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Obtained from: Sander Striker git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@96782 13f79535-47bb-0310-9956-ffa450edef68
135 lines
14 KiB
XML
135 lines
14 KiB
XML
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XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
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--><title>prefork - Apache HTTP Server</title><link href="../style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" /><link href="../style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" /><link href="../style/css/manual-print.css" rel="stylesheet" media="print" type="text/css" /><link href="../images/favicon.ico" rel="shortcut icon" /></head><body><div id="page-header"><p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p><p class="apache">Apache HTTP Server Version 2.0</p><img alt="" src="../images/feather.gif" /></div><div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div><div id="path"><a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs-project/">Documentation</a> > <a href="../">Version 2.0</a> > <a href="./">Modules</a></div><div id="page-content"><div id="preamble"><h1>Apache Module prefork</h1><table class="module"><tr><th><a href="module-dict.html#Description">Description:
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</a></th><td>Implements a non-threaded, pre-forking web server</td></tr><tr><th><a href="module-dict.html#Status">Status:
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</a></th><td>MPM</td></tr><tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:
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</a></th><td>mpm_prefork_module</td></tr><tr><th><a href="module-dict.html#SourceFile">Source File:
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</a></th><td>prefork.c</td></tr></table><h3>Summary</h3>
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<p>This Multi-Processing Module (MPM) implements a non-threaded,
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pre-forking web server that handles requests in a manner similar
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to Apache 1.3. It is appropriate for sites that need to avoid
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threading for compatibility with non-thread-safe libraries. It
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is also the best MPM for isolating each request, so that a problem
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with a single request will not affect any other.</p>
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<p>This MPM is very self-regulating, so it is rarely necessary to
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adjust its configuration directives. Most important is that
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<code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code> be big enough to
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handle as many simultaneous requests as you expect to receive, but
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small enough to assure that there is enough physical RAM for all
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processes.</p>
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</div><div id="quickview"><h3 class="directives">Directives</h3><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#acceptmutex">AcceptMutex</a></li><li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#coredumpdirectory">CoreDumpDirectory</a></li><li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#group">Group</a></li><li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listen">Listen</a></li><li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listenbacklog">ListenBacklog</a></li><li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#lockfile">LockFile</a></li><li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxclients">MaxClients</a></li><li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxmemfree">MaxMemFree</a></li><li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxrequestsperchild">MaxRequestsPerChild</a></li><li><img alt="" src="../images/down.gif" /> <a href="#maxspareservers">MaxSpareServers</a></li><li><img alt="" src="../images/down.gif" /> <a href="#minspareservers">MinSpareServers</a></li><li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#pidfile">PidFile</a></li><li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#scoreboardfile">ScoreBoardFile</a></li><li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#sendbuffersize">SendBufferSize</a></li><li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#serverlimit">ServerLimit</a></li><li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#startservers">StartServers</a></li><li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#user">User</a></li></ul><h3>Topics</h3><ul id="topics"><li><img alt="" src="../images/down.gif" /> How it Works</li></ul><h3>See also</h3><ul class="seealso"><li><a href="../bind.html">Setting which addresses and
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ports Apache uses</a></li></ul></div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div><div class="section"><h2>How it Works</h2>
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<p>A single control process is responsible for launching child
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processes which listen for connections and serve them when they
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arrive. Apache always tries to maintain several <em>spare</em>
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or idle server processes, which stand ready to serve incoming
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requests. In this way, clients do not need to wait for a new
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child processes to be forked before their requests can be
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served.</p>
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<p>The <code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code>,
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<code class="directive"><a href="#minspareservers">MinSpareServers</a></code>,
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<code class="directive"><a href="#maxspareservers">MaxSpareServers</a></code>, and
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<code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code> regulate how
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the parent process creates children to serve requests. In general,
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Apache is very self-regulating, so most sites do not need to
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adjust these directives from their default values. Sites which
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need to serve more than 256 simultaneous requests may need to
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increase <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code>,
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while sites with limited memory may need to decrease <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code> to keep the server from
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thrashing (swapping memory to disk and back). More information
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about tuning process creation is provided in the <a href="../misc/perf-tuning.html">performance hints</a>
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documentation.</p>
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<p>While the parent process is usually started as root under Unix
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in order to bind to port 80, the child processes are launched by
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Apache as a less-privileged user. The <code class="directive"><a href="../mod/mpm_common.html#user">User</a></code> and <code class="directive"><a href="../mod/mpm_common.html#group">Group</a></code> directives are used to set
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the privileges of the Apache child processes. The child processes
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must be able to read all the content that will be served, but
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should have as few privileges beyond that as possible.</p>
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<p><code class="directive"><a href="../mod/mpm_common.html#maxrequestsperchild">MaxRequestsPerChild</a></code>
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controls how frequently the server recycles processes by killing
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old ones and launching new ones.</p>
