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  10 <title>mpm_common - 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>
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  26 <div id="page-content">
  27 <div id="preamble"><h1>Apache MPM Common Directives</h1>
  28 <div class="toplang">
  29 <p><span>Available Languages: </span><a href="../de/mod/mpm_common.html" hreflang="de" rel="alternate" title="Deutsch">&nbsp;de&nbsp;</a> |
  30 <a href="../en/mod/mpm_common.html" title="English">&nbsp;en&nbsp;</a> |
  31 <a href="../ja/mod/mpm_common.html" hreflang="ja" rel="alternate" title="Japanese">&nbsp;ja&nbsp;</a> |
  32 <a href="../tr/mod/mpm_common.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>A collection of directives that are implemented by
  35 more than one multi-processing module (MPM)</td></tr>
  36 <tr><th><a href="module-dict.html#Status">Status:</a></th><td>MPM</td></tr></table>
  37 </div>
  38 <div id="quickview"><h3 class="directives">Directives</h3>
  39 <ul id="toc">
  40 <li><img alt="" src="../images/down.gif" /> <a href="#coredumpdirectory">CoreDumpDirectory</a></li>
  41 <li><img alt="" src="../images/down.gif" /> <a href="#enableexceptionhook">EnableExceptionHook</a></li>
  42 <li><img alt="" src="../images/down.gif" /> <a href="#gracefulshutdowntimeout">GracefulShutdownTimeout</a></li>
  43 <li><img alt="" src="../images/down.gif" /> <a href="#listen">Listen</a></li>
  44 <li><img alt="" src="../images/down.gif" /> <a href="#listenbacklog">ListenBackLog</a></li>
  45 <li><img alt="" src="../images/down.gif" /> <a href="#listencoresbucketsratio">ListenCoresBucketsRatio</a></li>
  46 <li><img alt="" src="../images/down.gif" /> <a href="#maxconnectionsperchild">MaxConnectionsPerChild</a></li>
  47 <li><img alt="" src="../images/down.gif" /> <a href="#maxmemfree">MaxMemFree</a></li>
  48 <li><img alt="" src="../images/down.gif" /> <a href="#maxrequestworkers">MaxRequestWorkers</a></li>
  49 <li><img alt="" src="../images/down.gif" /> <a href="#maxsparethreads">MaxSpareThreads</a></li>
  50 <li><img alt="" src="../images/down.gif" /> <a href="#minsparethreads">MinSpareThreads</a></li>
  51 <li><img alt="" src="../images/down.gif" /> <a href="#pidfile">PidFile</a></li>
  52 <li><img alt="" src="../images/down.gif" /> <a href="#receivebuffersize">ReceiveBufferSize</a></li>
  53 <li><img alt="" src="../images/down.gif" /> <a href="#scoreboardfile">ScoreBoardFile</a></li>
  54 <li><img alt="" src="../images/down.gif" /> <a href="#sendbuffersize">SendBufferSize</a></li>
  55 <li><img alt="" src="../images/down.gif" /> <a href="#serverlimit">ServerLimit</a></li>
  56 <li><img alt="" src="../images/down.gif" /> <a href="#startservers">StartServers</a></li>
  57 <li><img alt="" src="../images/down.gif" /> <a href="#startthreads">StartThreads</a></li>
  58 <li><img alt="" src="../images/down.gif" /> <a href="#threadlimit">ThreadLimit</a></li>
  59 <li><img alt="" src="../images/down.gif" /> <a href="#threadsperchild">ThreadsPerChild</a></li>
  60 <li><img alt="" src="../images/down.gif" /> <a href="#threadstacksize">ThreadStackSize</a></li>
  61 </ul>
  62 <ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div>
  63
  64 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
  65 <div class="directive-section"><h2><a name="CoreDumpDirectory" id="CoreDumpDirectory">CoreDumpDirectory</a> <a name="coredumpdirectory" id="coredumpdirectory">Directive</a></h2>
  66 <table class="directive">
  67 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Directory where Apache HTTP Server attempts to
  68 switch before dumping core</td></tr>
  69 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CoreDumpDirectory <var>directory</var></code></td></tr>
  70 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>See usage for the default setting</code></td></tr>
  71 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
  72 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
  73 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="../mod/event.html">event</a></code>, <code class="module"><a href="../mod/worker.html">worker</a></code>, <code class="module"><a href="../mod/prefork.html">prefork</a></code></td></tr>
  74 </table>
  75     <p>This controls the directory to which Apache httpd attempts to
  76     switch before dumping core. If your operating system is configured to
  77     create core files in the working directory of the crashing process,
  78     <code class="directive">CoreDumpDirectory</code> is necessary to change working
  79     directory from the default <code class="directive"><a href="../mod/core.html#serverroot">ServerRoot</a></code>
  80     directory, which should not be writable by the user the server runs as.</p>
  81
  82     <p>If you want a core dump for debugging, you can use this directive to
  83     place it in a different location. This directive has no effect if your
  84     operating system is not configured to write core files to the working directory
  85     of the crashing processes.</p>
  86
  87     <div class="note"><h3>Core Dumps on Linux</h3>
  88       <p>If Apache httpd starts as root and switches to another user, the
  89       Linux kernel <em>disables</em> core dumps even if the directory is
  90       writable for the process. Apache httpd (2.0.46 and later) reenables core dumps
  91       on Linux 2.4 and beyond, but only if you explicitly configure a <code class="directive">CoreDumpDirectory</code>.</p>
  92     </div>
  93
  94     <div class="note">
  95     <h3>Core Dumps on BSD</h3>
  96     <p>To enable core-dumping of suid-executables on BSD-systems (such
  97     as FreeBSD), set <code>kern.sugid_coredump</code> to 1.
