2 <!DOCTYPE modulesynopsis SYSTEM "../style/modulesynopsis.dtd">
3 <?xml-stylesheet type="text/xsl" href="../style/manual.en.xsl"?>
4 <!-- $LastChangedRevision$ -->
7 Copyright 2002-2004 The Apache Software Foundation
9 Licensed under the Apache License, Version 2.0 (the "License");
10 you may not use this file except in compliance with the License.
11 You may obtain a copy of the License at
13 http://www.apache.org/licenses/LICENSE-2.0
15 Unless required by applicable law or agreed to in writing, software
16 distributed under the License is distributed on an "AS IS" BASIS,
17 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
18 See the License for the specific language governing permissions and
19 limitations under the License.
22 <modulesynopsis metafile="prefork.xml.meta">
25 <description>Implements a non-threaded, pre-forking web server</description>
27 <sourcefile>prefork.c</sourcefile>
28 <identifier>mpm_prefork_module</identifier>
31 <p>This Multi-Processing Module (MPM) implements a non-threaded,
32 pre-forking web server that handles requests in a manner similar
33 to Apache 1.3. It is appropriate for sites that need to avoid
34 threading for compatibility with non-thread-safe libraries. It
35 is also the best MPM for isolating each request, so that a problem
36 with a single request will not affect any other.</p>
38 <p>This MPM is very self-regulating, so it is rarely necessary to
39 adjust its configuration directives. Most important is that
40 <directive module="mpm_common">MaxClients</directive> be big enough to
41 handle as many simultaneous requests as you expect to receive, but
42 small enough to assure that there is enough physical RAM for all
45 <seealso><a href="../bind.html">Setting which addresses and ports Apache
48 <section id="how-it-works"><title>How it Works</title>
49 <p>A single control process is responsible for launching child
50 processes which listen for connections and serve them when they
51 arrive. Apache always tries to maintain several <dfn>spare</dfn>
52 or idle server processes, which stand ready to serve incoming
53 requests. In this way, clients do not need to wait for a new
54 child processes to be forked before their requests can be
57 <p>The <directive module="mpm_common">StartServers</directive>,
58 <directive module="prefork">MinSpareServers</directive>,
59 <directive module="prefork">MaxSpareServers</directive>, and
60 <directive module="mpm_common">MaxClients</directive> regulate how
61 the parent process creates children to serve requests. In general,
62 Apache is very self-regulating, so most sites do not need to
63 adjust these directives from their default values. Sites which
64 need to serve more than 256 simultaneous requests may need to
65 increase <directive module="mpm_common">MaxClients</directive>,
66 while sites with limited memory may need to decrease <directive
67 module="mpm_common">MaxClients</directive> to keep the server from
68 thrashing (swapping memory to disk and back). More information
69 about tuning process creation is provided in the <a
70 href="../misc/perf-tuning.html">performance hints</a>
73 <p>While the parent process is usually started as <code>root</code>
74 under Unix in order to bind to port 80, the child processes are
75 launched by Apache as a less-privileged user. The <directive
76 module="mpm_common">User</directive> and <directive
77 module="mpm_common">Group</directive> directives are used to set
78 the privileges of the Apache child processes. The child processes
79 must be able to read all the content that will be served, but
80 should have as few privileges beyond that as possible.</p>
82 <p><directive module="mpm_common">MaxRequestsPerChild</directive>
83 controls how frequently the server recycles processes by killing
84 old ones and launching new ones.</p>
87 <directivesynopsis location="mpm_common"><name>CoreDumpDirectory</name>
89 <directivesynopsis location="mpm_common"><name>EnableExceptionHook</name>
91 <directivesynopsis location="mpm_common"><name>PidFile</name>
93 <directivesynopsis location="mpm_common"><name>Listen</name>
95 <directivesynopsis location="mpm_common"><name>ListenBacklog</name>
97 <directivesynopsis location="mpm_common"><name>LockFile</name>
99 <directivesynopsis location="mpm_common"><name>MaxClients</name>
101 <directivesynopsis location="mpm_common"><name>MaxMemFree</name>
103 <directivesynopsis location="mpm_common"><name>MaxRequestsPerChild</name>
105 <directivesynopsis location="mpm_common"><name>ScoreBoardFile</name>
107 <directivesynopsis location="mpm_common"><name>SendBufferSize</name>
109 <directivesynopsis location="mpm_common"><name>ServerLimit</name>
111 <directivesynopsis location="mpm_common"><name>StartServers</name>
113 <directivesynopsis location="mpm_common"><name>User</name>
115 <directivesynopsis location="mpm_common"><name>Group</name>
117 <directivesynopsis location="mpm_common"><name>AcceptMutex</name>
121 <name>MaxSpareServers</name>
122 <description>Maximum number of idle child server processes</description>
123 <syntax>MaxSpareServers <var>number</var></syntax>
124 <default>MaxSpareServers 10</default>
125 <contextlist><context>server config</context></contextlist>
128 <p>The <directive>MaxSpareServers</directive> directive sets the
129 desired maximum number of <em>idle</em> child server processes. An
130 idle process is one which is not handling a request. If there are
131 more than <directive>MaxSpareServers</directive> idle, then the
132 parent process will kill off the excess processes.</p>
134 <p>Tuning of this parameter should only be necessary on very
135 busy sites. Setting this parameter to a large number is almost
136 always a bad idea. If you are trying to set the value equal to or lower than
137 <directive module="prefork">MinSpareServers</directive>, Apache
138 will automatically adjust it to <directive
139 >MinSpareServers</directive><code> + 1</code>.</p>
141 <seealso><directive module="prefork">MinSpareServers</directive></seealso>
142 <seealso><directive module="mpm_common">StartServers</directive></seealso>
146 <name>MinSpareServers</name>
147 <description>Minimum number of idle child server processes</description>
148 <syntax>MinSpareServers <var>number</var></syntax>
149 <default>MinSpareServers 5</default>
150 <contextlist><context>server config</context></contextlist>
153 <p>The <directive>MinSpareServers</directive> directive sets the
154 desired minimum number of <em>idle</em> child server processes. An
155 idle process is one which is not handling a request. If there are
156 fewer than <directive>MinSpareServers</directive> idle, then the parent
157 process creates new children at a maximum rate of 1 per second.</p>
159 <p>Tuning of this parameter should only be necessary on very
160 busy sites. Setting this parameter to a large number is almost
161 always a bad idea.</p>
163 <seealso><directive module="prefork">MaxSpareServers</directive></seealso>
164 <seealso><directive module="mpm_common">StartServers</directive></seealso>