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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 2.3</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/">Documentation</a> &gt; <a href="../">Version 2.3</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> |
  27 <a href="../tr/mod/prefork.html" hreflang="tr" rel="alternate" title="Türkçe">&nbsp;tr&nbsp;</a></p>
  28 </div>
  29 <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>
  30 <tr><th><a href="module-dict.html#Status">Status:</a></th><td>MPM</td></tr>
  31 <tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>mpm_prefork_module</td></tr>
  32 <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>prefork.c</td></tr></table>
  33 <h3>Summary</h3>
  34
  35     <p>This Multi-Processing Module (MPM) implements a non-threaded,
  36     pre-forking web server that handles requests in a manner similar
  37     to Apache 1.3.  It is appropriate for sites that need to avoid
  38     threading for compatibility with non-thread-safe libraries.  It
  39     is also the best MPM for isolating each request, so that a problem
  40     with a single request will not affect any other.</p>
  41
  42     <p>This MPM is very self-regulating, so it is rarely necessary to
  43     adjust its configuration directives.  Most important is that
  44     <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code> be big enough to
  45     handle as many simultaneous requests as you expect to receive, but
  46     small enough to assure that there is enough physical RAM for all
  47     processes.</p>
  48 </div>
  49 <div id="quickview"><h3 class="directives">Directives</h3>
  50 <ul id="toc">
  51 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#acceptmutex">AcceptMutex</a></li>
  52 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#coredumpdirectory">CoreDumpDirectory</a></li>
  53 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#enableexceptionhook">EnableExceptionHook</a></li>
  54 <li><img alt="" src="../images/right.gif" /> <a href="mod_unixd.html#group">Group</a></li>
  55 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listen">Listen</a></li>
  56 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listenbacklog">ListenBacklog</a></li>
  57 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#lockfile">LockFile</a></li>
  58 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxclients">MaxClients</a></li>
  59 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxmemfree">MaxMemFree</a></li>
  60 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxrequestsperchild">MaxRequestsPerChild</a></li>
  61 <li><img alt="" src="../images/down.gif" /> <a href="#maxspareservers">MaxSpareServers</a></li>
  62 <li><img alt="" src="../images/down.gif" /> <a href="#minspareservers">MinSpareServers</a></li>
  63 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#pidfile">PidFile</a></li>
  64 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#receivebuffersize">ReceiveBufferSize</a></li>
  65 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#scoreboardfile">ScoreBoardFile</a></li>
  66 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#sendbuffersize">SendBufferSize</a></li>
  67 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#serverlimit">ServerLimit</a></li>
  68 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#startservers">StartServers</a></li>
  69 <li><img alt="" src="../images/right.gif" /> <a href="mod_unixd.html#user">User</a></li>
  70 </ul>
  71 <h3>Topics</h3>
  72 <ul id="topics">
  73 <li><img alt="" src="../images/down.gif" /> <a href="#how-it-works">How it Works</a></li>
  74 </ul><h3>See also</h3>
  75 <ul class="seealso">
  76 <li><a href="../bind.html">Setting which addresses and ports Apache
  77 uses</a></li>
  78 </ul></div>
  79 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
  80 <div class="section">
  81 <h2><a name="how-it-works" id="how-it-works">How it Works</a></h2>
  82     <p>A single control process is responsible for launching child
  83     processes which listen for connections and serve them when they
  84     arrive. Apache always tries to maintain several <dfn>spare</dfn>
  85     or idle server processes, which stand ready to serve incoming
  86     requests. In this way, clients do not need to wait for a new
  87     child processes to be forked before their requests can be
  88     served.</p>
  89
  90     <p>The <code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code>,
  91     <code class="directive"><a href="#minspareservers">MinSpareServers</a></code>,
  92     <code class="directive"><a href="#maxspareservers">MaxSpareServers</a></code>, and
  93     <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code> regulate how
  94     the parent process creates children to serve requests. In general,
  95     Apache is very self-regulating, so most sites do not need to
  96     adjust these directives from their default values. Sites which
  97     need to serve more than 256 simultaneous requests may need to
  98     increase <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code>,
  99     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