  98     </p>
  99     </div>
 100
 101     <div class="note"><h3>Specific signals</h3>
 102       <p><code class="directive">CoreDumpDirectory</code> processing only occurs for
 103       a select set of fatal signals: SIGFPE, SIGILL, SIGABORT,
 104       SIGSEGV, and SIGBUS.</p>
 105       <p>On some operating systems, SIGQUIT also results in a core dump but
 106       does not go through <code class="directive">CoreDumpDirectory</code> or
 107       <code class="directive">EnableExceptionHook</code> processing, so the core
 108       location is dictated entirely by the operating system.</p>
 109     </div>
 110
 111
 112 </div>
 113 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 114 <div class="directive-section"><h2><a name="EnableExceptionHook" id="EnableExceptionHook">EnableExceptionHook</a> <a name="enableexceptionhook" id="enableexceptionhook">Directive</a></h2>
 115 <table class="directive">
 116 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Enables a hook that runs exception handlers
 117 after a crash</td></tr>
 118 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>EnableExceptionHook On|Off</code></td></tr>
 119 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>EnableExceptionHook Off</code></td></tr>
 120 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
 121 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
 122 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="../mod/event.html">event</a></code>, <code class="module"><a href="../mod/worker.html">worker</a></code>, <code class="module"><a href="../mod/prefork.html">prefork</a></code></td></tr>
 123 </table>
 124     <p>For safety reasons this directive is only available if the server was
 125     configured with the <code>--enable-exception-hook</code> option. It
 126     enables a hook that allows external modules to plug in and do something
 127     after a child crashed.</p>
 128
 129     <p>There are already two modules, <code>mod_whatkilledus</code> and
 130     <code>mod_backtrace</code> that make use of this hook. Please have a
 131     look at Jeff Trawick's <a href="http://people.apache.org/~trawick/exception_hook.html">EnableExceptionHook site</a> for more information about these.</p>
 132
 133 </div>
 134 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 135 <div class="directive-section"><h2><a name="GracefulShutdownTimeout" id="GracefulShutdownTimeout">GracefulShutdownTimeout</a> <a name="gracefulshutdowntimeout" id="gracefulshutdowntimeout">Directive</a></h2>
 136 <table class="directive">
 137 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Specify a timeout after which a gracefully shutdown server
 138 will exit.</td></tr>
 139 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>GracefulShutdownTimeout <var>seconds</var></code></td></tr>
 140 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>GracefulShutdownTimeout 0</code></td></tr>
 141 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
 142 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
 143 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="../mod/event.html">event</a></code>, <code class="module"><a href="../mod/worker.html">worker</a></code>, <code class="module"><a href="../mod/prefork.html">prefork</a></code></td></tr>
 144 </table>
 145     <p>The <code class="directive">GracefulShutdownTimeout</code> specifies
 146     how many seconds after receiving a "graceful-stop" signal, a
 147     server should continue to run, handling the existing connections.</p>
 148
 149     <p>Setting this value to zero means that the server will wait
 150     indefinitely until all remaining requests have been fully served.</p>
 151
 152 </div>
 153 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 154 <div class="directive-section"><h2><a name="Listen" id="Listen">Listen</a> <a name="listen" id="listen">Directive</a></h2>
 155 <table class="directive">
 156 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>IP addresses and ports that the server
 157 listens to</td></tr>
 158 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>Listen [<var>IP-address</var>:]<var>portnumber</var> [<var>protocol</var>]</code></td></tr>
 159 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
 160 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
 161 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="../mod/event.html">event</a></code>, <code class="module"><a href="../mod/worker.html">worker</a></code>, <code class="module"><a href="../mod/prefork.html">prefork</a></code>, <code class="module"><a href="../mod/mpm_winnt.html">mpm_winnt</a></code>, <code class="module"><a href="../mod/mpm_netware.html">mpm_netware</a></code>, <code class="module"><a href="../mod/mpmt_os2.html">mpmt_os2</a></code></td></tr>
