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f052a448696b1246ee9fc36b7c727237aed56058Timo Sirainen <title>Apache MPM prefork</title>
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f052a448696b1246ee9fc36b7c727237aed56058Timo Sirainen <h1 align="CENTER">Multi-Processing Module prefork</h1>
f052a448696b1246ee9fc36b7c727237aed56058Timo Sirainen
f052a448696b1246ee9fc36b7c727237aed56058Timo Sirainen <p>This Multi-Processing Module implements a non-threaded,
f052a448696b1246ee9fc36b7c727237aed56058Timo Sirainen pre-forking web server.</p>
f052a448696b1246ee9fc36b7c727237aed56058Timo Sirainen
f052a448696b1246ee9fc36b7c727237aed56058Timo Sirainen <p><a href="module-dict.html#Status"
f052a448696b1246ee9fc36b7c727237aed56058Timo Sirainen rel="Help"><strong>Status:</strong></a> MPM<br />
f052a448696b1246ee9fc36b7c727237aed56058Timo Sirainen <a href="module-dict.html#SourceFile"
f052a448696b1246ee9fc36b7c727237aed56058Timo Sirainen 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>MaxClients</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="#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#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#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>
<hr />
<h2><a id="AcceptMutex" name="AcceptMutex">AcceptMutex
Directive</a></h2>
<p><a href="directive-dict.html#Syntax"
rel="Help"><strong>Syntax:</strong></a> AcceptMutex
default|<em>method</em><br />
<a href="directive-dict.html#Default"
rel="Help"><strong>Default:</strong></a> <code>AcceptMutex
default</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>
<p>The <code>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">LockFile</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">LockFile</a> directive.</dd>
<dt><code>sysvsem</code></dt>
<dd>uses SySV-style semaphores to implement the mutex.</dd>
<dt><code>proc_pthread</code></dt>
<dd>uses POSIX mutexes as implemented by the POSIX Threads
(PThreads) specification.</dd>
</dl>
<hr />
<h2><a id="maxspareservers"
name="maxspareservers">MaxSpareServers directive</a></h2>
<!--%plaintext &lt;?INDEX {\tt MaxSpareServers} directive&gt; -->
<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>
<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 id="minspareservers"
name="minspareservers">MinSpareServers directive</a></h2>
<!--%plaintext &lt;?INDEX {\tt MinSpareServers} directive&gt; -->
<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>
<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>This directive has no effect on Microsoft Windows.</p>
<p>See also <a href="#maxspareservers">MaxSpareServers</a> and
<a href="mpm_common.html#startservers">StartServers</a>.
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