1<?xml version="1.0" encoding="ISO-8859-1"?> 2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> 3<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head><!-- 4 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX 5 This file is generated from xml source: DO NOT EDIT 6 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX 7 --> 8<title>prefork - Apache HTTP Server</title> 9<link href="/style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" /> 10<link href="/style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" /> 11<link href="/style/css/manual-print.css" rel="stylesheet" media="print" type="text/css" /><link rel="stylesheet" type="text/css" href="/style/css/prettify.css" /> 12<script src="/style/scripts/prettify.min.js" type="text/javascript"> 13</script> 14 15<link href="/images/favicon.ico" rel="shortcut icon" /></head> 16<body> 17<div id="page-header"> 18<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> 19<p class="apache">Apache HTTP Server Version 2.4</p> 20<img alt="" src="/images/feather.gif" /></div> 21<div class="up"><a href="./"><img title="<-" alt="<-" src="/images/left.gif" /></a></div> 22<div id="path"> 23<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 2.4</a> > <a href="./">Modules</a></div> 24<div id="page-content"> 25<div id="preamble"><h1>Apache MPM prefork</h1> 26<div class="toplang"> 27<p><span>Available Languages: </span><a href="/de/mod/prefork.html" hreflang="de" rel="alternate" title="Deutsch"> de </a> | 28<a href="/en/mod/prefork.html" title="English"> en </a> | 29<a href="/fr/mod/prefork.html" hreflang="fr" rel="alternate" title="Fran�ais"> fr </a> | 30<a href="/ja/mod/prefork.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> | 31<a href="/tr/mod/prefork.html" hreflang="tr" rel="alternate" title="T�rk�e"> tr </a></p> 32</div> 33<table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Implements a non-threaded, pre-forking web server</td></tr> 34<tr><th><a href="module-dict.html#Status">Status:</a></th><td>MPM</td></tr> 35<tr><th><a href="module-dict.html#ModuleIdentifier">Module�Identifier:</a></th><td>mpm_prefork_module</td></tr> 36<tr><th><a href="module-dict.html#SourceFile">Source�File:</a></th><td>prefork.c</td></tr></table> 37<h3>Summary</h3> 38 39 <p>This Multi-Processing Module (MPM) implements a non-threaded, 40 pre-forking web server. Each server process may answer incoming 41 requests, and a parent process manages the size of the server pool. 42 It is appropriate for sites that need to avoid 43 threading for compatibility with non-thread-safe libraries. It 44 is also the best MPM for isolating each request, so that a problem 45 with a single request will not affect any other.</p> 46 47 <p>This MPM is very self-regulating, so it is rarely necessary to 48 adjust its configuration directives. Most important is that 49 <code class="directive"><a href="/mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code> be big enough 50 to handle as many simultaneous requests as you expect to receive, but 51 small enough to assure that there is enough physical RAM for all 52 processes.</p> 53</div> 54<div id="quickview"><h3 class="directives">Directives</h3> 55<ul id="toc"> 56<li><img alt="" src="/images/right.gif" /> <a href="mpm_common.html#coredumpdirectory">CoreDumpDirectory</a></li> 57<li><img alt="" src="/images/right.gif" /> <a href="mpm_common.html#enableexceptionhook">EnableExceptionHook</a></li> 58<li><img alt="" src="/images/right.gif" /> <a href="mod_unixd.html#group">Group</a></li> 59<li><img alt="" src="/images/right.gif" /> <a href="mpm_common.html#listen">Listen</a></li> 60<li><img alt="" src="/images/right.gif" /> <a href="mpm_common.html#listenbacklog">ListenBacklog</a></li> 61<li><img alt="" src="/images/right.gif" /> <a href="mpm_common.html#maxconnectionsperchild">MaxConnectionsPerChild</a></li> 62<li><img alt="" src="/images/right.gif" /> <a href="mpm_common.html#maxmemfree">MaxMemFree</a></li> 63<li><img alt="" src="/images/right.gif" /> <a href="mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></li> 64<li><img alt="" src="/images/down.gif" /> <a href="#maxspareservers">MaxSpareServers</a></li> 65<li><img alt="" src="/images/down.gif" /> <a href="#minspareservers">MinSpareServers</a></li> 66<li><img