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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">&nbsp;de&nbsp;</a> | <a href="../en/mod/prefork.html">&nbsp;en&nbsp;</a> | <a href="../ja/mod/prefork.html">&nbsp;ja&nbsp;</a></p>
  25 </div>
  26 <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>
  27 <tr><th><a href="module-dict.html#Status">Status:</a></th><td>MPM</td></tr>
  28 <tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>mpm_prefork_module</td></tr>
  29 <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>prefork.c</td></tr></table>
  30 <h3>Summary</h3>
  31
  32     <p>This Multi-Processing Module (MPM) implements a non-threaded,
  33     pre-forking web server that handles requests in a manner similar
  34     to Apache 1.3.  It is appropriate for sites that need to avoid
  35     threading for compatibility with non-thread-safe libraries.  It
  36     is also the best MPM for isolating each request, so that a problem
  37     with a single request will not affect any other.</p>
  38
  39     <p>This MPM is very self-regulating, so it is rarely necessary to
  40     adjust its configuration directives.  Most important is that
  41     <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code> be big enough to
  42     handle as many simultaneous requests as you expect to receive, but
  43     small enough to assure that there is enough physical RAM for all
  44     processes.</p>
  45 </div>
  46 <div id="quickview"><h3 class="directives">Directives</h3>
  47 <ul id="toc">
  48 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#acceptmutex">AcceptMutex</a></li>
  49 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#bs2000account">BS2000Account</a></li>
  50 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#coredumpdirectory">CoreDumpDirectory</a></li>
  51 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#group">Group</a></li>
  52 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listen">Listen</a></li>
  53 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listenbacklog">ListenBacklog</a></li>
  54 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#lockfile">LockFile</a></li>
  55 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxclients">MaxClients</a></li>
  56 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxmemfree">MaxMemFree</a></li>
  57 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxrequestsperchild">MaxRequestsPerChild</a></li>
  58 <li><img alt="" src="../images/down.gif" /> <a href="#maxspareservers">MaxSpareServers</a></li>
  59 <li><img alt="" src="../images/down.gif" /> <a href="#minspareservers">MinSpareServers</a></li>
  60 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#pidfile">PidFile</a></li>
  61 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#scoreboardfile">ScoreBoardFile</a></li>
  62 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#sendbuffersize">SendBufferSize</a></li>
  63 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#serverlimit">ServerLimit</a></li>
  64 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#startservers">StartServers</a></li>
  65 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#user">User</a></li>
  66 </ul>
  67 <h3>Topics</h3>
  68 <ul id="topics">
  69 <li><img alt="" src="../images/down.gif" /> <a href="#how-it-works">How it Works</a></li>
  70 </ul><h3>See also</h3>
  71 <ul class="seealso">
  72 <li><a href="../bind.html">Setting which addresses and ports Apache
  73 uses</a></li>
  74 </ul></div>
  75 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
  76 <div class="section">
  77 <h2><a name="how-it-works" id="how-it-works">How it Works</a></h2>
  78     <p>A single control process is responsible for launching child
  79     processes which listen for connections and serve them when they
  80     arrive. Apache always tries to maintain several <dfn>spare</dfn>
  81     or idle server processes, which stand ready to serve incoming
  82     requests. In this way, clients do not need to wait for a new
  83     child processes to be forked before their requests can be
  84     served.</p>
  85
  86     <p>The <code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code>,
  87     <code class="directive"><a href="#minspareservers">MinSpareServers</a></code>,
  88     <code class="directive"><a href="#maxspareservers">MaxSpareServers</a></code>, and
  89     <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code> regulate how
  90     the parent process creates children to serve requests. In general,
  91     Apache is very self-regulating, so most sites do not need to
  92     adjust these directives from their default values. Sites which
  93     need to serve more than 256 simultaneous requests may need to
  94     increase <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code>,
  95     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
