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+<title>Multi-Processing Modules (MPMs) - Apache HTTP Server Version 2.4</title>
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+<body id="manual-page"><div id="page-header">
+<p class="menu"><a href="./mod/">Modules</a> | <a href="./mod/directives.html">Directives</a> | <a href="http://wiki.apache.org/httpd/FAQ">FAQ</a> | <a href="./glossary.html">Glossary</a> | <a href="./sitemap.html">Sitemap</a></p>
+<p class="apache">Apache HTTP Server Version 2.4</p>
+<img alt="" src="./images/feather.png" /></div>
+<div class="up"><a href="./"><img title="&lt;-" alt="&lt;-" src="./images/left.gif" /></a></div>
+<div id="path">
+<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/">Documentation</a> &gt; <a href="./">Version 2.4</a></div><div id="page-content"><div id="preamble"><h1>Multi-Processing Modules (MPMs)</h1>
+<div class="toplang">
+<p><span>Available Languages: </span><a href="./de/mpm.html" hreflang="de" rel="alternate" title="Deutsch">&nbsp;de&nbsp;</a> |
+<a href="./en/mpm.html" title="English">&nbsp;en&nbsp;</a> |
+<a href="./es/mpm.html" hreflang="es" rel="alternate" title="Español">&nbsp;es&nbsp;</a> |
+<a href="./fr/mpm.html" hreflang="fr" rel="alternate" title="Français">&nbsp;fr&nbsp;</a> |
+<a href="./ja/mpm.html" hreflang="ja" rel="alternate" title="Japanese">&nbsp;ja&nbsp;</a> |
+<a href="./ko/mpm.html" hreflang="ko" rel="alternate" title="Korean">&nbsp;ko&nbsp;</a> |
+<a href="./tr/mpm.html" hreflang="tr" rel="alternate" title="Türkçe">&nbsp;tr&nbsp;</a> |
+<a href="./zh-cn/mpm.html" hreflang="zh-cn" rel="alternate" title="Simplified Chinese">&nbsp;zh-cn&nbsp;</a></p>
+</div>
+
+<p>This document describes what a Multi-Processing Module is and
+how they are used by the Apache HTTP Server.</p>
+</div>
+<div id="quickview"><a href="https://www.apache.org/foundation/contributing.html" class="badge"><img src="https://www.apache.org/images/SupportApache-small.png" alt="Support Apache!" /></a><ul id="toc"><li><img alt="" src="./images/down.gif" /> <a href="#introduction">Introduction</a></li>
+<li><img alt="" src="./images/down.gif" /> <a href="#defaults">MPM Defaults</a></li>
+<li><img alt="" src="./images/down.gif" /> <a href="#static">Building an MPM as a static module</a></li>
+<li><img alt="" src="./images/down.gif" /> <a href="#dynamic">Building an MPM as a DSO module</a></li>
+</ul><h3>See also</h3><ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div>
+<div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
+<div class="section">
+<h2><a name="introduction" id="introduction">Introduction</a></h2>
+
+ <p>The Apache HTTP Server is designed to be a powerful and
+ flexible web server that can work on a very wide variety of
+ platforms in a range of different environments. Different
+ platforms and different environments often require different
+ features, or may have different ways of implementing the same
+ feature most efficiently. Apache httpd has always accommodated a wide
+ variety of environments through its modular design. This design
+ allows the webmaster to choose which features will be included
+ in the server by selecting which modules to load either at
+ compile-time or at run-time.</p>
+
+ <p>Apache HTTP Server 2.0 extends this modular design to the most basic
+ functions of a web server. The server ships with a selection of
+ Multi-Processing Modules (MPMs) which are responsible for
+ binding to network ports on the machine, accepting requests,
+ and dispatching children to handle the requests.</p>
+
+ <p>Extending the modular design to this level of the server
+ allows two important benefits:</p>
+
+ <ul>
+ <li>Apache httpd can more cleanly and efficiently support a wide
+ variety of operating systems. In particular, the Windows
+ version of the server is now much more efficient, since
+ <code class="module"><a href="./mod/mpm_winnt.html">mpm_winnt</a></code> can use native
+ networking features in place of the POSIX layer used in
+ Apache httpd 1.3. This benefit also extends to other operating
+ systems that implement specialized MPMs.</li>
+
+ <li>The server can be better customized for the needs of the
+ particular site. For example, sites that need a great deal of
+ scalability can choose to use a threaded MPM like
+ <code class="module"><a href="./mod/worker.html">worker</a></code> or <code class="module"><a href="./mod/event.html">event</a></code>, while sites requiring
+ stability or compatibility with older software can use a
+ <code class="module"><a href="./mod/prefork.html">prefork</a></code>.</li>
+ </ul>
+
+ <p>At the user level, MPMs appear much like other Apache httpd
+ modules. The main difference is that one and only one MPM must
+ be loaded into the server at any time. The list of available
+ MPMs appears on the <a href="mod/">module index page</a>.</p>
+
+</div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
+<div class="section">
+<h2><a name="defaults" id="defaults">MPM Defaults</a></h2>
+
+<p>The following table lists the default MPMs for various operating
+systems. This will be the MPM selected if you do not make another
+choice at compile-time.</p>
+
+<table class="bordered"><tr><td>Netware</td><td><code class="module"><a href="./mod/mpm_netware.html">mpm_netware</a></code></td></tr>
+<tr class="odd"><td>OS/2</td><td><code class="module"><a href="./mod/mpmt_os2.html">mpmt_os2</a></code></td></tr>