alt="" src="/images/right.gif" /> <a href="mpm_common.html#pidfile">PidFile</a></li> 67<li><img alt="" src="/images/right.gif" /> <a href="mpm_common.html#receivebuffersize">ReceiveBufferSize</a></li> 68<li><img alt="" src="/images/right.gif" /> <a href="mpm_common.html#scoreboardfile">ScoreBoardFile</a></li> 69<li><img alt="" src="/images/right.gif" /> <a href="mpm_common.html#sendbuffersize">SendBufferSize</a></li> 70<li><img alt="" src="/images/right.gif" /> <a href="mpm_common.html#serverlimit">ServerLimit</a></li> 71<li><img alt="" src="/images/right.gif" /> <a href="mpm_common.html#startservers">StartServers</a></li> 72<li><img alt="" src="/images/right.gif" /> <a href="mod_unixd.html#user">User</a></li> 73</ul> 74<h3>Topics</h3> 75<ul id="topics"> 76<li><img alt="" src="/images/down.gif" /> <a href="#how-it-works">How it Works</a></li> 77</ul><h3>See also</h3> 78<ul class="seealso"> 79<li><a href="/bind.html">Setting which addresses and ports Apache HTTP Server 80uses</a></li> 81</ul><ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div> 82<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div> 83<div class="section"> 84<h2><a name="how-it-works" id="how-it-works">How it Works</a></h2> 85 <p>A single control process is responsible for launching child 86 processes which listen for connections and serve them when they 87 arrive. Apache httpd always tries to maintain several <dfn>spare</dfn> 88 or idle server processes, which stand ready to serve incoming 89 requests. In this way, clients do not need to wait for a new 90 child processes to be forked before their requests can be 91 served.</p> 92 93 <p>The <code class="directive"><a href="/mod/mpm_common.html#startservers">StartServers</a></code>, 94 <code class="directive"><a href="#minspareservers">MinSpareServers</a></code>, 95 <code class="directive"><a href="#maxspareservers">MaxSpareServers</a></code>, and 96 <code class="directive"><a href="/mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code> regulate how 97 the parent process creates children to serve requests. In general, 98 Apache httpd is very self-regulating, so most sites do not need to 99 adjust these directives from their default values. Sites which 100 need to serve more than 256 simultaneous requests may need to 101 increase <code class="directive"><a href="/mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code>, 102 while sites with limited memory may need to decrease <code class="directive"><a href="/mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code> to keep the server from 103 thrashing (swapping memory to disk and back). More information 104 about tuning process creation is provided in the <a href="/misc/perf-tuning.html">performance hints</a> 105 documentation.</p> 106 107 <p>While the parent process is usually started as <code>root</code> 108 under Unix in order to bind to port 80, the child processes are 109 launched by Apache httpd as a less-privileged user. The <code class="directive"><a href="/mod/mod_unixd.html#user">User</a></code> and <code class="directive"><a href="/mod/mod_unixd.html#group">Group</a></code> directives are used to set 110 the privileges of the Apache httpd child processes. The child processes 111 must be able to read all the content that will be served, but 112 should have as few privileges beyond that as possible.</p> 113 114 <p><code class="directive"><a href="/mod/mpm_common.html#maxconnectionsperchild">MaxConnectionsPerChild</a></code> 115 controls how frequently the server recycles processes by killing 116 old ones and launching new ones.</p> 117 118 <p>This MPM uses the <code>mpm-accept</code> mutex to serialize 119 access to incoming connections when subject to the thundering herd 120 problem (generally, when there are multiple listening sockets). 121 The implementation aspects of this mutex can be configured with the 122 <code class="directive"><a href="/mod/core.html#mutex">Mutex</a></code> directive. The <a href="/misc/perf-tuning.html">performance hints</a> 123 documentation has additional information about this mutex.