  96     thrashing (swapping memory to disk and back). More information
  97     about tuning process creation is provided in the <a href="../misc/perf-tuning.html">performance hints</a>
  98     documentation.</p>
  99
 100     <p>While the parent process is usually started as <code>root</code>
 101     under Unix in order to bind to port 80, the child processes are
 102     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
 103     the privileges of the Apache child processes. The child processes
 104     must be able to read all the content that will be served, but
 105     should have as few privileges beyond that as possible.</p>
 106
 107     <p><code class="directive"><a href="../mod/mpm_common.html#maxrequestsperchild">MaxRequestsPerChild</a></code>
 108     controls how frequently the server recycles processes by killing
 109     old ones and launching new ones.</p>
 110 </div>
 111 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 112 <div class="directive-section"><h2><a name="MaxSpareServers" id="MaxSpareServers">MaxSpareServers</a> <a name="maxspareservers" id="maxspareservers">Directive</a></h2>
 113 <table class="directive">
 114 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Maximum number of idle child server processes</td></tr>
 115 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MaxSpareServers <var>number</var><br /></code></td></tr>
 116 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MaxSpareServers 10</code></td></tr>
 117 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
 118 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
 119 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>prefork</td></tr>
 120 </table>
 121     <p>The <code class="directive">MaxSpareServers</code> directive sets the
 122     desired maximum number of <em>idle</em> child server processes. An
 123     idle process is one which is not handling a request. If there are
 124     more than <code class="directive">MaxSpareServers</code> idle, then the
 125     parent process will kill off the excess processes.</p>
 126
 127     <p>Tuning of this parameter should only be necessary on very
 128     busy sites. Setting this parameter to a large number is almost
 129     always a bad idea. If you are trying to set the value lower than
 130     <code class="directive"><a href="#minspareservers">MinSpareServers</a></code>, Apache
 131     will automatically adjust it to <code class="directive">MinSpareServers</code><code> + 1</code>.</p>
 132
 133 <h3>See also</h3>
 134 <ul>
 135 <li><code class="directive"><a href="#minspareservers">MinSpareServers</a></code></li>
 136 <li><code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code></li>
 137 </ul>
 138 </div>
 139 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 140 <div class="directive-section"><h2><a name="MinSpareServers" id="MinSpareServers">MinSpareServers</a> <a name="minspareservers" id="minspareservers">Directive</a></h2>
 141 <table class="directive">
 142 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Minimum number of idle child server processes</td></tr>
 143 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MinSpareServers <var>number</var></code></td></tr>
 144 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MinSpareServers 5</code></td></tr>
 145 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
 146 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
 147 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>prefork</td></tr>
 148 </table>
 149     <p>The <code class="directive">MinSpareServers</code> directive sets the
 150     desired minimum number of <em>idle</em> child server processes. An
 151     idle process is one which is not handling a request. If there are
 152     fewer than <code class="directive">MinSpareServers</code> idle, then the parent
 153     process creates new children at a maximum rate of 1 per second.</p>
 154
 155     <p>Tuning of this parameter should only be necessary on very
 156     busy sites. Setting this parameter to a large number is almost
 157     always a bad idea.</p>
 158
 159 <h3>See also</h3>
 160 <ul>
 161 <li><code class="directive"><a href="#maxspareservers">MaxSpareServers</a></code></li>
 162 <li><code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code></li>
 163 </ul>
 164 </div>
 165 </div>
 166 <div class="bottomlang">
 167 <p><span>Available Languages: </span><a href="../de/mod/prefork.html">&nbsp;de&nbsp;</a> | <a href="../en/mod/prefork.html">&nbsp;en&nbsp;</a> | <a href="../ja/mod/prefork.html">&nbsp;ja&nbsp;</a></p>
 168 </div><div id="footer">
 169 <p class="apache">Maintained by the <a href="http://httpd.apache.org/docs-project/">Apache HTTP Server Documentation Project</a></p>
 170 <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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