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10 <title>Multi-Processing Modules (MPMs) - Apache HTTP Server Version 2.5</title>
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20 <p class="apache">Apache HTTP Server Version 2.5</p>
21 <img alt="" src="./images/feather.png" /></div>
22 <div class="up"><a href="./"><img title="<-" alt="<-" src="./images/left.gif" /></a></div>
24 <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 2.5</a></div><div id="page-content"><div id="preamble"><h1>Multi-Processing Modules (MPMs)</h1>
26 <p><span>Available Languages: </span><a href="./de/mpm.html" hreflang="de" rel="alternate" title="Deutsch"> de </a> |
27 <a href="./en/mpm.html" title="English"> en </a> |
28 <a href="./es/mpm.html" hreflang="es" rel="alternate" title="Español"> es </a> |
29 <a href="./fr/mpm.html" hreflang="fr" rel="alternate" title="Français"> fr </a> |
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33 <a href="./zh-cn/mpm.html" hreflang="zh-cn" rel="alternate" title="Simplified Chinese"> zh-cn </a></p>
36 <p>This document describes what a Multi-Processing Module is and
37 how they are used by the Apache HTTP Server.</p>
39 <div id="quickview"><ul id="toc"><li><img alt="" src="./images/down.gif" /> <a href="#introduction">Introduction</a></li>
40 <li><img alt="" src="./images/down.gif" /> <a href="#defaults">MPM Defaults</a></li>
41 <li><img alt="" src="./images/down.gif" /> <a href="#static">Building an MPM as a static module</a></li>
42 <li><img alt="" src="./images/down.gif" /> <a href="#dynamic">Building an MPM as a DSO module</a></li>
43 </ul><h3>See also</h3><ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div>
44 <div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
46 <h2><a name="introduction" id="introduction">Introduction</a></h2>
48 <p>The Apache HTTP Server is designed to be a powerful and
49 flexible web server that can work on a very wide variety of
50 platforms in a range of different environments. Different
51 platforms and different environments often require different
52 features, or may have different ways of implementing the same
53 feature most efficiently. Apache httpd has always accommodated a wide
54 variety of environments through its modular design. This design
55 allows the webmaster to choose which features will be included
56 in the server by selecting which modules to load either at
57 compile-time or at run-time.</p>
59 <p>Apache HTTP Server 2.0 extends this modular design to the most basic
60 functions of a web server. The server ships with a selection of
61 Multi-Processing Modules (MPMs) which are responsible for
62 binding to network ports on the machine, accepting requests,
63 and dispatching children to handle the requests.</p>
65 <p>Extending the modular design to this level of the server
66 allows two important benefits:</p>
69 <li>Apache httpd can more cleanly and efficiently support a wide
70 variety of operating systems. In particular, the Windows
71 version of the server is now much more efficient, since
72 <code class="module"><a href="./mod/mpm_winnt.html">mpm_winnt</a></code> can use native
73 networking features in place of the POSIX layer used in
74 Apache httpd 1.3. This benefit also extends to other operating
75 systems that implement specialized MPMs.</li>
77 <li>The server can be better customized for the needs of the
78 particular site. For example, sites that need a great deal of
79 scalability can choose to use a threaded MPM like
80 <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
81 stability or compatibility with older software can use a
82 <code class="module"><a href="./mod/prefork.html">prefork</a></code>.</li>
85 <p>At the user level, MPMs appear much like other Apache httpd
86 modules. The main difference is that one and only one MPM must
87 be loaded into the server at any time. The list of available
88 MPMs appears on the <a href="mod/">module index page</a>.</p>
90 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
92 <h2><a name="defaults" id="defaults">MPM Defaults</a></h2>
94 <p>The following table lists the default MPMs for various operating
95 systems. This will be the MPM selected if you do not make another
96 choice at compile-time.</p>
98 <table class="bordered"><tr><td>Netware</td><td><code class="module"><a href="./mod/mpm_netware.html">mpm_netware</a></code></td></tr>
99 <tr class="odd"><td>OS/2</td><td><code class="module"><a href="./mod/mpmt_os2.html">mpmt_os2</a></code></td></tr>
100 <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
101 <code class="module"><a href="./mod/event.html">event</a></code>, depending on platform capabilities</td></tr>
