2 <!DOCTYPE modulesynopsis SYSTEM "../style/modulesynopsis.dtd">
3 <?xml-stylesheet type="text/xsl" href="../style/manual.en.xsl"?>
4 <modulesynopsis metafile="prefork.xml.meta">
7 <description>Implements a non-threaded, pre-forking web server</description>
9 <sourcefile>prefork.c</sourcefile>
10 <identifier>mpm_prefork_module</identifier>
13 <p>This Multi-Processing Module (MPM) implements a non-threaded,
14 pre-forking web server that handles requests in a manner similar
15 to Apache 1.3. It is appropriate for sites that need to avoid
16 threading for compatibility with non-thread-safe libraries. It
17 is also the best MPM for isolating each request, so that a problem
18 with a single request will not affect any other.</p>
20 <p>This MPM is very self-regulating, so it is rarely necessary to
21 adjust its configuration directives. Most important is that
22 <directive module="mpm_common">MaxClients</directive> be big enough to
23 handle as many simultaneous requests as you expect to receive, but
24 small enough to assure that there is enough physical RAM for all
27 <seealso><a href="../bind.html">Setting which addresses and ports Apache
30 <section id="how-it-works"><title>How it Works</title>
31 <p>A single control process is responsible for launching child
32 processes which listen for connections and serve them when they
33 arrive. Apache always tries to maintain several <dfn>spare</dfn>
34 or idle server processes, which stand ready to serve incoming
35 requests. In this way, clients do not need to wait for a new
36 child processes to be forked before their requests can be
39 <p>The <directive module="mpm_common">StartServers</directive>,
40 <directive module="prefork">MinSpareServers</directive>,
41 <directive module="prefork">MaxSpareServers</directive>, and
42 <directive module="mpm_common">MaxClients</directive> regulate how
43 the parent process creates children to serve requests. In general,
44 Apache is very self-regulating, so most sites do not need to
45 adjust these directives from their default values. Sites which
46 need to serve more than 256 simultaneous requests may need to
47 increase <directive module="mpm_common">MaxClients</directive>,
48 while sites with limited memory may need to decrease <directive
49 module="mpm_common">MaxClients</directive> to keep the server from
50 thrashing (swapping memory to disk and back). More information
51 about tuning process creation is provided in the <a
52 href="../misc/perf-tuning.html">performance hints</a>
55 <p>While the parent process is usually started as <code>root</code>
56 under Unix in order to bind to port 80, the child processes are
57 launched by Apache as a less-privileged user. The <directive
58 module="mpm_common">User</directive> and <directive
59 module="mpm_common">Group</directive> directives are used to set
60 the privileges of the Apache child processes. The child processes
61 must be able to read all the content that will be served, but
62 should have as few privileges beyond that as possible.</p>
64 <p><directive module="mpm_common">MaxRequestsPerChild</directive>
65 controls how frequently the server recycles processes by killing
66 old ones and launching new ones.</p>
69 <directivesynopsis location="mpm_common"><name>BS2000Account</name>
71 <directivesynopsis location="mpm_common"><name>CoreDumpDirectory</name>
73 <directivesynopsis location="mpm_common"><name>PidFile</name>
75 <directivesynopsis location="mpm_common"><name>Listen</name>
77 <directivesynopsis location="mpm_common"><name>ListenBacklog</name>
79 <directivesynopsis location="mpm_common"><name>LockFile</name>
81 <directivesynopsis location="mpm_common"><name>MaxClients</name>
83 <directivesynopsis location="mpm_common"><name>MaxMemFree</name>
85 <directivesynopsis location="mpm_common"><name>MaxRequestsPerChild</name>
87 <directivesynopsis location="mpm_common"><name>ScoreBoardFile</name>
89 <directivesynopsis location="mpm_common"><name>SendBufferSize</name>
91 <directivesynopsis location="mpm_common"><name>ServerLimit</name>
93 <directivesynopsis location="mpm_common"><name>StartServers</name>
95 <directivesynopsis location="mpm_common"><name>User</name>
97 <directivesynopsis location="mpm_common"><name>Group</name>
99 <directivesynopsis location="mpm_common"><name>AcceptMutex</name>
103 <name>MaxSpareServers</name>
104 <description>Maximum number of idle child server processes</description>
105 <syntax>MaxSpareServers <var>number</var><br /></syntax>
106 <default>MaxSpareServers 10</default>
107 <contextlist><context>server config</context></contextlist>
110 <p>The <directive>MaxSpareServers</directive> directive sets the
111 desired maximum number of <em>idle</em> child server processes. An
112 idle process is one which is not handling a request. If there are
113 more than <directive>MaxSpareServers</directive> idle, then the
114 parent process will kill off the excess processes.</p>
116 <p>Tuning of this parameter should only be necessary on very
117 busy sites. Setting this parameter to a large number is almost
118 always a bad idea. If you are trying to set the value lower than
119 <directive module="prefork">MinSpareServers</directive>, Apache
120 will automatically adjust it to <directive
121 >MinSpareServers</directive><code> + 1</code>.</p>
123 <seealso><directive module="prefork">MinSpareServers</directive></seealso>
124 <seealso><directive module="mpm_common">StartServers</directive></seealso>
128 <name>MinSpareServers</name>
129 <description>Minimum number of idle child server processes</description>
130 <syntax>MinSpareServers <var>number</var></syntax>
131 <default>MinSpareServers 5</default>
132 <contextlist><context>server config</context></contextlist>
135 <p>The <directive>MinSpareServers</directive> directive sets the
136 desired minimum number of <em>idle</em> child server processes. An
137 idle process is one which is not handling a request. If there are
138 fewer than <directive>MinSpareServers</directive> idle, then the parent
139 process creates new children at a maximum rate of 1 per second.</p>
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.</p>
145 <seealso><directive module="prefork">MaxSpareServers</directive></seealso>
146 <seealso><directive module="mpm_common">StartServers</directive></seealso>