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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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  19 <div id="path">
  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. Each server process may answer incoming
  37     requests, and a parent process manages the size of the server pool.
  38     It is appropriate for sites that need to avoid
  39     threading for compatibility with non-thread-safe libraries.  It
  40     is also the best MPM for isolating each request, so that a problem
  41     with a single request will not affect any other.</p>
  42
  43     <p>This MPM is very self-regulating, so it is rarely necessary to
  44     adjust its configuration directives.  Most important is that
  45     <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code> be big enough to
  46     handle as many simultaneous requests as you expect to receive, but
  47     small enough to assure that there is enough physical RAM for all
  48     processes.</p>
  49 </div>
  50 <div id="quickview"><h3 class="directives">Directives</h3>
  51 <ul id="toc">
  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#maxclients">MaxClients</a></li>
  58 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxconnectionsperchild">MaxConnectionsPerChild</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/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#receivebuffersize">ReceiveBufferSize</a></li>
  64 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#scoreboardfile">ScoreBoardFile</a></li>
  65 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#sendbuffersize">SendBufferSize</a></li>
  66 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#serverlimit">ServerLimit</a></li>
  67 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#startservers">StartServers</a></li>
  68 <li><img alt="" src="../images/right.gif" /> <a href="mod_unixd.html#user">User</a></li>
  69 </ul>
  70 <h3>Topics</h3>
  71 <ul id="topics">
  72 <li><img alt="" src="../images/down.gif" /> <a href="#how-it-works">How it Works</a></li>
  73 </ul><h3>See also</h3>
  74 <ul class="seealso">
  75 <li><a href="../bind.html">Setting which addresses and ports Apache HTTP Server
  76 uses</a></li>
  77 </ul></div>
  78 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
  79 <div class="section">
  80 <h2><a name="how-it-works" id="how-it-works">How it Works</a></h2>
  81     <p>A single control process is responsible for launching child
  82     processes which listen for connections and serve them when they
  83     arrive. Apache httpd always tries to maintain several <dfn>spare</dfn>
  84     or idle server processes, which stand ready to serve incoming
  85     requests. In this way, clients do not need to wait for a new
  86     child processes to be forked before their requests can be
  87     served.</p>
  88
  89     <p>The <code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code>,
  90     <code class="directive"><a href="#minspareservers">MinSpareServers</a></code>,
  91     <code class="directive"><a href="#maxspareservers">MaxSpareServers</a></code>, and
  92     <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code> regulate how
  93     the parent process creates children to serve requests. In general,
  94     Apache httpd is very self-regulating, so most sites do not need to
  95     adjust these directives from their default values. Sites which
  96     need to serve more than 256 simultaneous requests may need to
  97     increase <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code>,
  98     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
  99     thrashing (swapping memory to disk and back). More information
 100     about tuning process creation is provided in the <a href="../misc/perf-tuning.html">performance hints</a>
 101     documentation.</p>
 102
 103     <p>While the parent process is usually started as <code>root</code>
 104     under Unix in order to bind to port 80, the child processes are
 105     launched by Apache httpd 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
 106     the privileges of the Apache httpd child processes. The child processes
 107     must be able to read all the content that will be served, but
 108     should have as few privileges beyond that as possible.</p>
 109
 110     <p><code class="directive"><a href="../mod/mpm_common.html#maxconnectionsperchild">MaxConnectionsPerChild</a></code>
 111     controls how frequently the server recycles processes by killing
 112     old ones and launching new ones.</p>
 113
 114     <p>This MPM uses the <code>mpm-accept</code> mutex to serialize
 115     access to incoming connections when subject to the thundering herd
 116     problem (generally, when there are multiple listening sockets).