</p> 124</div> 125<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div> 126<div class="directive-section"><h2><a name="MaxSpareServers" id="MaxSpareServers">MaxSpareServers</a> <a name="maxspareservers" id="maxspareservers">Directive</a></h2> 127<table class="directive"> 128<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Maximum number of idle child server processes</td></tr> 129<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MaxSpareServers <var>number</var></code></td></tr> 130<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MaxSpareServers 10</code></td></tr> 131<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr> 132<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr> 133<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>prefork</td></tr> 134</table> 135 <p>The <code class="directive">MaxSpareServers</code> directive sets the 136 desired maximum number of <em>idle</em> child server processes. An 137 idle process is one which is not handling a request. If there are 138 more than <code class="directive">MaxSpareServers</code> idle, then the 139 parent process will kill off the excess processes.</p> 140 141 <p>Tuning of this parameter should only be necessary on very 142 busy sites. Setting this parameter to a large number is almost 143 always a bad idea. If you are trying to set the value equal to or lower than 144 <code class="directive"><a href="#minspareservers">MinSpareServers</a></code>, Apache HTTP Server 145 will automatically adjust it to <code class="directive">MinSpareServers</code><code> + 1</code>.</p> 146 147<h3>See also</h3> 148<ul> 149<li><code class="directive"><a href="#minspareservers">MinSpareServers</a></code></li> 150<li><code class="directive"><a href="/mod/mpm_common.html#startservers">StartServers</a></code></li> 151<li><code class="directive"><a href="/mod/mpm_common.html#maxsparethreads">MaxSpareThreads</a></code></li> 152</ul> 153</div> 154<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div> 155<div class="directive-section"><h2><a name="MinSpareServers" id="MinSpareServers">MinSpareServers</a> <a name="minspareservers" id="minspareservers">Directive</a></h2> 156<table class="directive"> 157<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Minimum number of idle child server processes</td></tr> 158<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MinSpareServers <var>number</var></code></td></tr> 159<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MinSpareServers 5</code></td></tr> 160<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr> 161<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr> 162<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>prefork</td></tr> 163</table> 164 <p>The <code class="directive">MinSpareServers</code> directive sets the 165 desired minimum number of <em>idle</em> child server processes. An 166 idle process is one which is not handling a request. If there are 167 fewer than <code class="directive">MinSpareServers</code> idle, then the parent 168 process creates new children: It will spawn one, wait a second, then spawn 169 two, wait a second, then spawn four, and it will 170 continue exponentially until it is spawning 32 children per second. It will 171 stop whenever it satisfies the <code class="directive">MinSpareServers</code> 172 setting.</p> 173 174 <p>Tuning of this parameter should only be necessary on very 175 busy sites. Setting this parameter to a large number is almost 176 always a bad idea.</p> 177 178<h3>See also</h3> 179<ul> 180<li><code class="directive"><a href="#maxspareservers">MaxSpareServers</a></code></li> 181<li><code class="directive"><a href="/mod/mpm_common.html#startservers">StartServers</a></code></li> 182<li><code class="directive"><a href="/mod/mpm_common.html#minsparethreads">MinSpareThreads</a></code></li> 183</ul> 184</div> 185</div> 186<div class="bottomlang"> 187<p><span>Available Languages: </span><a href="/de/mod/prefork.html" hreflang="de" rel="alternate" title="Deutsch"> de </a> | 188<a href="/en/mod/prefork.html" title="English"> en </a> | 189<a href="/fr/mod/prefork.html" hreflang="fr" rel="alternate" title="Fran�ais"> fr </a> | 190<a href="/ja/mod/prefork.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> | 191<a href="/tr/mod/prefork.html" hreflang="tr" rel="alternate" title="T�rk�e"> tr </a></p> 192</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. 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