 162 </table>
 163     <p>The <code class="directive">Listen</code> directive instructs Apache httpd to
 164     listen to only specific IP addresses or ports; by default it
 165     responds to requests on all IP interfaces. <code class="directive">Listen</code>
 166     is now a required directive. If it is not in the config file, the
 167     server will fail to start. This is a change from previous versions
 168     of Apache httpd.</p>
 169
 170     <p>The <code class="directive">Listen</code> directive tells the server to
 171     accept incoming requests on the specified port or address-and-port
 172     combination. If only a port number is specified, the server listens to
 173     the given port on all interfaces. If an IP address is given as well
 174     as a port, the server will listen on the given port and
 175     interface.</p>
 176
 177     <p>Multiple <code class="directive">Listen</code> directives may be used to
 178     specify a number of addresses and ports to listen to. The server will
 179     respond to requests from any of the listed addresses and ports.</p>
 180
 181     <p>For example, to make the server accept connections on both
 182     port 80 and port 8000, use:</p>
 183
 184     <pre class="prettyprint lang-config">Listen 80
 185 Listen 8000</pre>
 186
 187
 188     <p>To make the server accept connections on two specified
 189     interfaces and port numbers, use </p>
 190
 191     <pre class="prettyprint lang-config">Listen 192.170.2.1:80
 192 Listen 192.170.2.5:8000</pre>
 193
 194
 195     <p>IPv6 addresses must be surrounded in square brackets, as in the
 196     following example:</p>
 197
 198     <pre class="prettyprint lang-config">Listen [2001:db8::a00:20ff:fea7:ccea]:80</pre>
 199
 200
 201     <p>The optional <var>protocol</var> argument is not required for most
 202        configurations. If not specified, <code>https</code> is the default for
 203        port 443 and <code>http</code> the default for all other ports.  The
 204        protocol is used to determine which module should handle a request, and
 205        to apply protocol specific optimizations with the
 206        <code class="directive"><a href="../mod/core.html#acceptfilter">AcceptFilter</a></code> directive.</p>
 207
 208     <p>You only need to set the protocol if you are running on non-standard
 209        ports.  For example, running an <code>https</code> site on port 8443:</p>
 210
 211     <pre class="prettyprint lang-config">Listen 192.170.2.1:8443 https</pre>
 212
 213
 214     <div class="note"><h3>Error condition</h3>
 215       Multiple <code class="directive">Listen</code> directives for the same ip
 216       address and port will result in an <code>Address already in use</code>
 217       error message.
 218     </div>
 219
 220
 221 <h3>See also</h3>
 222 <ul>
 223 <li><a href="../dns-caveats.html">DNS Issues</a></li>
 224 <li><a href="../bind.html">Setting which addresses and ports Apache HTTP Server
 225     uses</a></li>
 226 <li><a href="http://wiki.apache.org/httpd/CouldNotBindToAddress">Further
 227 discussion of the <code>Address already in use</code> error message,
 228 including other causes.</a></li>
 229 </ul>
 230 </div>
 231 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 232 <div class="directive-section"><h2><a name="ListenBackLog" id="ListenBackLog">ListenBackLog</a> <a name="listenbacklog" id="listenbacklog">Directive</a></h2>
 233 <table class="directive">
 234 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Maximum length of the queue of pending connections</td></tr>
 235 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ListenBacklog <var>backlog</var></code></td></tr>
 236 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>ListenBacklog 511</code></td></tr>
 237 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
 238 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
 239 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="../mod/event.html">event</a></code>, <code class="module"><a href="../mod/worker.html">worker</a></code>, <code class="module"><a href="../mod/prefork.html">prefork</a></code>, <code class="module"><a href="../mod/mpm_winnt.html">mpm_winnt</a></code>, <code class="module"><a href="../mod/mpm_netware.html">mpm_netware</a></code>, <code class="module"><a href="../mod/mpmt_os2.html">mpmt_os2</a></code></td></tr>
 240 </table>
 241     <p>The maximum length of the queue of pending connections.