 100     thrashing (swapping memory to disk and back). More information
 101     about tuning process creation is provided in the <a href="../misc/perf-tuning.html">performance hints</a>
 102     documentation.</p>
 103
 104     <p>While the parent process is usually started as <code>root</code>
 105     under Unix in order to bind to port 80, the child processes are
 106     launched by Apache as a less-privileged user. The <code class="directive"><a href="../mod/mod_unixd.html#user">User</a></code> and <code class="directive"><a href="../mod/mod_unixd.html#group">Group</a></code> directives are used to set
 107     the privileges of the Apache child processes. The child processes
 108     must be able to read all the content that will be served, but
 109     should have as few privileges beyond that as possible.</p>
 110
 111     <p><code class="directive"><a href="../mod/mpm_common.html#maxrequestsperchild">MaxRequestsPerChild</a></code>
 112     controls how frequently the server recycles processes by killing
 113     old ones and launching new ones.</p>
 114 </div>
 115 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 116 <div class="directive-section"><h2><a name="MaxSpareServers" id="MaxSpareServers">MaxSpareServers</a> <a name="maxspareservers" id="maxspareservers">Directive</a></h2>
 117 <table class="directive">
 118 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Maximum number of idle child server processes</td></tr>
 119 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MaxSpareServers <var>number</var></code></td></tr>
 120 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MaxSpareServers 10</code></td></tr>
 121 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
 122 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
 123 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>prefork</td></tr>
 124 </table>
 125     <p>The <code class="directive">MaxSpareServers</code> directive sets the
 126     desired maximum number of <em>idle</em> child server processes. An
 127     idle process is one which is not handling a request. If there are
 128     more than <code class="directive">MaxSpareServers</code> idle, then the
 129     parent process will kill off the excess processes.</p>
 130
 131     <p>Tuning of this parameter should only be necessary on very
 132     busy sites. Setting this parameter to a large number is almost
 133     always a bad idea. If you are trying to set the value equal to or lower than
 134     <code class="directive"><a href="#minspareservers">MinSpareServers</a></code>, Apache
 135     will automatically adjust it to <code class="directive">MinSpareServers</code><code> + 1</code>.</p>
 136
 137 <h3>See also</h3>
 138 <ul>
 139 <li><code class="directive"><a href="#minspareservers">MinSpareServers</a></code></li>
 140 <li><code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code></li>
 141 </ul>
 142 </div>
 143 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 144 <div class="directive-section"><h2><a name="MinSpareServers" id="MinSpareServers">MinSpareServers</a> <a name="minspareservers" id="minspareservers">Directive</a></h2>
 145 <table class="directive">
 146 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Minimum number of idle child server processes</td></tr>
 147 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MinSpareServers <var>number</var></code></td></tr>
 148 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MinSpareServers 5</code></td></tr>
 149 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
 150 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
 151 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>prefork</td></tr>
 152 </table>
 153     <p>The <code class="directive">MinSpareServers</code> directive sets the
 154     desired minimum number of <em>idle</em> child server processes. An
 155     idle process is one which is not handling a request. If there are
 156     fewer than <code class="directive">MinSpareServers</code> idle, then the parent
 157     process creates new children at a maximum rate of 1 per second.</p>
 158
 159     <p>Tuning of this parameter should only be necessary on very
 160     busy sites. Setting this parameter to a large number is almost
 161     always a bad idea.</p>
 162
 163 <h3>See also</h3>
 164 <ul>
 165 <li><code class="directive"><a href="#maxspareservers">MaxSpareServers</a></code></li>
 166 <li><code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code></li>
 167 </ul>
 168 </div>
 169 </div>
 170 <div class="bottomlang">
 171 <p><span>Available Languages: </span><a href="../de/mod/prefork.html" hreflang="de" rel="alternate" title="Deutsch">&nbsp;de&nbsp;</a> |
 172 <a href="../en/mod/prefork.html" title="English">&nbsp;en&nbsp;</a> |
 173 <a href="../ja/mod/prefork.html" hreflang="ja" rel="alternate" title="Japanese">&nbsp;ja&nbsp;</a> |
 174 <a href="../tr/mod/prefork.html" hreflang="tr" rel="alternate" title="Türkçe">&nbsp;tr&nbsp;</a></p>
 175 </div><div id="footer">
 176 <p class="apache">Copyright 2008 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>
 177 <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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