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<title>prefork - Apache HTTP Server</title>
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<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../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 2.2</p>
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<div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div>
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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 2.2</a> > <a href="./">Modules</a></div>
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<div id="page-content">
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<div id="preamble"><h1>Apache MPM prefork</h1>
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<p><span>Available Languages: </span><a href="../de/mod/prefork.html" hreflang="de" rel="alternate" title="Deutsch"> de </a> |
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<a href="../en/mod/prefork.html" title="English"> en </a> |
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<a href="../ja/mod/prefork.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a></p>
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<table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Implements a non-threaded, pre-forking web server</td></tr>
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<tr><th><a href="module-dict.html#Status">Status:</a></th><td>MPM</td></tr>
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<tr><th><a href="module-dict.html#ModuleIdentifier">Module�Identifier:</a></th><td>mpm_prefork_module</td></tr>
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<tr><th><a href="module-dict.html#SourceFile">Source�File:</a></th><td>prefork.c</td></tr></table>
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<p>This Multi-Processing Module (MPM) implements a non-threaded,
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pre-forking web server that handles requests in a manner similar
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to Apache 1.3. It is appropriate for sites that need to avoid
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threading for compatibility with non-thread-safe libraries. It
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is also the best MPM for isolating each request, so that a problem
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with a single request will not affect any other.</p>
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<p>This MPM is very self-regulating, so it is rarely necessary to
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adjust its configuration directives. Most important is that
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<code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code> be big enough to
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handle as many simultaneous requests as you expect to receive, but
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small enough to assure that there is enough physical RAM for all
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<div id="quickview"><h3 class="directives">Directives</h3>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#acceptmutex">AcceptMutex</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#coredumpdirectory">CoreDumpDirectory</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#enableexceptionhook">EnableExceptionHook</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#group">Group</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listen">Listen</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listenbacklog">ListenBacklog</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#lockfile">LockFile</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxclients">MaxClients</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxmemfree">MaxMemFree</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxrequestsperchild">MaxRequestsPerChild</a></li>
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<li><img alt="" src="../images/down.gif" /> <a href="#maxspareservers">MaxSpareServers</a></li>
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<li><img alt="" src="../images/down.gif" /> <a href="#minspareservers">MinSpareServers</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#pidfile">PidFile</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#receivebuffersize">ReceiveBufferSize</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#scoreboardfile">ScoreBoardFile</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#sendbuffersize">SendBufferSize</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#serverlimit">ServerLimit</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#startservers">StartServers</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#user">User</a></li>
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<li><img alt="" src="../images/down.gif" /> <a href="#how-it-works">How it Works</a></li>
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</ul><h3>See also</h3>
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<li><a href="../bind.html">Setting which addresses and ports Apache
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<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
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<h2><a name="how-it-works" id="how-it-works">How it Works</a></h2>
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<p>A single control process is responsible for launching child
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processes which listen for connections and serve them when they
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arrive. Apache always tries to maintain several <dfn>spare</dfn>
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or idle server processes, which stand ready to serve incoming
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requests. In this way, clients do not need to wait for a new
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child processes to be forked before their requests can be
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<p>The <code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code>,
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<code class="directive"><a href="#minspareservers">MinSpareServers</a></code>,
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<code class="directive"><a href="#maxspareservers">MaxSpareServers</a></code>, and
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<code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code> regulate how
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the parent process creates children to serve requests. In general,
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Apache is very self-regulating, so most sites do not need to
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adjust these directives from their default values. Sites which
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need to serve more than 256 simultaneous requests may need to
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increase <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code>,
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while sites with limited memory may need to decrease <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code> to keep the server from
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thrashing (swapping memory to disk and back). More information
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about tuning process creation is provided in the <a href="../misc/perf-tuning.html">performance hints</a>
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<p>While the parent process is usually started as <code>root</code>
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under Unix in order to bind to port 80, the child processes are
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launched by Apache as a less-privileged user. The <code class="directive"><a href="../mod/mpm_common.html#user">User</a></code> and <code class="directive"><a href="../mod/mpm_common.html#group">Group</a></code> directives are used to set
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the privileges of the Apache child processes. The child processes
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must be able to read all the content that will be served, but
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should have as few privileges beyond that as possible.</p>
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<p><code class="directive"><a href="../mod/mpm_common.html#maxrequestsperchild">MaxRequestsPerChild</a></code>
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controls how frequently the server recycles processes by killing
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old ones and launching new ones.</p>
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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="MaxSpareServers" id="MaxSpareServers">MaxSpareServers</a> <a name="maxspareservers" id="maxspareservers">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>Maximum number of idle child server processes</td></tr>
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<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MaxSpareServers <var>number</var></code></td></tr>
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<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MaxSpareServers 10</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>MPM</td></tr>
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<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>prefork</td></tr>
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<p>The <code class="directive">MaxSpareServers</code> directive sets the
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desired maximum number of <em>idle</em> child server processes. An
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idle process is one which is not handling a request. If there are
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more than <code class="directive">MaxSpareServers</code> idle, then the
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parent process will kill off the excess processes.</p>
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<p>Tuning of this parameter should only be necessary on very
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busy sites. Setting this parameter to a large number is almost
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always a bad idea. If you are trying to set the value equal to or lower than
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<code class="directive"><a href="#minspareservers">MinSpareServers</a></code>, Apache
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will automatically adjust it to <code class="directive">MinSpareServers</code><code> + 1</code>.</p>
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<li><code class="directive"><a href="#minspareservers">MinSpareServers</a></code></li>
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<li><code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code></li>
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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="MinSpareServers" id="MinSpareServers">MinSpareServers</a> <a name="minspareservers" id="minspareservers">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>Minimum number of idle child server processes</td></tr>
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<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MinSpareServers <var>number</var></code></td></tr>
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<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MinSpareServers 5</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>MPM</td></tr>
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<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>prefork</td></tr>
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<p>The <code class="directive">MinSpareServers</code> directive sets the
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desired minimum number of <em>idle</em> child server processes. An
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idle process is one which is not handling a request. If there are
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fewer than <code class="directive">MinSpareServers</code> idle, then the parent
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process creates new children at a maximum rate of 1 per second.</p>
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<p>Tuning of this parameter should only be necessary on very
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busy sites. Setting this parameter to a large number is almost
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always a bad idea.</p>
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<li><code class="directive"><a href="#maxspareservers">MaxSpareServers</a></code></li>
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<li><code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code></li>
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<div class="bottomlang">
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<p><span>Available Languages: </span><a href="../de/mod/prefork.html" hreflang="de" rel="alternate" title="Deutsch"> de </a> |
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<a href="../en/mod/prefork.html" title="English"> en </a> |
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<a href="../ja/mod/prefork.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a></p>
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</div><div id="footer">
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<p class="apache">Copyright 2006 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
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