 117     The implementation aspects of this mutex can be configured with the
 118     <code class="directive"><a href="../mod/core.html#mutex">Mutex</a></code> directive.  The <a href="../misc/perf-tuning.html">performance hints</a>
 119     documentation has additional information about this mutex.</p>
 120 </div>
 121 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 122 <div class="directive-section"><h2><a name="MaxSpareServers" id="MaxSpareServers">MaxSpareServers</a> <a name="maxspareservers" id="maxspareservers">Directive</a></h2>
 123 <table class="directive">
 124 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Maximum number of idle child server processes</td></tr>
 125 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MaxSpareServers <var>number</var></code></td></tr>
 126 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MaxSpareServers 10</code></td></tr>
 127 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
 128 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
 129 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>prefork</td></tr>
 130 </table>
 131     <p>The <code class="directive">MaxSpareServers</code> directive sets the
 132     desired maximum number of <em>idle</em> child server processes. An
 133     idle process is one which is not handling a request. If there are
 134     more than <code class="directive">MaxSpareServers</code> idle, then the
 135     parent process will kill off the excess processes.</p>
 136
 137     <p>Tuning of this parameter should only be necessary on very
 138     busy sites. Setting this parameter to a large number is almost
 139     always a bad idea. If you are trying to set the value equal to or lower than
 140     <code class="directive"><a href="#minspareservers">MinSpareServers</a></code>, Apache HTTP Server
 141     will automatically adjust it to <code class="directive">MinSpareServers</code><code> + 1</code>.</p>
 142
 143 <h3>See also</h3>
 144 <ul>
 145 <li><code class="directive"><a href="#minspareservers">MinSpareServers</a></code></li>
 146 <li><code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code></li>
 147 <li><code class="directive"><a href="../mod/mpm_common.html#maxsparethreads">MaxSpareThreads</a></code></li>
 148 </ul>
 149 </div>
 150 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 151 <div class="directive-section"><h2><a name="MinSpareServers" id="MinSpareServers">MinSpareServers</a> <a name="minspareservers" id="minspareservers">Directive</a></h2>
 152 <table class="directive">
 153 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Minimum number of idle child server processes</td></tr>
 154 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MinSpareServers <var>number</var></code></td></tr>
 155 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MinSpareServers 5</code></td></tr>
 156 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
 157 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
 158 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>prefork</td></tr>
 159 </table>
 160     <p>The <code class="directive">MinSpareServers</code> directive sets the
 161     desired minimum number of <em>idle</em> child server processes. An
 162     idle process is one which is not handling a request. If there are
 163     fewer than <code class="directive">MinSpareServers</code> idle, then the parent
 164     process creates new children: It will spawn one, wait a second, then spawn
 165     two, wait a second, then spawn four, and it will
 166     continue exponentially until it is spawning 32 children per second. It will
 167     stop whenever it satisfies the <code class="directive">MinSpareServers</code>
 168     setting.</p>
 169
 170     <p>Tuning of this parameter should only be necessary on very
 171     busy sites. Setting this parameter to a large number is almost
 172     always a bad idea.</p>
 173
 174 <h3>See also</h3>
 175 <ul>
 176 <li><code class="directive"><a href="#maxspareservers">MaxSpareServers</a></code></li>
 177 <li><code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code></li>
 178 <li><code class="directive"><a href="../mod/mpm_common.html#minsparethreads">MinSpareThreads</a></code></li>
 179 </ul>
 180 </div>
 181 </div>
 182 <div class="bottomlang">
 183 <p><span>Available Languages: </span><a href="../de/mod/prefork.html" hreflang="de" rel="alternate" title="Deutsch">&nbsp;de&nbsp;</a> |
 184 <a href="../en/mod/prefork.html" title="English">&nbsp;en&nbsp;</a> |
 185 <a href="../ja/mod/prefork.html" hreflang="ja" rel="alternate" title="Japanese">&nbsp;ja&nbsp;</a> |
 186 <a href="../tr/mod/prefork.html" hreflang="tr" rel="alternate" title="Türkçe">&nbsp;tr&nbsp;</a></p>
 187 </div><div id="footer">
 188 <p class="apache">Copyright 2011 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>
 189 <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>
 190 </body></html>