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   8 <title>prefork - Apache HTTP Server</title>
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  15 <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>
  16 <p class="apache">Apache HTTP Server Version 2.1</p>
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  20 <a href="http://www.apache.org/">Apache</a> &gt; <a href="http://httpd.apache.org/">HTTP Server</a> &gt; <a href="http://httpd.apache.org/docs-project/">Documentation</a> &gt; <a href="../">Version 2.1</a> &gt; <a href="./">Modules</a></div>
  21 <div id="page-content">
  22 <div id="preamble"><h1>Apache MPM prefork</h1>
  23 <div class="toplang">
  24 <p><span>Available Languages: </span><a href="../de/mod/prefork.html" hreflang="de" rel="alternate" title="Deutsch">&nbsp;de&nbsp;</a> |
  25 <a href="../en/mod/prefork.html" title="English">&nbsp;en&nbsp;</a> |
  26 <a href="../ja/mod/prefork.html" hreflang="ja" rel="alternate" title="Japanese">&nbsp;ja&nbsp;</a></p>
  27 </div>
  28 <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>
  29 <tr><th><a href="module-dict.html#Status">Status:</a></th><td>MPM</td></tr>
  30 <tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>mpm_prefork_module</td></tr>
  31 <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>prefork.c</td></tr></table>
  32 <h3>Summary</h3>
  33
  34     <p>This Multi-Processing Module (MPM) implements a non-threaded,
  35     pre-forking web server that handles requests in a manner similar
  36     to Apache 1.3.  It is appropriate for sites that need to avoid
  37     threading for compatibility with non-thread-safe libraries.  It
  38     is also the best MPM for isolating each request, so that a problem
  39     with a single request will not affect any other.</p>
  40
  41     <p>This MPM is very self-regulating, so it is rarely necessary to
  42     adjust its configuration directives.  Most important is that
  43     <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code> be big enough to
  44     handle as many simultaneous requests as you expect to receive, but
  45     small enough to assure that there is enough physical RAM for all
  46     processes.</p>
  47 </div>
  48 <div id="quickview"><h3 class="directives">Directives</h3>
  49 <ul id="toc">
  50 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#acceptmutex">AcceptMutex</a></li>
  51 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#coredumpdirectory">CoreDumpDirectory</a></li>
  52 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#enableexceptionhook">EnableExceptionHook</a></li>
  53 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#group">Group</a></li>
  54 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listen">Listen</a></li>
  55 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listenbacklog">ListenBacklog</a></li>
  56 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#lockfile">LockFile</a></li>
  57 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxclients">MaxClients</a></li>
  58 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxmemfree">MaxMemFree</a></li>
  59 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxrequestsperchild">MaxRequestsPerChild</a></li>
  60 <li><img alt="" src="../images/down.gif" /> <a href="#maxspareservers">MaxSpareServers</a></li>
  61 <li><img alt="" src="../images/down.gif" /> <a href="#minspareservers">MinSpareServers</a></li>
  62 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#pidfile">PidFile</a></li>
  63 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#scoreboardfile">ScoreBoardFile</a></li>
  64 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#sendbuffersize">SendBufferSize</a></li>
  65 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#serverlimit">ServerLimit</a></li>
  66 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#startservers">StartServers</a></li>
  67 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#user">User</a></li>
  68 </ul>
  69 <h3>Topics</h3>
  70 <ul id="topics">
  71 <li><img alt="" src="../images/down.gif" /> <a href="#how-it-works">How it Works</a></li>
  72 </ul><h3>See also</h3>
  73 <ul class="seealso">
  74 <li><a href="../bind.html">Setting which addresses and ports Apache
  75 uses</a></li>
  76 </ul></div>
  77 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
  78 <div class="section">
  79 <h2><a name="how-it-works" id="how-it-works">How it Works</a></h2>
  80     <p>A single control process is responsible for launching child
  81     processes which listen for connections and serve them when they
  82     arrive. Apache always tries to maintain several <dfn>spare</dfn>
  83     or idle server processes, which stand ready to serve incoming
  84     requests. In this way, clients do not need to wait for a new
  85     child processes to be forked before their requests can be
  86     served.</p>
  87
  88     <p>The <code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code>,
  89     <code class="directive"><a href="#minspareservers">MinSpareServers</a></code>,
  90     <code class="directive"><a href="#maxspareservers">MaxSpareServers</a></code>, and
  91     <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code> regulate how
  92     the parent process creates children to serve requests. In general,