+<tr><td>Unix</td><td><code class="module"><a href="./mod/prefork.html">prefork</a></code>, <code class="module"><a href="./mod/worker.html">worker</a></code>, or
+ <code class="module"><a href="./mod/event.html">event</a></code>, depending on platform capabilities</td></tr>
+<tr class="odd"><td>Windows</td><td><code class="module"><a href="./mod/mpm_winnt.html">mpm_winnt</a></code></td></tr>
+</table>
+
+<div class="note"><p>Here, 'Unix' is used to mean Unix-like operating systems, such as
+Linux, BSD, Solaris, Mac OS X, etc.</p></div>
+
+<p>In the case of Unix, the decision as to which MPM is installed is
+based on two questions:</p>
+<p>1. Does the system support threads?</p>
+<p>2. Does the system support thread-safe polling (Specifically, the
+kqueue and epoll functions)?</p>
+
+<p>If the answer to both questions is 'yes', the default MPM is
+<code class="module"><a href="./mod/event.html">event</a></code>.</p>
+
+<p>If The answer to #1 is 'yes', but the answer to #2 is 'no', the
+default will be <code class="module"><a href="./mod/worker.html">worker</a></code>.</p>
+
+<p>If the answer to both questions is 'no', then the default MPM will be
+<code class="module"><a href="./mod/prefork.html">prefork</a></code>.</p>
+
+<p>In practical terms, this means that the default will almost always be
+<code class="module"><a href="./mod/event.html">event</a></code>, as all modern operating systems support these
+two features.</p>
+
+</div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
+<div class="section">
+<h2><a name="static" id="static">Building an MPM as a static module</a></h2>
+
+ <p>MPMs can be built as static modules on all platforms. A single MPM
+ is chosen at build time and linked into the server. The server must
+ be rebuilt in order to change the MPM.</p>
+
+ <p>To override the default MPM choice, use the
+ <code>--with-mpm=<em>NAME</em></code> option of the
+ <code class="program"><a href="./programs/configure.html">configure</a></code> script. <em>NAME</em> is the name of the
+ desired MPM.</p>
+
+ <p>Once the server has been compiled, it is possible to determine which MPM
+ was chosen by using <code>./httpd -l</code>. This command will list every
+ module that is compiled into the server, including the MPM.</p>
+
+</div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
+<div class="section">
+<h2><a name="dynamic" id="dynamic">Building an MPM as a DSO module</a></h2>
+
+ <p>On Unix and similar platforms, MPMs can be built as DSO modules and
+ dynamically loaded into the server in the same manner as other DSO
+ modules. Building MPMs as DSO modules allows the MPM to be changed by
+ updating the <code class="directive"><a href="./mod/mod_so.html#loadmodule">LoadModule</a></code> directive
+ for the MPM instead of by rebuilding the server.</p>
+
+ <pre class="prettyprint lang-config">LoadModule mpm_prefork_module modules/mod_mpm_prefork.so</pre>
+
+
+ <p>Attempting to <code class="directive"><a href="./mod/mod_so.html#loadmodule">LoadModule</a></code>
+ more than one MPM will result in a startup failure with the
+ following error.</p>
+
+ <div class="example"><p><code>AH00534: httpd: Configuration error: More than one MPM
+ loaded.</code></p></div>
+
+ <p>This feature is enabled using the
+ <code>--enable-mpms-shared</code> option of the <code class="program"><a href="./programs/configure.html">configure</a></code>
+ script.
+ With argument <code><em>all</em></code>, all possible MPMs for the platform
+ will be installed. Alternately, a list of MPMs can be specified as the
+ argument.</p>
+
+ <p>The default MPM, either selected automatically or specified with the
+ <code>--with-mpm</code> option of the <code class="program"><a href="./programs/configure.html">configure</a></code>
+ script, will be loaded in the generated server configuration file. Edit the
+ <code class="directive"><a href="./mod/mod_so.html#loadmodule">LoadModule</a></code> directive to select a
+ different MPM.</p>
+
+</div></div>
+<div class="bottomlang">
+<p><span>Available Languages: </span><a href="./de/mpm.html" hreflang="de" rel="alternate" title="Deutsch">&nbsp;de&nbsp;</a> |
+<a href="./en/mpm.html" title="English">&nbsp;en&nbsp;</a> |
+<a href="./es/mpm.html" hreflang="es" rel="alternate" title="Español">&nbsp;es&nbsp;</a> |
+<a href="./fr/mpm.html" hreflang="fr" rel="alternate" title="Français">&nbsp;fr&nbsp;</a> |
+<a href="./ja/mpm.html" hreflang="ja" rel="alternate" title="Japanese">&nbsp;ja&nbsp;</a> |
+<a href="./ko/mpm.html" hreflang="ko" rel="alternate" title="Korean">&nbsp;ko&nbsp;</a> |
+<a href="./tr/mpm.html" hreflang="tr" rel="alternate" title="Türkçe">&nbsp;tr&nbsp;</a> |
+<a href="./zh-cn/mpm.html" hreflang="zh-cn" rel="alternate" title="Simplified Chinese">&nbsp;zh-cn&nbsp;</a></p>
+</div><div class="top"><a href="#page-header"><img src="./images/up.gif" alt="top" /></a></div><div class="section"><h2><a id="comments_section" name="comments_section">Comments</a></h2><div class="warning"><strong>Notice:</strong><br />This is not a Q&amp;A section. Comments placed here should be pointed towards suggestions on improving the documentation or server, and may be removed again by our moderators if they are either implemented or considered invalid/off-topic. Questions on how to manage the Apache HTTP Server should be directed at either our IRC channel, #httpd, on Freenode, or sent to our <a href="http://httpd.apache.org/lists.html">mailing lists</a>.</div>
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