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  10 <title>prefork - Apache HTTP Server Version 2.5</title>
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  20 <p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/quickreference.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>
  21 <p class="apache">Apache HTTP Server Version 2.5</p>
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  25 <a href="http://www.apache.org/">Apache</a> &gt; <a href="http://httpd.apache.org/">HTTP Server</a> &gt; <a href="http://httpd.apache.org/docs/">Documentation</a> &gt; <a href="../">Version 2.5</a> &gt; <a href="./">Modules</a></div>
  26 <div id="page-content">
  27 <div id="preamble"><h1>Apache MPM prefork</h1>
  28 <div class="toplang">
  29 <p><span>Available Languages: </span><a href="../de/mod/prefork.html" hreflang="de" rel="alternate" title="Deutsch">&nbsp;de&nbsp;</a> |
  30 <a href="../en/mod/prefork.html" title="English">&nbsp;en&nbsp;</a> |
  31 <a href="../ja/mod/prefork.html" hreflang="ja" rel="alternate" title="Japanese">&nbsp;ja&nbsp;</a> |
  32 <a href="../tr/mod/prefork.html" hreflang="tr" rel="alternate" title="Türkçe">&nbsp;tr&nbsp;</a></p>
  33 </div>
  34 <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>
  35 <tr><th><a href="module-dict.html#Status">Status:</a></th><td>MPM</td></tr>
  36 <tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>mpm_prefork_module</td></tr>
  37 <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>prefork.c</td></tr></table>
  38 <h3>Summary</h3>
  39
  40     <p>This Multi-Processing Module (MPM) implements a non-threaded,
  41     pre-forking web server. Each server process may answer incoming
  42     requests, and a parent process manages the size of the server pool.
  43     It is appropriate for sites that need to avoid
  44     threading for compatibility with non-thread-safe libraries.  It
  45     is also the best MPM for isolating each request, so that a problem
  46     with a single request will not affect any other.</p>
  47
  48     <p>This MPM is very self-regulating, so it is rarely necessary to
  49     adjust its configuration directives.  Most important is that
  50     <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code> be big enough
  51     to handle as many simultaneous requests as you expect to receive, but
  52     small enough to assure that there is enough physical RAM for all
  53     processes.</p>
  54 </div>
  55 <div id="quickview"><h3>Topics</h3>
  56 <ul id="topics">
  57 <li><img alt="" src="../images/down.gif" /> <a href="#how-it-works">How it Works</a></li>
  58 </ul><h3 class="directives">Directives</h3>
  59 <ul id="toc">
  60 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#coredumpdirectory">CoreDumpDirectory</a></li>
  61 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#enableexceptionhook">EnableExceptionHook</a></li>
  62 <li><img alt="" src="../images/right.gif" /> <a href="mod_unixd.html#group">Group</a></li>
  63 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listen">Listen</a></li>
  64 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listenbacklog">ListenBacklog</a></li>
  65 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxconnectionsperchild">MaxConnectionsPerChild</a></li>
  66 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxmemfree">MaxMemFree</a></li>
  67 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></li>
  68 <li><img alt="" src="../images/down.gif" /> <a href="#maxspareservers">MaxSpareServers</a></li>
  69 <li><img alt="" src="../images/down.gif" /> <a href="#minspareservers">MinSpareServers</a></li>
  70 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#pidfile">PidFile</a></li>
  71 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#receivebuffersize">ReceiveBufferSize</a></li>
  72 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#scoreboardfile">ScoreBoardFile</a></li>
  73 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#sendbuffersize">SendBufferSize</a></li>
  74 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#serverlimit">ServerLimit</a></li>
  75 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#startservers">StartServers</a></li>
  76 <li><img alt="" src="../images/right.gif" /> <a href="mod_unixd.html#user">User</a></li>
  77 </ul>
  78 <h3>Bugfix checklist</h3><ul class="seealso"><li><a href="https://www.apache.org/dist/httpd/CHANGES_2.4">httpd changelog</a></li><li><a href="https://bz.apache.org/bugzilla/buglist.cgi?bug_status=__open__&amp;list_id=144532&amp;product=Apache%20httpd-2&amp;query_format=specific&amp;order=changeddate%20DESC%2Cpriority%2Cbug_severity&amp;component=mpm_prefork">Known issues</a></li><li><a href="https://bz.apache.org/bugzilla/enter_bug.cgi?product=Apache%20httpd-2&amp;component=mpm_prefork">Report a bug</a></li></ul><h3>See also</h3>
  79 <ul class="seealso">
  80 <li><a href="../bind.html">Setting which addresses and ports Apache HTTP Server
  81 uses</a></li>
  82 </ul><ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div>
  83 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
  84 <div class="section">
  85 <h2><a name="how-it-works" id="how-it-works">How it Works</a></h2>
  86     <p>A single control process is responsible for launching child
  87     processes which listen for connections and serve them when they
  88     arrive. Apache httpd always tries to maintain several <dfn>spare</dfn>
  89     or idle server processes, which stand ready to serve incoming
  90     requests. In this way, clients do not need to wait for a new
  91     child processes to be forked before their requests can be
  92     served.</p>
  93
  94     <p>The <code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code>,
  95     <code class="directive"><a href="#minspareservers">MinSpareServers</a></code>,
  96     <code class="directive"><a href="#maxspareservers">MaxSpareServers</a></code>, and
  97     <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code> regulate how
  98     the parent process creates children to serve requests. In general,
  99     Apache httpd is very self-regulating, so most sites do not need to
 100     adjust these directives from their default values. Sites which
 101     need to serve more than 256 simultaneous requests may need to
 102     increase <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code>,
 103     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
 104     thrashing (swapping memory to disk and back). More information
 105     about tuning process creation is provided in the <a href="../misc/perf-tuning.html">performance hints</a>
 106     documentation.</p>
 107
 108     <p>While the parent process is usually started as <code>root</code>
 109     under Unix in order to bind to port 80, the child processes are
 110     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
 111     the privileges of the Apache httpd child processes. The child processes
 112     must be able to read all the content that will be served, but
 113     should have as few privileges beyond that as possible.</p>
 114
 115     <p><code class="directive"><a href="../mod/mpm_common.html#maxconnectionsperchild">MaxConnectionsPerChild</a></code>
 116     controls how frequently the server recycles processes by killing
 117     old ones and launching new ones.</p>
 118
 119     <p>This MPM uses the <code>mpm-accept</code> mutex to serialize
 120     access to incoming connections when subject to the thundering herd
 121     problem (generally, when there are multiple listening sockets).
