict.html#ModuleIdentifier">Module<EFBFBD>Identifier:</a></th><td>file_cache_module</td></tr>
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<tr><th><a href="module-dict.html#SourceFile">Source<EFBFBD>File:</a></th><td>mod_file_cache.c</td></tr></table>
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<h3>Summary</h3>
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<div class="warning">
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This module should be used with care. You can easily create a broken
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site using <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code>, so read this document
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carefully.
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</div>
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<p><em>Caching</em> frequently requested files that change very
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infrequently is a technique for reducing server load.
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<code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> provides two techniques for caching
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frequently requested <em>static</em> files. Through configuration
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directives, you can direct <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> to either
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open then <code>mmap()</code> a file, or to pre-open a file and save
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the file's open <em>file handle</em>. Both techniques reduce server
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load when processing requests for these files by doing part of the work
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(specifically, the file I/O) for serving the file when the
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server is started rather than during each request.</p>
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<p>Notice: You cannot use this for speeding up CGI programs or
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other files which are served by special content handlers. It
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can only be used for regular files which are usually served by
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the Apache core content handler.</p>
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<p>This module is an extension of and borrows heavily from the
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<code>mod_mmap_static</code> module in Apache 1.3.</p>
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</div>
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<div id="quickview"><h3 class="directives">Directives</h3>
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<ul id="toc">
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<li><img alt="" src="../images/down.gif" /> <a href="#cachefile">CacheFile</a></li>
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<li><img alt="" src="../images/down.gif" /> <a href="#mmapfile">MMapFile</a></li>
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</ul>
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<h3>Topics</h3>
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<ul id="topics">
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<li><img alt="" src="../images/down.gif" /> <a href="#using">Using mod_file_cache</a></li>
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</ul><ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div>
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<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
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<div class="section">
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<h2><a name="using" id="using">Using mod_file_cache</a></h2>
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<p><code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> caches a list of statically
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configured files via <code class="directive"><a href="#mmapfile">MMapFile</a></code> or <code class="directive"><a href="#cachefile">CacheFile</a></code> directives in the main server configuration.</p>
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<p>Not all platforms support both directives. You will receive an error
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message in the server error log if you attempt to use an
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unsupported directive. If given an unsupported directive, the
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server will start but the file will not be cached. On platforms
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that support both directives, you should experiment with both to
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see which works best for you.</p>
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<h3>MMapFile Directive</h3>
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<p>The <code class="directive"><a href="#mmapfile">MMapFile</a></code>
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directive of <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> maps a list of
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statically configured files into memory through the system call
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<code>mmap()</code>. This system call is available on most modern
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Unix derivatives, but not on all. There are sometimes system-specific
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limits on the size and number of files that can be
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<code>mmap()</code>ed, experimentation is probably the easiest way
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to find out.</p>
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<p>This <code>mmap()</code>ing is done once at server start or
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restart, only. So whenever one of the mapped files changes on the
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filesystem you <em>have</em> to restart the server (see the <a href="../stopping.html">Stopping and Restarting</a> documentation).