 242     Generally no tuning is needed or desired, however on some
 243     systems it is desirable to increase this when under a TCP SYN
 244     flood attack. See the backlog parameter to the
 245     <code>listen(2)</code> system call.</p>
 246
 247     <p>This will often be limited to a smaller number by the
 248     operating system. This varies from OS to OS. Also note that
 249     many OSes do not use exactly what is specified as the backlog,
 250     but use a number based on (but normally larger than) what is
 251     set.</p>
 252
 253 </div>
 254 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 255 <div class="directive-section"><h2><a name="ListenCoresBucketsRatio" id="ListenCoresBucketsRatio">ListenCoresBucketsRatio</a> <a name="listencoresbucketsratio" id="listencoresbucketsratio">Directive</a></h2>
 256 <table class="directive">
 257 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Ratio between the number of CPU cores (online) and the number of
 258 listeners' buckets</td></tr>
 259 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ListenCoresBucketsRatio <var>ratio</var></code></td></tr>
 260 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>ListenCoresBucketsRatio 0 (disabled)</code></td></tr>
 261 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
 262 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
 263 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="../mod/event.html">event</a></code>, <code class="module"><a href="../mod/worker.html">worker</a></code>, <code class="module"><a href="../mod/prefork.html">prefork</a></code></td></tr>
 264 <tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in Apache HTTP Server 2.4.17, with a kernel supporting
 265 the socket option <code>SO_REUSEPORT</code> and distributing new connections
 266 evenly accross listening processes' (or threads') sockets using it (eg. Linux
 267 3.9 and later, but not the current implementations of <code>SO_REUSEPORT</code>
 268 in *BSDs.</td></tr>
 269 </table>
 270     <p>A <var>ratio</var> between the number of (online) CPU cores and the
 271     number of listeners' buckets can be used to make Apache HTTP Server create
 272     <code>num_cpu_cores / ratio</code> listening buckets, each containing its
 273     own <code class="directive">Listen</code>-ing socket(s) on the same port(s), and
 274     then make each child handle a single bucket (with round-robin distribution
 275     of the buckets at children creation time).</p>
 276
 277     <p><code class="directive">ListenCoresBucketsRatio</code> can improve the
 278     scalability when accepting new connections is/becomes the bottleneck.
 279     On systems with a large number of CPU cores, enabling this feature has
 280     been tested to show significant performances improvement and shorter
 281     responses time.</p>
 282
 283     <p>There must be at least twice the number of CPU cores than the
 284     configured <var>ratio</var> for this to be active. The recommended
 285     <var>ratio</var> is <code>8</code>, hence at least <code>16</code>
 286     cores should be available at runtime when this value is used.</p>
 287
 288 </div>
 289 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 290 <div class="directive-section"><h2><a name="MaxConnectionsPerChild" id="MaxConnectionsPerChild">MaxConnectionsPerChild</a> <a name="maxconnectionsperchild" id="maxconnectionsperchild">Directive</a></h2>
 291 <table class="directive">
 292 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Limit on the number of connections that an individual child server
 293 will handle during its life</td></tr>
 294 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MaxConnectionsPerChild <var>number</var></code></td></tr>
 295 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MaxConnectionsPerChild 0</code></td></tr>
 296 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
 297 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
 298 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="../mod/event.html">event</a></code>, <code class="module"><a href="../mod/worker.html">worker</a></code>, <code class="module"><a href="../mod/prefork.html">prefork</a></code>, <code class="module"><a href="../mod/mpm_winnt.html">mpm_winnt</a></code>, <code class="module"><a href="../mod/mpm_netware.html">mpm_netware</a></code>, <code class="module"><a href="../mod/mpmt_os2.html">mpmt_os2</a></code></td></tr>
 299 <tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available Apache HTTP Server 2.3.9 and later. The old name
