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