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<html xmlns="http://www.w3.org/TR/xhtml1/strict"><head><!--
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--><title>prefork- Apache HTTP Server</title><link href="../style/manual.css" type="text/css" rel="stylesheet"/></head><body><blockquote><div align="center"><img src="../images/sub.gif" alt="[APACHE DOCUMENTATION]"/><h3>Apache HTTP Server Version 2.0</h3></div><h1 align="center">Apache Module prefork</h1><table cellspacing="1" cellpadding="0" bgcolor="#cccccc"><tr><td><table bgcolor="#ffffff"><tr><td valign="top"><span class="help">Description:</span></td><td>Implements a non-threaded, pre-forking web server</td></tr><tr><td><a href="module-dict.html#Status" class="help">Status:</a></td><td>MPM</td></tr><tr><td><a href="module-dict.html#ModuleIdentifier" class="help">Module Identifier:</a></td><td>mpm_prefork_module</td></tr></table></td></tr></table><h2>Summary</h2>
<p>This Multi-Processing Module (MPM) implements a non-threaded,
pre-forking web server that handles requests in a manner similar
to Apache 1.3. It is appropriate for sites that need to avoid
threading for compatibility with non-thread-safe libraries. It
is also the best MPM for isolating each request, so that a problem
with a single request will not affect any other.</p>
<p>This MPM is very self-regulating, so it is rarely necessary to
adjust its configuration directives. Most important is that
<a href="mpm_common.html#maxclients" class="directive"><code class="directive">MaxClients</code></a> be big enough to
handle as many simultaneous requests as you expect to receive, but
small enough to assure that there is enough physical RAM for all
processes.</p>
<h2>Directives</h2><ul><li><a href="#acceptmutex">AcceptMutex</a></li><li><a href="mpm_common.html#coredumpdirectory">CoreDumpDirectory</a></li><li><a href="mpm_common.html#group">Group</a></li><li><a href="mpm_common.html#listen">Listen</a></li><li><a href="mpm_common.html#listenbacklog">ListenBacklog</a></li><li><a href="mpm_common.html#lockfile">LockFile</a></li><li><a href="mpm_common.html#maxclients">MaxClients</a></li><li><a href="mpm_common.html#maxrequestsperchild">MaxRequestsPerChild</a></li><li><a href="mpm_common.html#maxspareservers">MaxSpareServers</a></li><li><a href="#maxspareservers">MaxSpareServers</a></li><li><a href="mpm_common.html#minspareservers">MinSpareServers</a></li><li><a href="#minspareservers">MinSpareServers</a></li><li><a href="mpm_common.html#pidfile">PidFile</a></li><li><a href="mpm_common.html#scoreboardfile">ScoreBoardFile</a></li><li><a href="mpm_common.html#sendbuffersize">SendBufferSize</a></li><li><a href="mpm_common.html#serverlimit">ServerLimit</a></li><li><a href="mpm_common.html#startservers">StartServers</a></li><li><a href="mpm_common.html#user">User</a></li></ul><p><strong>See also </strong></p><ul><li><a href="../bind.html">Setting which addresses and
ports Apache uses</a></li></ul><h2>How it Works</h2>
<p>A single control process is responsible for launching child
processes which listen for connections and serve them when they
arrive. Apache always tries to maintain several <em>spare</em>
or idle server processes, which stand ready to serve incoming
requests. In this way, clients do not need to wait for a new
child processes to be forked before their requests can be
served.</p>
<p>The <a href="mpm_common.html#startservers" class="directive"><code class="directive">StartServers</code></a>,
<a href="#minspareservers" class="directive"><code class="directive">MinSpareServers</code></a>,
<a href="#maxspareservers" class="directive"><code class="directive">MaxSpareServers</code></a>, and
<a href="mpm_common.html#maxclients" class="directive"><code class="directive">MaxClients</code></a> regulate how
the parent process creates children to serve requests. In general,
Apache is very self-regulating, so most sites do not need to
adjust these directives from their default values. Sites which
need to serve more than 256 simultaneous requests may need to
increase <a href="mpm_common.html#maxclients" class="directive"><code class="directive">MaxClients</code></a>,
while sites with limited memory may need to decrease <a href="mpm_common.html#maxclients" class="directive"><code class="directive">MaxClients</code></a> to keep the server from
thrashing (swapping memory to disk and back). More information
about tuning process creation is provided in the <a href="../misc/perf-tuning.html">performance hints</a>
documentation.</p>
<p>While the parent process is usually started as root under Unix
in order to bind to port 80, the child processes are launched by
Apache as a less-privileged user. The <a href="mpm_common.html#user" class="directive"><code class="directive">User</code></a> and <a href="mpm_common.html#group" class="directive"><code class="directive">Group</code></a> directives are used to set
the privileges of the Apache child processes. The child processes
must be able to read all the content that will be served, but
should have as few privileges beyond that as possible.</p>
<p><a href="mpm_common.html#maxrequestsperchild" class="directive"><code class="directive">MaxRequestsPerChild</code></a>
controls how frequently the server recycles processes by killing
old ones and launching new ones.</p>
<hr/><h2><a name="AcceptMutex">AcceptMutex</a> <a name="acceptmutex">Directive</a></h2><table cellpadding="1" cellspacing="0" border="0" bgcolor="#cccccc"><tr><td><table bgcolor="#ffffff"><tr><td nowrap="nowrap"><strong>Description: </strong></td><td>Method that Apache uses to serialize multiple children
