prefork.xml revision fc88db23cb4b205f1efea5f5d5ae916589db5a61
<?xml version="1.0"?>
<modulesynopsis>
<name>prefork</name>
<description>Implements a non-threaded, pre-forking web server</description>
<status>MPM</status>
<identifier>mpm_prefork_module</identifier>
<summary>
<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 <directive module="mpm_common">StartServers</directive>,
<directive module="prefork">MinSpareServers</directive>,
<directive module="prefork">MaxSpareServers</directive>, and
<directive module="mpm_common">MaxClients</directive> 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 <directive module="mpm_common">MaxClients</directive>,
while sites with limited memory may need to decrease <directive
module="mpm_common">MaxClients</directive> 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 <directive
module="mpm_common">User</directive> and <directive
module="mpm_common">Group</directive> 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
these directives also set the privileges which will be inherited
by CGI scripts.</p>
<p><directive module="mpm_common">MaxRequestsPerChild</directive>
controls how frequently the server recycles processes by killing
old ones and launching new ones.</p>
</summary>
ports Apache uses</a></seealso>
<directivesynopsis location="mpm_common">
<name>CoreDumpDirectory</name>
</directivesynopsis>
<directivesynopsis location="mpm_common">
<name>PidFile</name>
</directivesynopsis>
<directivesynopsis location="mpm_common">
<name>Listen</name>
</directivesynopsis>
<directivesynopsis location="mpm_common">
<name>ListenBacklog</name>
</directivesynopsis>
<directivesynopsis location="mpm_common">
<name>LockFile</name>
</directivesynopsis>
<directivesynopsis location="mpm_common">
<name>MaxRequestsPerChild</name>
</directivesynopsis>
<directivesynopsis location="mpm_common">
<name>MaxSpareServers</name>
</directivesynopsis>
<directivesynopsis location="mpm_common">
<name>MinSpareServers</name>
</directivesynopsis>
<directivesynopsis location="mpm_common">
<name>ScoreBoardFile</name>
</directivesynopsis>
<directivesynopsis location="mpm_common">
<name>SendBufferSize</name>
</directivesynopsis>
<directivesynopsis location="mpm_common">
<name>ServerLimit</name>
</directivesynopsis>
<directivesynopsis location="mpm_common">
<name>StartServers</name>
</directivesynopsis>
<directivesynopsis location="mpm_common">
<name>User</name>
</directivesynopsis>
<directivesynopsis>
<name>AcceptMutex</name>
<description>Method that Apache uses to serialize multiple children
accepting requests on network sockets</description>
<syntax>AcceptMutex default|<em>method</em></syntax>
<default>AcceptMutex default</default>
<contextlist><context>server config</context></contextlist>
<usage>
<p>The <directive>AcceptMutex</directive> 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,
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 <directive module="mpm_common"
>LockFile</directive> directive.</dd>
<dt><code>fcntl</code></dt>
<dd>uses the <code>fnctl(2)</code> system call to lock the
file defined by the <directive module="mpm_common"
>LockFile</directive> 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>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>MaxSpareServers</name>
<description>Maximum number of idle child server processes</description>
<syntax>MaxSpareServers <em>number</em><br /></syntax>
<default>MaxSpareServers 10</default>
<contextlist><context>server config</context></contextlist>
<usage>
<p>The <directive>MaxSpareServers</directive> 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>
</usage>
<seealso><directive module="prefork">MinSpareServers</directive></seealso>
<seealso><directive module="mpm_common">StartServers</directive></seealso>
</directivesynopsis>
<directivesynopsis>
<name>MinSpareServers</name>
<description>Minimum number of idle child server processes</description>
<syntax>MinSpareServers <em>number</em></syntax>
<default>MinSpareServers 5</default>
<contextlist><context>server config</context></contextlist>
<usage>
<p>The <directive>MinSpareServers</directive> 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>
</usage>
<seealso><directive module="prefork">MaxSpareServers</directive></seealso>
<seealso><directive module="mpm_common">StartServers</directive></seealso>
</directivesynopsis>
</modulesynopsis>