 122     The implementation aspects of this mutex can be configured with the
 123     <code class="directive"><a href="../mod/core.html#mutex">Mutex</a></code> directive.  The <a href="../misc/perf-tuning.html">performance hints</a>
 124     documentation has additional information about this mutex.</p>
 125 </div>
 126 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 127 <div class="directive-section"><h2><a name="MaxSpareServers" id="MaxSpareServers">MaxSpareServers</a> <a name="maxspareservers" id="maxspareservers">Directive</a></h2>
 128 <table class="directive">
 129 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Maximum number of idle child server processes</td></tr>
 130 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MaxSpareServers <var>number</var></code></td></tr>
 131 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MaxSpareServers 10</code></td></tr>
 132 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
 133 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
 134 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>prefork</td></tr>
 135 </table>
 136     <p>The <code class="directive">MaxSpareServers</code> directive sets the
 137     desired maximum number of <em>idle</em> child server processes. An
 138     idle process is one which is not handling a request. If there are
 139     more than <code class="directive">MaxSpareServers</code> idle, then the
 140     parent process will kill off the excess processes.</p>
 141
 142     <p>Tuning of this parameter should only be necessary on very
 143     busy sites. Setting this parameter to a large number is almost
 144     always a bad idea. If you are trying to set the value equal to or lower than
 145     <code class="directive"><a href="#minspareservers">MinSpareServers</a></code>, Apache HTTP Server
 146     will automatically adjust it to <code class="directive">MinSpareServers</code><code> + 1</code>.</p>
 147
 148 <h3>See also</h3>
 149 <ul>
 150 <li><code class="directive"><a href="#minspareservers">MinSpareServers</a></code></li>
 151 <li><code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code></li>
 152 <li><code class="directive"><a href="../mod/mpm_common.html#maxsparethreads">MaxSpareThreads</a></code></li>
 153 </ul>
 154 </div>
 155 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 156 <div class="directive-section"><h2><a name="MinSpareServers" id="MinSpareServers">MinSpareServers</a> <a name="minspareservers" id="minspareservers">Directive</a></h2>
 157 <table class="directive">
 158 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Minimum number of idle child server processes</td></tr>
 159 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MinSpareServers <var>number</var></code></td></tr>
 160 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MinSpareServers 5</code></td></tr>
 161 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
 162 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
 163 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>prefork</td></tr>
 164 </table>
 165     <p>The <code class="directive">MinSpareServers</code> directive sets the
 166     desired minimum number of <em>idle</em> child server processes. An
 167     idle process is one which is not handling a request. If there are
 168     fewer than <code class="directive">MinSpareServers</code> idle, then the parent
 169     process creates new children: It will spawn one, wait a second, then spawn
 170     two, wait a second, then spawn four, and it will
 171     continue exponentially until it is spawning 32 children per second. It will
 172     stop whenever it satisfies the <code class="directive">MinSpareServers</code>
 173     setting.</p>
 174
 175     <p>Tuning of this parameter should only be necessary on very
 176     busy sites. Setting this parameter to a large number is almost
 177     always a bad idea.</p>
 178
 179 <h3>See also</h3>
 180 <ul>
 181 <li><code class="directive"><a href="#maxspareservers">MaxSpareServers</a></code></li>
 182 <li><code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code></li>
 183 <li><code class="directive"><a href="../mod/mpm_common.html#minsparethreads">MinSpareThreads</a></code></li>
 184 </ul>
 185 </div>
 186 </div>
 187 <div class="bottomlang">
 188 <p><span>Available Languages: </span><a href="../de/mod/prefork.html" hreflang="de" rel="alternate" title="Deutsch">&nbsp;de&nbsp;</a> |
 189 <a href="../en/mod/prefork.html" title="English">&nbsp;en&nbsp;</a> |
 190 <a href="../ja/mod/prefork.html" hreflang="ja" rel="alternate" title="Japanese">&nbsp;ja&nbsp;</a> |
 191 <a href="../tr/mod/prefork.html" hreflang="tr" rel="alternate" title="Türkçe">&nbsp;tr&nbsp;</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&amp;A section. Comments placed here should be pointed towards suggestions on improving the documentation or server, and may be removed again by our moderators if they are either implemented or considered invalid/off-topic. Questions on how to manage the Apache HTTP Server should be directed at either our IRC channel, #httpd, on Freenode, or sent to our <a href="http://httpd.apache.org/lists.html">mailing lists</a>.</div>
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