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16 <p class="apache">Apache HTTP Server Version 2.0</p>
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20 <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 2.0</a> > <a href="./">Modules</a></div>
21 <div id="page-content">
22 <div id="preamble"><h1>Apache MPM prefork</h1>
24 <p><span>Available Languages: </span><a href="../de/mod/prefork.html" hreflang="de" rel="alternate" title="Deutsch"> de </a> |
25 <a href="../en/mod/prefork.html" title="English"> en </a> |
26 <a href="../es/mod/prefork.html" hreflang="es" rel="alternate" title="Español"> es </a> |
27 <a href="../ja/mod/prefork.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
28 <a href="../tr/mod/prefork.html" hreflang="tr" rel="alternate" title="Türkçe"> tr </a></p>
30 <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>
31 <tr><th><a href="module-dict.html#Status">Status:</a></th><td>MPM</td></tr>
32 <tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>mpm_prefork_module</td></tr>
33 <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>prefork.c</td></tr></table>
36 <p>This Multi-Processing Module (MPM) implements a non-threaded,
37 pre-forking web server that handles requests in a manner similar
38 to Apache 1.3. It is appropriate for sites that need to avoid
39 threading for compatibility with non-thread-safe libraries. It
40 is also the best MPM for isolating each request, so that a problem
41 with a single request will not affect any other.</p>
43 <p>This MPM is very self-regulating, so it is rarely necessary to
44 adjust its configuration directives. Most important is that
45 <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code> be big enough to
46 handle as many simultaneous requests as you expect to receive, but
47 small enough to assure that there is enough physical RAM for all
50 <div id="quickview"><h3 class="directives">Directives</h3>
52 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#acceptmutex">AcceptMutex</a></li>
53 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#bs2000account">BS2000Account</a></li>
54 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#coredumpdirectory">CoreDumpDirectory</a></li>
55 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#enableexceptionhook">EnableExceptionHook</a></li>
56 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#group">Group</a></li>
57 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listen">Listen</a></li>
58 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listenbacklog">ListenBacklog</a></li>
59 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#lockfile">LockFile</a></li>
60 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxclients">MaxClients</a></li>
61 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxmemfree">MaxMemFree</a></li>
62 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxrequestsperchild">MaxRequestsPerChild</a></li>
63 <li><img alt="" src="../images/down.gif" /> <a href="#maxspareservers">MaxSpareServers</a></li>
64 <li><img alt="" src="../images/down.gif" /> <a href="#minspareservers">MinSpareServers</a></li>
65 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#pidfile">PidFile</a></li>
66 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#receivebuffersize">ReceiveBufferSize</a></li>
67 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#scoreboardfile">ScoreBoardFile</a></li>
68 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#sendbuffersize">SendBufferSize</a></li>
69 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#serverlimit">ServerLimit</a></li>
70 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#startservers">StartServers</a></li>
71 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#user">User</a></li>
75 <li><img alt="" src="../images/down.gif" /> <a href="#how-it-works">How it Works</a></li>
76 </ul><h3>See also</h3>
78 <li><a href="../bind.html">Setting which addresses and ports Apache
81 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
83 <h2><a name="how-it-works" id="how-it-works">How it Works</a></h2>
84 <p>A single control process is responsible for launching child
85 processes which listen for connections and serve them when they
86 arrive. Apache always tries to maintain several <dfn>spare</dfn>
87 or idle server processes, which stand ready to serve incoming
88 requests. In this way, clients do not need to wait for a new
89 child processes to be forked before their requests can be
92 <p>The <code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code>,
93 <code class="directive"><a href="#minspareservers">MinSpareServers</a></code>,
94 <code class="directive"><a href="#maxspareservers">MaxSpareServers</a></code>, and
95 <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code> regulate how
96 the parent process creates children to serve requests. In general,
97 Apache is very self-regulating, so most sites do not need to
98 adjust these directives from their default values. Sites which
99 need to serve more than 256 simultaneous requests may need to
100 increase <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code>,
101 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
102 thrashing (swapping memory to disk and back). More information
103 about tuning process creation is provided in the <a href="../misc/perf-tuning.html">performance hints</a>
106 <p>While the parent process is usually started as <code>root</code>
107 under Unix in order to bind to port 80, the child processes are
108 launched by 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
109 the privileges of the Apache child processes. The child processes
110 must be able to read all the content that will be served, but
111 should have as few privileges beyond that as possible.</p>
113 <p><code class="directive"><a href="../mod/mpm_common.html#maxrequestsperchild">MaxRequestsPerChild</a></code>
114 controls how frequently the server recycles processes by killing
115 old ones and launching new ones.</p>
117 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
118 <div class="directive-section"><h2><a name="MaxSpareServers" id="MaxSpareServers">MaxSpareServers</a> <a name="maxspareservers" id="maxspareservers">Directive</a></h2>
119 <table class="directive">
120 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Maximum number of idle child server processes</td></tr>
121 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MaxSpareServers <var>number</var></code></td></tr>
122 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MaxSpareServers 10</code></td></tr>
123 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
124 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
125 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>prefork</td></tr>
127 <p>The <code class="directive">MaxSpareServers</code> directive sets the
128 desired maximum number of <em>idle</em> child server processes. An
129 idle process is one which is not handling a request. If there are
130 more than <code class="directive">MaxSpareServers</code> idle, then the
131 parent process will kill off the excess processes.</p>
133 <p>Tuning of this parameter should only be necessary on very
134 busy sites. Setting this parameter to a large number is almost
135 always a bad idea. If you are trying to set the value lower than
136 <code class="directive"><a href="#minspareservers">MinSpareServers</a></code>, Apache
137 will automatically adjust it to <code class="directive">MinSpareServers</code><code> + 1</code>.</p>
141 <li><code class="directive"><a href="#minspareservers">MinSpareServers</a></code></li>
142 <li><code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code></li>
145 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
146 <div class="directive-section"><h2><a name="MinSpareServers" id="MinSpareServers">MinSpareServers</a> <a name="minspareservers" id="minspareservers">Directive</a></h2>
147 <table class="directive">
148 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Minimum number of idle child server processes</td></tr>
149 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MinSpareServers <var>number</var></code></td></tr>
150 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MinSpareServers 5</code></td></tr>
151 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
152 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
153 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>prefork</td></tr>
155 <p>The <code class="directive">MinSpareServers</code> directive sets the
156 desired minimum number of <em>idle</em> child server processes. An
157 idle process is one which is not handling a request. If there are
158 fewer than <code class="directive">MinSpareServers</code> idle, then the parent
159 process creates new children at a maximum rate of 1 per second.</p>
161 <p>Tuning of this parameter should only be necessary on very
162 busy sites. Setting this parameter to a large number is almost
163 always a bad idea.</p>
167 <li><code class="directive"><a href="#maxspareservers">MaxSpareServers</a></code></li>
168 <li><code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code></li>
172 <div class="bottomlang">
173 <p><span>Available Languages: </span><a href="../de/mod/prefork.html" hreflang="de" rel="alternate" title="Deutsch"> de </a> |
174 <a href="../en/mod/prefork.html" title="English"> en </a> |
175 <a href="../es/mod/prefork.html" hreflang="es" rel="alternate" title="Español"> es </a> |
176 <a href="../ja/mod/prefork.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
177 <a href="../tr/mod/prefork.html" hreflang="tr" rel="alternate" title="Türkçe"> tr </a></p>
178 </div><div id="footer">
179 <p class="apache">Copyright 2009 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
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