accepting requests on network sockets</td></tr><tr><td nowrap="nowrap"><a href="directive-dict.html#Syntax" class="help">Syntax:</a></td><td>AcceptMutex default|<em>method</em></td></tr><tr><td nowrap="nowrap"><a href="directive-dict.html#Default" class="help">Default:</a></td><td><code>AcceptMutex default</code></td></tr><tr><td nowrap="nowrap"><a href="directive-dict.html#Context" class="help">Context:</a></td><td>server config</td></tr><tr><td nowrap="nowrap"><a href="directive-dict.html#Status" class="help">Status:</a></td><td>MPM</td></tr><tr><td nowrap="nowrap"><a href="directive-dict.html#Module" class="help">Module:</a></td><td>prefork</td></tr></table></td></tr></table>
<p>The <code class="directive">AcceptMutex</code> directives sets the
method that Apache uses to serialize multiple children accepting
requests on network sockets. Prior to Apache 2.0, the method was
selectable only at compile time. The optimal method to use is
highly architecture and platform dependent. For further details,
see the <a href="../misc/perf-tuning.html">performance tuning</a>
documentation.</p>
<p>If this directive is set to <code>default</code>, then the
compile-time selected default will be used. Other possible
methods are listed below. Note that not all methods are
available on all platforms. If a method is specified which is
not available, a message will be written to the error log
listing the available methods.</p>
<dl>
<dt><code>flock</code></dt>
<dd>uses the <code>flock(2)</code> system call to lock the
file defined by the <a href="mpm_common.html#lockfile" class="directive"><code class="directive">LockFile</code></a> directive.</dd>
<dt><code>fcntl</code></dt>
<dd>uses the <code>fnctl(2)</code> system call to lock the
file defined by the <a href="mpm_common.html#lockfile" class="directive"><code class="directive">LockFile</code></a> directive.</dd>
<dt><code>sysvsem</code></dt>
<dd>uses SySV-style semaphores to implement the mutex.</dd>
<dt><code>pthread</code></dt>
<dd>uses POSIX mutexes as implemented by the POSIX Threads
(PThreads) specification.</dd>
</dl>
<hr/><h2><a name="MaxSpareServers">MaxSpareServers</a> <a name="maxspareservers">Directive</a></h2><table cellpadding="1" cellspacing="0" border="0" bgcolor="#cccccc"><tr><td><table bgcolor="#ffffff"><tr><td nowrap="nowrap"><strong>Description: </strong></td><td>Maximum number of idle child server processes</td></tr><tr><td nowrap="nowrap"><a href="directive-dict.html#Syntax" class="help">Syntax:</a></td><td>MaxSpareServers <em>number</em><br></td></tr><tr><td nowrap="nowrap"><a href="directive-dict.html#Default" class="help">Default:</a></td><td><code>MaxSpareServers 10</code></td></tr><tr><td nowrap="nowrap"><a href="directive-dict.html#Context" class="help">Context:</a></td><td>server config</td></tr><tr><td nowrap="nowrap"><a href="directive-dict.html#Status" class="help">Status:</a></td><td>MPM</td></tr><tr><td nowrap="nowrap"><a href="directive-dict.html#Module" class="help">Module:</a></td><td>prefork</td></tr></table></td></tr></table>
<p>The <code class="directive">MaxSpareServers</code> directive sets the
desired maximum number of <em>idle</em> child server processes. An
idle process is one which is not handling a request. If there are
more than MaxSpareServers idle, then the parent process will kill
off the excess processes.</p>
<p>Tuning of this parameter should only be necessary on very
busy sites. Setting this parameter to a large number is almost
always a bad idea.</p>
<p><strong>See also </strong></p><ul><li><a href="#minspareservers" class="directive"><code class="directive">MinSpareServers</code></a></li><li><a href="mpm_common.html#startservers" class="directive"><code class="directive">StartServers</code></a></li></ul><hr/><h2><a name="MinSpareServers">MinSpareServers</a> <a name="minspareservers">Directive</a></h2><table cellpadding="1" cellspacing="0" border="0" bgcolor="#cccccc"><tr><td><table bgcolor="#ffffff"><tr><td nowrap="nowrap"><strong>Description: </strong></td><td>Minimum number of idle child server processes</td></tr><tr><td nowrap="nowrap"><a href="directive-dict.html#Syntax" class="help">Syntax:</a></td><td>MinSpareServers <em>number</em></td></tr><tr><td nowrap="nowrap"><a href="directive-dict.html#Default" class="help">Default:</a></td><td><code>MinSpareServers 5</code></td></tr><tr><td nowrap="nowrap"><a href="directive-dict.html#Context" class="help">Context:</a></td><td>server config</td></tr><tr><td nowrap="nowrap"><a href="directive-dict.html#Status" class="help">Status:</a></td><td>MPM</td></tr><tr><td nowrap="nowrap"><a href="directive-dict.html#Module" class="help">Module:</a></td><td>prefork</td></tr></table></td></tr></table>
<p>The <code class="directive">MinSpareServers</code> directive sets the
desired minimum number of <em>idle</em> child server processes. An
idle process is one which is not handling a request. If there are
fewer than MinSpareServers idle, then the parent process creates
new children at a maximum rate of 1 per second.</p>
<p>Tuning of this parameter should only be necessary on very
busy sites. Setting this parameter to a large number is almost
always a bad idea.</p>
<p><strong>See also </strong></p><ul><li><a href="#maxspareservers" class="directive"><code class="directive">MaxSpareServers</code></a></li><li><a href="mpm_common.html#startservers" class="directive"><code class="directive">StartServers</code></a></li></ul><hr/></blockquote><h3 align="center">Apache HTTP Server Version 2.0</h3><a href="./"><img src="../images/index.gif" alt="Index"/></a><a href="../"><img src="../images/home.gif" alt="Home"/></a></body></html>
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