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8 <title>Multi-Processing Modules (MPMs) - Apache HTTP Server</title>
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15 <p class="apache">Apache HTTP Server Version 2.3</p>
16 <img alt="" src="./images/feather.gif" /></div>
17 <div class="up"><a href="./"><img title="<-" alt="<-" src="./images/left.gif" /></a></div>
19 <a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="./">Version 2.3</a></div><div id="page-content"><div id="preamble"><h1>Multi-Processing Modules (MPMs)</h1>
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30 <p>This document describes what a Multi-Processing Module is and
31 how they are used by the Apache HTTP Server.</p>
33 <div id="quickview"><ul id="toc"><li><img alt="" src="./images/down.gif" /> <a href="#introduction">Introduction</a></li>
34 <li><img alt="" src="./images/down.gif" /> <a href="#defaults">MPM Defaults</a></li>
35 <li><img alt="" src="./images/down.gif" /> <a href="#static">Building an MPM as a static module</a></li>
36 <li><img alt="" src="./images/down.gif" /> <a href="#dynamic">Building an MPM as a DSO module</a></li>
38 <div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
40 <h2><a name="introduction" id="introduction">Introduction</a></h2>
42 <p>The Apache HTTP Server is designed to be a powerful and
43 flexible web server that can work on a very wide variety of
44 platforms in a range of different environments. Different
45 platforms and different environments often require different
46 features, or may have different ways of implementing the same
47 feature most efficiently. Apache httpd has always accommodated a wide
48 variety of environments through its modular design. This design
49 allows the webmaster to choose which features will be included
50 in the server by selecting which modules to load either at
51 compile-time or at run-time.</p>
53 <p>Apache HTTP Server 2.0 extends this modular design to the most basic
54 functions of a web server. The server ships with a selection of
55 Multi-Processing Modules (MPMs) which are responsible for
56 binding to network ports on the machine, accepting requests,
57 and dispatching children to handle the requests.</p>
59 <p>Extending the modular design to this level of the server
60 allows two important benefits:</p>
63 <li>Apache httpd can more cleanly and efficiently support a wide
64 variety of operating systems. In particular, the Windows
65 version of the server is now much more efficient, since
66 <code class="module"><a href="./mod/mpm_winnt.html">mpm_winnt</a></code> can use native
67 networking features in place of the POSIX layer used in
68 Apache httpd 1.3. This benefit also extends to other operating
69 systems that implement specialized MPMs.</li>
71 <li>The server can be better customized for the needs of the
72 particular site. For example, sites that need a great deal of
73 scalability can choose to use a threaded MPM like
74 <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
75 stability or compatibility with older software can use a
76 <code class="module"><a href="./mod/prefork.html">prefork</a></code>.</li>
79 <p>At the user level, MPMs appear much like other Apache httpd
80 modules. The main difference is that one and only one MPM must
81 be loaded into the server at any time. The list of available
82 MPMs appears on the <a href="mod/">module index page</a>.</p>
84 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
86 <h2><a name="defaults" id="defaults">MPM Defaults</a></h2>
88 <p>The following table lists the default MPMs for various operating
89 systems. This will be the MPM selected if you do not make another
90 choice at compile-time.</p>
92 <table class="bordered"><tr><td>Netware</td><td><code class="module"><a href="./mod/mpm_netware.html">mpm_netware</a></code></td></tr>
93 <tr class="odd"><td>OS/2</td><td><code class="module"><a href="./mod/mpmt_os2.html">mpmt_os2</a></code></td></tr>
94 <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
95 <code class="module"><a href="./mod/event.html">event</a></code>, depending on platform capabilities</td></tr>
96 <tr class="odd"><td>Windows</td><td><code class="module"><a href="./mod/mpm_winnt.html">mpm_winnt</a></code></td></tr>
98 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
100 <h2><a name="static" id="static">Building an MPM as a static module</a></h2>
102 <p>MPMs can be built as static modules on all platforms. A single MPM
103 is chosen at build time and linked into the server. The server must
104 be rebuilt in order to change the MPM.</p>
106 <p>To override the default MPM choice, use the
107 <code>--with-mpm=<em>NAME</em></code> option of the
108 <code class="program"><a href="./programs/configure.html">configure</a></code> script. <em>NAME</em> is the name of the
111 <p>Once the server has been compiled, it is possible to determine which MPM
112 was chosen by using <code>./httpd -l</code>. This command will list every
113 module that is compiled into the server, including the MPM.</p>
115 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
116 <div class="section">
117 <h2><a name="dynamic" id="dynamic">Building an MPM as a DSO module</a></h2>
119 <p>On Unix and similar platforms, MPMs can be built as DSO modules and
120 dynamically loaded into the server in the same manner as other DSO
121 modules. Building MPMs as DSO modules allows the MPM to be changed by
122 updating the <code class="directive"><a href="./mod/mod_so.html#loadmodule">LoadModule</a></code> directive
123 for the MPM instead of by rebuilding the server.</p>
125 <p>This feature is enabled using the
126 <code>--enable-mpms-shared</code> option of the <code class="program"><a href="./programs/configure.html">configure</a></code>
128 With argument <code><em>all</em></code>, all possible MPMs for the platform
129 will be installed. Alternately, a list of MPMs can be specified as the
132 <p>The default MPM, either selected automatically or specified with the
133 <code>--with-mpm</code> option of the <code class="program"><a href="./programs/configure.html">configure</a></code>
134 script, will be loaded in the generated server configuration file. Edit the
135 <code class="directive"><a href="./mod/mod_so.html#loadmodule">LoadModule</a></code> directive to select a
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