102 <tr class="odd"><td>Windows</td><td><code class="module"><a href="./mod/mpm_winnt.html">mpm_winnt</a></code></td></tr>
105 <div class="note"><p>Here, 'Unix' is used to mean Unix-like operating systems, such as
106 Linux, BSD, Solaris, Mac OS X, etc.</p></div>
108 <p>In the case of Unix, the decision as to which MPM is installed is
109 based on two questions:</p>
110 <p>1. Does the system support threads?</p>
111 <p>2. Does the system support thread-safe polling (Specifically, the
112 kqueue and epoll functions)?</p>
114 <p>If the answer to both questions is 'yes', the default MPM is
115 <code class="module"><a href="./mod/event.html">event</a></code>.</p>
117 <p>If The answer to #1 is 'yes', but the answer to #2 is 'no', the
118 default will be <code class="module"><a href="./mod/worker.html">worker</a></code>.</p>
120 <p>If the answer to both questions is 'no', then the default MPM will be
121 <code class="module"><a href="./mod/prefork.html">prefork</a></code>.</p>
123 <p>In practical terms, this means that the default will almost always be
124 <code class="module"><a href="./mod/event.html">event</a></code>, as all modern operating systems support these
127 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
128 <div class="section">
129 <h2><a name="static" id="static">Building an MPM as a static module</a></h2>
131 <p>MPMs can be built as static modules on all platforms. A single MPM
132 is chosen at build time and linked into the server. The server must
133 be rebuilt in order to change the MPM.</p>
135 <p>To override the default MPM choice, use the
136 <code>--with-mpm=<em>NAME</em></code> option of the
137 <code class="program"><a href="./programs/configure.html">configure</a></code> script. <em>NAME</em> is the name of the
140 <p>Once the server has been compiled, it is possible to determine which MPM
141 was chosen by using <code>./httpd -l</code>. This command will list every
142 module that is compiled into the server, including the MPM.</p>
144 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
145 <div class="section">
146 <h2><a name="dynamic" id="dynamic">Building an MPM as a DSO module</a></h2>
148 <p>On Unix and similar platforms, MPMs can be built as DSO modules and
149 dynamically loaded into the server in the same manner as other DSO
150 modules. Building MPMs as DSO modules allows the MPM to be changed by
151 updating the <code class="directive"><a href="./mod/mod_so.html#loadmodule">LoadModule</a></code> directive
152 for the MPM instead of by rebuilding the server.</p>
154 <pre class="prettyprint lang-config">LoadModule mpm_prefork_module modules/mod_mpm_prefork.so</pre>
157 <p>Attempting to <code class="directive"><a href="./mod/mod_so.html#loadmodule">LoadModule</a></code>
158 more than one MPM will result in a startup failure with the
161 <div class="example"><p><code>AH00534: httpd: Configuration error: More than one MPM
162 loaded.</code></p></div>
164 <p>This feature is enabled using the
165 <code>--enable-mpms-shared</code> option of the <code class="program"><a href="./programs/configure.html">configure</a></code>
167 With argument <code><em>all</em></code>, all possible MPMs for the platform
168 will be installed. Alternately, a list of MPMs can be specified as the
171 <p>The default MPM, either selected automatically or specified with the
172 <code>--with-mpm</code> option of the <code class="program"><a href="./programs/configure.html">configure</a></code>
173 script, will be loaded in the generated server configuration file. Edit the
174 <code class="directive"><a href="./mod/mod_so.html#loadmodule">LoadModule</a></code> directive to select a
178 <div class="bottomlang">
179 <p><span>Available Languages: </span><a href="./de/mpm.html" hreflang="de" rel="alternate" title="Deutsch"> de </a> |
180 <a href="./en/mpm.html" title="English"> en </a> |
181 <a href="./es/mpm.html" hreflang="es" rel="alternate" title="Español"> es </a> |
182 <a href="./fr/mpm.html" hreflang="fr" rel="alternate" title="Français"> fr </a> |
183 <a href="./ja/mpm.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
184 <a href="./ko/mpm.html" hreflang="ko" rel="alternate" title="Korean"> ko </a> |
185 <a href="./tr/mpm.html" hreflang="tr" rel="alternate" title="Türkçe"> tr </a> |
186 <a href="./zh-cn/mpm.html" hreflang="zh-cn" rel="alternate" title="Simplified Chinese"> zh-cn </a></p>
187 </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&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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