 300 <code>MaxRequestsPerChild</code> is still supported.</td></tr>
 301 </table>
 302     <p>The <code class="directive">MaxConnectionsPerChild</code> directive sets
 303     the limit on the number of connections that an individual child
 304     server process will handle. After
 305     <code class="directive">MaxConnectionsPerChild</code> connections, the child
 306     process will die. If <code class="directive">MaxConnectionsPerChild</code> is
 307     <code>0</code>, then the process will never expire.</p>
 308
 309     <p>Setting <code class="directive">MaxConnectionsPerChild</code> to a
 310     non-zero value limits the amount of memory that process can consume
 311     by (accidental) memory leakage.</p>
 312
 313 </div>
 314 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 315 <div class="directive-section"><h2><a name="MaxMemFree" id="MaxMemFree">MaxMemFree</a> <a name="maxmemfree" id="maxmemfree">Directive</a></h2>
 316 <table class="directive">
 317 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Maximum amount of memory that the main allocator is allowed
 318 to hold without calling <code>free()</code></td></tr>
 319 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MaxMemFree <var>KBytes</var></code></td></tr>
 320 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MaxMemFree 2048</code></td></tr>
 321 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
 322 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
 323 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="../mod/event.html">event</a></code>, <code class="module"><a href="../mod/worker.html">worker</a></code>, <code class="module"><a href="../mod/prefork.html">prefork</a></code>, <code class="module"><a href="../mod/mpm_winnt.html">mpm_winnt</a></code>, <code class="module"><a href="../mod/mpm_netware.html">mpm_netware</a></code></td></tr>
 324 </table>
 325     <p>The <code class="directive">MaxMemFree</code> directive sets the
 326     maximum number of free Kbytes that every allocator is allowed
 327     to hold without calling <code>free()</code>. In threaded MPMs, every
 328     thread has its own allocator. When set
 329     to zero, the threshold will be set to unlimited.</p>
 330
 331 </div>
 332 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 333 <div class="directive-section"><h2><a name="MaxRequestWorkers" id="MaxRequestWorkers">MaxRequestWorkers</a> <a name="maxrequestworkers" id="maxrequestworkers">Directive</a></h2>
 334 <table class="directive">
 335 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Maximum number of connections that will be processed
 336 simultaneously</td></tr>
 337 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MaxRequestWorkers <var>number</var></code></td></tr>
 338 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>See usage for details</code></td></tr>
 339 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
 340 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
 341 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="../mod/event.html">event</a></code>, <code class="module"><a href="../mod/worker.html">worker</a></code>, <code class="module"><a href="../mod/prefork.html">prefork</a></code></td></tr>
 342 </table>
 343     <p>The <code class="directive">MaxRequestWorkers</code> directive sets the limit
 344     on the number of simultaneous requests that will be served.  Any
 345     connection attempts over the <code class="directive">MaxRequestWorkers</code>
 346     limit will normally be queued, up to a number based on the
 347     <code class="directive"><a href="#listenbacklog">ListenBacklog</a></code>
 348     directive. Once a child process is freed at the end of a different
 349     request, the connection will then be serviced.</p>
 350
 351     <p>For non-threaded servers (<em>i.e.</em>, <code class="module"><a href="../mod/prefork.html">prefork</a></code>),
 352     <code class="directive">MaxRequestWorkers</code> translates into the maximum
 353     number of child processes that will be launched to serve requests.
 354     The default value is <code>256</code>; to increase it, you must also raise
 355     <code class="directive"><a href="#serverlimit">ServerLimit</a></code>.</p>
 356
 357     <p>For threaded and hybrid servers (<em>e.g.</em> <code class="module"><a href="../mod/event.html">event</a></code>
 358     or <code class="module"><a href="../mod/worker.html">worker</a></code>) <code class="directive">MaxRequestWorkers</code> restricts
 359     the total number of threads that will be available to serve clients.
