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<title>Multi-Processing Modules (MPMs) - Apache HTTP Server Version 2.4</title>
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<body id="manual-page">
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Modules | Directives | FAQ | Glossary | Sitemap
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Apache HTTP Server Version 2.4
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Apache > HTTP Server > Documentation > Version 2.4Multi-Processing Modules (MPMs)
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Available Languages: de |
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en |
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This document describes what a Multi-Processing Module is and
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how they are used by the Apache HTTP Server.
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 MPM Defaults
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Building an MPM as a static module
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Building an MPM as a DSO module
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See also
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The Apache HTTP Server is designed to be a powerful and
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flexible web server that can work on a very wide variety of
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platforms in a range of different environments. Different
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platforms and different environments often require different
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features, or may have different ways of implementing the same
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feature most efficiently. Apache httpd has always accommodated a wide
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variety of environments through its modular design. This design
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allows the webmaster to choose which features will be included
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in the server by selecting which modules to load either at
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compile-time or at run-time.
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Apache HTTP Server 2.0 extends this modular design to the most basic
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functions of a web server. The server ships with a selection of
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Multi-Processing Modules (MPMs) which are responsible for
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binding to network ports on the machine, accepting requests,
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and dispatching children to handle the requests.
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Extending the modular design to this level of the server
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allows two important benefits:
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Apache httpd can more cleanly and efficiently support a wide
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variety of operating systems. In particular, the Windows
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version of the server is now much more efficient, since
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mpm_winnt can use native
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networking features in place of the POSIX layer used in
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Apache httpd 1.3. This benefit also extends to other operating
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systems that implement specialized MPMs.
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The server can be better customized for the needs of the
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particular site. For example, sites that need a great deal of
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scalability can choose to use a threaded MPM like
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worker or event, while sites requiring
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stability or compatibility with older software can use a
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prefork.
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At the user level, MPMs appear much like other Apache httpd
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modules. The main difference is that one and only one MPM must
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be loaded into the server at any time. The list of available
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MPMs appears on the module index page.
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The following table lists the default MPMs for various operating
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systems. This will be the MPM selected if you do not make another
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choice at compile-time.
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OS/2mpmt_os2
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Unixprefork, worker, or
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event, depending on platform capabilities
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Windowsmpm_winnt
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Here, 'Unix' is used to mean Unix-like operating systems, such as
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Linux, BSD, Solaris, Mac OS X, etc.
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In the case of Unix, the decision as to which MPM is installed is
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based on two questions:
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1. Does the system support threads?
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2. Does the system support thread-safe polling (Specifically, the
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kqueue and epoll functions)?
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If the answer to both questions is 'yes', the default MPM is
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event.
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If The answer to #1 is 'yes', but the answer to #2 is 'no', the
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default will be worker.
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If the answer to both questions is 'no', then the default MPM will be
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prefork.
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In practical terms, this means that the default will almost always be
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event, as all modern operating systems support these
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two features.
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MPMs can be built as static modules on all platforms. A single MPM
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is chosen at build time and linked into the server. The server must
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be rebuilt in order to change the MPM.
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To override the default MPM choice, use the
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--with-mpm=NAME option of the
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configure script. NAME is the name of the
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desired MPM.
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Once the server has been compiled, it is possible to determine which MPM
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was chosen by using ./httpd -l. This command will list every
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module that is compiled into the server, including the MPM.
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On Unix and similar platforms, MPMs can be built as DSO modules and
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dynamically loaded into the server in the same manner as other DSO
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modules. Building MPMs as DSO modules allows the MPM to be changed by
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updating the LoadModule directive
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for the MPM instead of by rebuilding the server.
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LoadModule mpm_prefork_module modules/mod_mpm_prefork.so
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Attempting to LoadModule
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more than one MPM will result in a startup failure with the
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following error.
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AH00534: httpd: Configuration error: More than one MPM
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loaded.
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This feature is enabled using the
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--enable-mpms-shared option of the configure
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script.
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With argument all, all possible MPMs for the platform
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will be installed. Alternately, a list of MPMs can be specified as the
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argument.
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The default MPM, either selected automatically or specified with the
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--with-mpm option of the configure
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script, will be loaded in the generated server configuration file. Edit the
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LoadModule directive to select a
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different MPM.
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Available Languages: de |
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en |
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es |
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fr |
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zh-cn
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Notice: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 mailing lists.
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