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To reiterate that point: if the files are modified <em>in place</em>
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without restarting the server you may end up serving requests that
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are completely bogus. You should update files by unlinking the old
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copy and putting a new copy in place. Most tools such as
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<code>rdist</code> and <code>mv</code> do this. The reason why this
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modules doesn't take care of changes to the files is that this check
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would need an extra <code>stat()</code> every time which is a waste
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and against the intent of I/O reduction.</p>
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<h3>CacheFile Directive</h3>
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<p>The <code class="directive"><a href="#cachefile">CacheFile</a></code>
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directive of <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> opens an active
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<em>handle</em> or <em>file descriptor</em> to the file (or files)
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listed in the configuration directive and places these open file
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handles in the cache. When the file is requested, the server
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retrieves the handle from the cache and passes it to the
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<code>sendfile()</code> (or <code>TransmitFile()</code> on Windows),
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socket API.</p>
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<p>This file handle caching is done once at server start or
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restart, only. So whenever one of the cached files changes on
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the filesystem you <em>have</em> to restart the server (see the
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<a href="../stopping.html">Stopping and Restarting</a>
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documentation). To reiterate that point: if the files are
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modified <em>in place</em> without restarting the server you
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may end up serving requests that are completely bogus. You
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should update files by unlinking the old copy and putting a new
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copy in place. Most tools such as <code>rdist</code> and
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<code>mv</code> do this.</p>
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<div class="note"><h3>Note</h3>
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<p>Don't bother asking for a directive which recursively
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caches all the files in a directory. Try this instead... See the
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<code class="directive"><a href="../mod/core.html#include">Include</a></code> directive, and consider
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this command:</p>
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<div class="example"><p><code>
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find /www/htdocs -type f -print \<br />
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| sed -e 's/.*/mmapfile &/' > /www/conf/mmap.conf
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</code></p></div>
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</div>
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</div>
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<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
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<div class="directive-section"><h2><a name="CacheFile" id="CacheFile">CacheFile</a> <a name="cachefile" id="cachefile">Directive</a></h2>
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<table class="directive">
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<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Cache a list of file handles at startup time</td></tr>
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<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheFile <var>file-path</var> [<var>file-path</var>] ...</code></td></tr>
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<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
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<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Experimental</td></tr>
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<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_file_cache</td></tr>
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</table>
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<p>The <code class="directive">CacheFile</code> directive opens handles to
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one or more files (given as whitespace separated arguments) and
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places these handles into the cache at server startup
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time. Handles to cached files are automatically closed on a server
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shutdown. When the files have changed on the filesystem, the
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server should be restarted to re-cache them.</p>
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<p>Be careful with the <var>file-path</var> arguments: They have
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to literally match the filesystem path Apache's URL-to-filename
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translation handlers create. We cannot compare inodes or other
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stuff to match paths through symbolic links <em>etc.</em>
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because that again would cost extra <code>stat()</code> system
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calls which is not acceptable. This module may or may not work
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with filenames rewritten by <code class="module"><a href="../mod/mod_alias.html">mod_alias</a></code> or
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<code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>.</p>
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<div class="example"><h3>Example</h3><pre class="prettyprint lang-config">
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CacheFile /usr/local/apache/htdocs/index.html
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</pre>
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</div>
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</div>
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<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
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<div class="directive-section"><h2><a name="MMapFile" id="MMapFile">MMapFile</a> <a name="mmapfile" id="mmapfile">Directive</a></h2>
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<table class="directive">
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<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Map a list of files into memory at startup time</td></tr>
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<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MMapFile <var>file-path</var> [<var>file-path</var>] ...</code></td></tr>
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<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
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<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Experimental</td></tr>
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<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_file_cache</td></tr>
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</table>
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<p>The <code class="directive">MMapFile</code> directive maps one or more files
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(given as whitespace separated arguments) into memory at server
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startup time. They are automatically unmapped on a server
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shutdown. When the files have changed on the filesystem at
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least a <code>HUP</code> or <code>USR1</code> signal should be send to
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the server to re-<code>mmap()</code> them.</p>
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<p>Be careful with the <var>file-path</var> arguments: They have
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to literally match the filesystem path Apache's URL-to-filename
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translation handlers create. We cannot compare inodes or other
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stuff to match paths through symbolic links <em>etc.</em>
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because that again would cost extra <code>stat()</code> system
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calls which is not acceptable. This module may or may not work
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with filenames rewritten by <code class="module"><a href="../mod/mod_alias.html">mod_alias</a></code> or
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<code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>.</p>
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<div class="example"><h3>Example</h3><pre class="prettyprint lang-config">
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MMapFile /usr/local/apache/htdocs/index.html
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</pre>
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</div>
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</div>
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</div>
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<div class="bottomlang">
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<p><span>Available Languages: </span><a href="../en/mod/mod_file_cache.html" title="English"> en </a> |
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<a href="../ko/mod/mod_file_cache.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
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</div><div class="top"><a href="#page-header"><img src="../images/up.gif" alt="top" /></a></div><div class="section"><h2><a id="comments_section" name="comments_section">Comments</a></h2><div class="warning"><strong>Notice:</strong><br />This is not a Q&A section. Comments placed here should be pointed towards suggestions on improving the documentation or server, and may be removed again by our moderators if they are either implemented or considered invalid/off-topic. Questions on how to manage the Apache HTTP Server should be directed at either our IRC channel, #httpd, on Freenode, or sent to our <a href="http://httpd.apache.org/lists.html">mailing lists</a>.</div>
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