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</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div><div class="directive-section"><h2><a name="AcceptMutex" id="AcceptMutex">AcceptMutex</a> <a name="acceptmutex" id="acceptmutex">Directive</a></h2><table class="directive"><tr><th><a href="directive-dict.html#Description">Description:
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</a></th><td>Method that Apache uses to serialize multiple children
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accepting requests on network sockets</td></tr><tr><th><a href="directive-dict.html#Syntax">Syntax:
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</a></th><td>AcceptMutex default|<em>method</em></td></tr><tr><th><a href="directive-dict.html#Default">Default:
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</a></th><td><code>AcceptMutex default</code></td></tr><tr><th><a href="directive-dict.html#Context">Context:
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</a></th><td>server config</td></tr><tr><th><a href="directive-dict.html#Status">Status:
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</a></th><td>MPM</td></tr><tr><th><a href="directive-dict.html#Module">Module:
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</a></th><td>prefork</td></tr></table>
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<p>The <code class="directive">AcceptMutex</code> directives sets the
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method that Apache uses to serialize multiple children accepting
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requests on network sockets. Prior to Apache 2.0, the method was
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selectable only at compile time. The optimal method to use is
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highly architecture and platform dependent. For further details,
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see the <a href="../misc/perf-tuning.html">performance tuning</a>
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documentation.</p>
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<p>If this directive is set to <code>default</code>, then the
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compile-time selected default will be used. Other possible
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methods are listed below. Note that not all methods are
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available on all platforms. If a method is specified which is
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not available, a message will be written to the error log
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listing the available methods.</p>
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<dl>
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<dt><code>flock</code></dt>
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<dd>uses the <code>flock(2)</code> system call to lock the
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file defined by the <code class="directive"><a href="../mod/mpm_common.html#lockfile">LockFile</a></code> directive.</dd>
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<dt><code>fcntl</code></dt>
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<dd>uses the <code>fnctl(2)</code> system call to lock the
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file defined by the <code class="directive"><a href="../mod/mpm_common.html#lockfile">LockFile</a></code> directive.</dd>
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<dt><code>sysvsem</code></dt>
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<dd>uses SySV-style semaphores to implement the mutex.</dd>
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<dt><code>pthread</code></dt>
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<dd>uses POSIX mutexes as implemented by the POSIX Threads
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(PThreads) specification.</dd>
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</dl>
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</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div><div class="directive-section"><h2><a name="MaxSpareServers" id="MaxSpareServers">MaxSpareServers</a> <a name="maxspareservers" id="maxspareservers">Directive</a></h2><table class="directive"><tr><th><a href="directive-dict.html#Description">Description:
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</a></th><td>Maximum number of idle child server processes</td></tr><tr><th><a href="directive-dict.html#Syntax">Syntax:
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</a></th><td>MaxSpareServers <em>number</em><br /></td></tr><tr><th><a href="directive-dict.html#Default">Default:
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</a></th><td><code>MaxSpareServers 10</code></td></tr><tr><th><a href="directive-dict.html#Context">Context:
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</a></th><td>server config</td></tr><tr><th><a href="directive-dict.html#Status">Status:
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</a></th><td>MPM</td></tr><tr><th><a href="directive-dict.html#Module">Module:
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</a></th><td>prefork</td></tr></table>
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<p>The <code class="directive">MaxSpareServers</code> directive sets the
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desired maximum number of <em>idle</em> child server processes. An
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idle process is one which is not handling a request. If there are
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more than MaxSpareServers idle, then the parent process will kill
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off the excess processes.</p>
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<p>Tuning of this parameter should only be necessary on very
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busy sites. Setting this parameter to a large number is almost
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always a bad idea.</p>
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<h3>See also</h3><ul><li><code class="directive"><a href="#minspareservers">MinSpareServers</a></code></li><li><code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code></li></ul></div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div><div class="directive-section"><h2><a name="MinSpareServers" id="MinSpareServers">MinSpareServers</a> <a name="minspareservers" id="minspareservers">Directive</a></h2><table class="directive"><tr><th><a href="directive-dict.html#Description">Description:
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</a></th><td>Minimum number of idle child server processes</td></tr><tr><th><a href="directive-dict.html#Syntax">Syntax:
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</a></th><td>MinSpareServers <em>number</em></td></tr><tr><th><a href="directive-dict.html#Default">Default:
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</a></th><td><code>MinSpareServers 5</code></td></tr><tr><th><a href="directive-dict.html#Context">Context:
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</a></th><td>server config</td></tr><tr><th><a href="directive-dict.html#Status">Status:
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</a></th><td>MPM</td></tr><tr><th><a href="directive-dict.html#Module">Module:
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</a></th><td>prefork</td></tr></table>
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<p>The <code class="directive">MinSpareServers</code> directive sets the
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desired minimum number of <em>idle</em> child server processes. An
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idle process is one which is not handling a request. If there are
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fewer than MinSpareServers idle, then the parent process creates
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new children at a maximum rate of 1 per second.</p>
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<p>Tuning of this parameter should only be necessary on very
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busy sites. Setting this parameter to a large number is almost
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always a bad idea.</p>
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<h3>See also</h3><ul><li><code class="directive"><a href="#maxspareservers">MaxSpareServers</a></code></li><li><code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code></li></ul></div></div><div id="footer"><p class="apache">Maintained by the <a href="http://httpd.apache.org/docs-project/">Apache HTTP Server Documentation Project</a></p><p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p></div></body></html> |