  93     Apache is very self-regulating, so most sites do not need to
  94     adjust these directives from their default values. Sites which
  95     need to serve more than 256 simultaneous requests may need to
  96     increase <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code>,
  97     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
  98     thrashing (swapping memory to disk and back). More information
  99     about tuning process creation is provided in the <a href="../misc/perf-tuning.html">performance hints</a>
 100     documentation.</p>
 101
 102     <p>While the parent process is usually started as <code>root</code>
 103     under Unix in order to bind to port 80, the child processes are
 104     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
 105     the privileges of the Apache child processes. The child processes
 106     must be able to read all the content that will be served, but
 107     should have as few privileges beyond that as possible.</p>
 108
 109     <p><code class="directive"><a href="../mod/mpm_common.html#maxrequestsperchild">MaxRequestsPerChild</a></code>
 110     controls how frequently the server recycles processes by killing
 111     old ones and launching new ones.</p>
 112 </div>
 113 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 114 <div class="directive-section"><h2><a name="MaxSpareServers" id="MaxSpareServers">MaxSpareServers</a> <a name="maxspareservers" id="maxspareservers">Directive</a></h2>
 115 <table class="directive">
 116 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Maximum number of idle child server processes</td></tr>
 117 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MaxSpareServers <var>number</var></code></td></tr>
 118 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MaxSpareServers 10</code></td></tr>
 119 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
 120 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
 121 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>prefork</td></tr>
 122 </table>
 123     <p>The <code class="directive">MaxSpareServers</code> directive sets the
 124     desired maximum number of <em>idle</em> child server processes. An
 125     idle process is one which is not handling a request. If there are
 126     more than <code class="directive">MaxSpareServers</code> idle, then the
 127     parent process will kill off the excess processes.</p>
 128
 129     <p>Tuning of this parameter should only be necessary on very
 130     busy sites. Setting this parameter to a large number is almost
 131     always a bad idea. If you are trying to set the value equal to or lower than
 132     <code class="directive"><a href="#minspareservers">MinSpareServers</a></code>, Apache
 133     will automatically adjust it to <code class="directive">MinSpareServers</code><code> + 1</code>.</p>
 134
 135 <h3>See also</h3>
 136 <ul>
 137 <li><code class="directive"><a href="#minspareservers">MinSpareServers</a></code></li>
 138 <li><code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code></li>
 139 </ul>
 140 </div>
 141 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 142 <div class="directive-section"><h2><a name="MinSpareServers" id="MinSpareServers">MinSpareServers</a> <a name="minspareservers" id="minspareservers">Directive</a></h2>
 143 <table class="directive">
 144 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Minimum number of idle child server processes</td></tr>
 145 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MinSpareServers <var>number</var></code></td></tr>
 146 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MinSpareServers 5</code></td></tr>
 147 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
 148 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
 149 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>prefork</td></tr>
 150 </table>
 151     <p>The <code class="directive">MinSpareServers</code> directive sets the
 152     desired minimum number of <em>idle</em> child server processes. An
 153     idle process is one which is not handling a request. If there are
 154     fewer than <code class="directive">MinSpareServers</code> idle, then the parent
 155     process creates new children at a maximum rate of 1 per second.</p>
 156
 157     <p>Tuning of this parameter should only be necessary on very
 158     busy sites. Setting this parameter to a large number is almost
 159     always a bad idea.</p>
 160
 161 <h3>See also</h3>
 162 <ul>
 163 <li><code class="directive"><a href="#maxspareservers">MaxSpareServers</a></code></li>
 164 <li><code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code></li>
 165 </ul>
 166 </div>
 167 </div>
 168 <div class="bottomlang">
 169 <p><span>Available Languages: </span><a href="../de/mod/prefork.html" hreflang="de" rel="alternate" title="Deutsch">&nbsp;de&nbsp;</a> |
 170 <a href="../en/mod/prefork.html" title="English">&nbsp;en&nbsp;</a> |
 171 <a href="../ja/mod/prefork.html" hreflang="ja" rel="alternate" title="Japanese">&nbsp;ja&nbsp;</a></p>
 172 </div><div id="footer">
 173 <p class="apache">Copyright 1999-2004 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>
 174 <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></div>
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