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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
<HTML>
<HEAD>
<TITLE>Apache MPM prefork</TITLE>
</HEAD>
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<H1 ALIGN="CENTER">Multi-Processing Module prefork</H1>
<P>
This Multi-Processing Module implements a non-threaded, pre-forking
web server.
</P>
<P><A
HREF="module-dict.html#Status"
REL="Help"
><STRONG>Status:</STRONG></A> MPM
<BR>
<A
HREF="module-dict.html#SourceFile"
REL="Help"
><STRONG>Source File:</STRONG></A> prefork.c
<BR>
<A
HREF="module-dict.html#ModuleIdentifier"
REL="Help"
><STRONG>Module Identifier:</STRONG></A> mpm_prefork_module
</P>
<H2>Summary</H2>
<p>This Multi-Processing Module (MPM) implements a non-threaded,
pre-forking web server which handles request in a manner very similar
to the default behavior of Apache 1.3 on Unix.</p>
<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 <code>StartServers</code>, <code>MinSpareServers</code>,
<code>MaxSpareServers</code>, and <code>MaxServers</code> 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
<code>MaxClients</code>, while sites with limited memory may need to
decrease <code>MaxClients</code> 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 <code>User</code> and
<code>Group</code> 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.
In addition, unless <a href="../suexec.html">suexec</a> is used,
these directives also set the privileges which will be inherited
by CGI scripts.</p>
<p><code>MaxRequestsPerChild</code> controls how frequently the server
recycles processes by killing old ones and launching new ones.</p>
<p>See also: <a href="../bind.html">Setting which addresses and ports
Apache uses</a>.</p>
<H2>Directives</H2>
<UL>
<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#pidfile">PidFile</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="#maxspareservers">MaxSpareServers</a></li>
<li><a href="#minspareservers">MinSpareServers</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#startservers">StartServers</a></li>
<li><a href="mpm_common.html#user">User</a></li>
</UL>
<p><hr>
<H2><A NAME="maxspareservers">MaxSpareServers directive</A></H2>
<!--%plaintext <?INDEX {\tt MaxSpareServers} directive> -->
<A
HREF="directive-dict.html#Syntax"
REL="Help"
><STRONG>Syntax:</STRONG></A> MaxSpareServers <EM>number</EM><BR>
<A
HREF="directive-dict.html#Default"
REL="Help"
><STRONG>Default:</STRONG></A> <CODE>MaxSpareServers 10</CODE><BR>
<A
HREF="directive-dict.html#Context"
REL="Help"
><STRONG>Context:</STRONG></A> server config<BR>
<A
HREF="directive-dict.html#Status"
REL="Help"
><STRONG>Status:</STRONG></A> core<P>
The MaxSpareServers 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>
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>
See also <A HREF="#minspareservers">MinSpareServers</A> and
<A HREF="mpm_common.html#startservers">StartServers</A>.<P><HR>
<H2><A NAME="minspareservers">MinSpareServers directive</A></H2>
<!--%plaintext <?INDEX {\tt MinSpareServers} directive> -->
<A
HREF="directive-dict.html#Syntax"
REL="Help"
><STRONG>Syntax:</STRONG></A> MinSpareServers <EM>number</EM><BR>
<A
HREF="directive-dict.html#Default"
REL="Help"
><STRONG>Default:</STRONG></A> <CODE>MinSpareServers 5</CODE><BR>
<A
HREF="directive-dict.html#Context"
REL="Help"
><STRONG>Context:</STRONG></A> server config<BR>
<A
HREF="directive-dict.html#Status"
REL="Help"
><STRONG>Status:</STRONG></A> core<P>
The MinSpareServers 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>
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>
This directive has no effect on Microsoft Windows.
<P>
See also <A HREF="#maxspareservers">MaxSpareServers</A> and
<A HREF="mpm_common.html#startservers">StartServers</A>.
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