 360     For hybrid MPMs the default value is <code>16</code> (<code class="directive"><a href="#serverlimit">ServerLimit</a></code>) multiplied by the value of
 361     <code>25</code> (<code class="directive"><a href="#threadsperchild">ThreadsPerChild</a></code>). Therefore, to increase <code class="directive">MaxRequestWorkers</code> to a value that requires more than 16 processes,
 362     you must also raise <code class="directive"><a href="#serverlimit">ServerLimit</a></code>.</p>
 363
 364     <p><code class="directive">MaxRequestWorkers</code> was called
 365     <code class="directive">MaxClients</code> before version 2.3.13. The old name is still
 366     supported.</p>
 367
 368 </div>
 369 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 370 <div class="directive-section"><h2><a name="MaxSpareThreads" id="MaxSpareThreads">MaxSpareThreads</a> <a name="maxsparethreads" id="maxsparethreads">Directive</a></h2>
 371 <table class="directive">
 372 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Maximum number of idle threads</td></tr>
 373 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MaxSpareThreads <var>number</var></code></td></tr>
 374 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>See usage for details</code></td></tr>
 375 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
 376 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
 377 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="../mod/event.html">event</a></code>, <code class="module"><a href="../mod/worker.html">worker</a></code>, <code class="module"><a href="../mod/mpm_netware.html">mpm_netware</a></code>, <code class="module"><a href="../mod/mpmt_os2.html">mpmt_os2</a></code></td></tr>
 378 </table>
 379     <p>Maximum number of idle threads. Different MPMs deal with this
 380     directive differently.</p>
 381
 382     <p>For <code class="module"><a href="../mod/worker.html">worker</a></code> and <code class="module"><a href="../mod/event.html">event</a></code>, the default is
 383     <code>MaxSpareThreads 250</code>. These MPMs deal with idle threads
 384     on a server-wide basis. If there are too many idle threads in the
 385     server then child processes are killed until the number of idle
 386     threads is less than this number.</p>
 387
 388     <p>For <code class="module"><a href="../mod/mpm_netware.html">mpm_netware</a></code> the default is
 389     <code>MaxSpareThreads 100</code>. Since this MPM runs a
 390     single-process, the spare thread count is also server-wide.</p>
 391
 392     <p><code class="module"><a href="../mod/mpmt_os2.html">mpmt_os2</a></code> works
 393     similar to <code class="module"><a href="../mod/mpm_netware.html">mpm_netware</a></code>. For
 394     <code class="module"><a href="../mod/mpmt_os2.html">mpmt_os2</a></code> the default value is <code>10</code>.</p>
 395
 396     <div class="note"><h3>Restrictions</h3>
 397       <p>The range of the <code class="directive">MaxSpareThreads</code> value
 398       is restricted. Apache httpd will correct the given value automatically
 399       according to the following rules:</p>
 400       <ul>
 401         <li><code class="module"><a href="../mod/mpm_netware.html">mpm_netware</a></code> wants the value to be greater than
 402         <code class="directive"><a href="#minsparethreads">MinSpareThreads</a></code>.</li>
 403
 404         <li>For <code class="module"><a href="../mod/worker.html">worker</a></code> and <code class="module"><a href="../mod/event.html">event</a></code>, the value
 405         must be greater or equal to the sum of <code class="directive"><a href="#minsparethreads">
 406         MinSpareThreads</a></code> and <code class="directive"><a href="#threadsperchild">
 407         ThreadsPerChild</a></code>.</li>
 408       </ul>
 409     </div>
 410
 411 <h3>See also</h3>
 412 <ul>
 413 <li><code class="directive"><a href="#minsparethreads">MinSpareThreads</a></code></li>
 414 <li><code class="directive"><a href="#startservers">StartServers</a></code></li>
 415 <li><code class="directive"><a href="../mod/prefork.html#maxspareservers">MaxSpareServers</a></code></li>
 416 </ul>
 417 </div>
 418 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 419 <div class="directive-section"><h2><a name="MinSpareThreads" id="MinSpareThreads">MinSpareThreads</a> <a name="minsparethreads" id="minsparethreads">Directive</a></h2>
 420 <table class="directive">
 421 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Minimum number of idle threads available to handle request
 422 spikes</td></tr>
 423 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MinSpareThreads <var>number</var></code></td></tr>
 424 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>See usage for details</code></td></tr>
 425 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
 426 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
 427 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="../mod/event.html">event</a></code>, <code class="module"><a href="../mod/worker.html">worker</a></code>, <code class="module"><a href="../mod/mpm_netware.html">mpm_netware</a></code>, <code class="module"><a href="../mod/mpmt_os2.html">mpmt_os2</a></code></td></tr>
 428 </table>
 429     <p>Minimum number of idle threads to handle request spikes.
 430     Different MPMs deal with this directive differently.</p>
 431
 432     <p><code class="module"><a href="../mod/worker.html">worker</a></code> and <code class="module"><a href="../mod/event.html">event</a></code> use a default of
 433     <code>MinSpareThreads 75</code> and deal with idle threads on a server-wide
 434     basis. If there aren't enough idle threads in the server then child
 435     processes are created until the number of idle threads is greater
 436     than <var>number</var>.</p>
 437
 438     <p><code class="module"><a href="../mod/mpm_netware.html">mpm_netware</a></code> uses a default of
 439     <code>MinSpareThreads 10</code> and, since it is a single-process
 440     MPM, tracks this on a server-wide bases.</p>
 441
 442     <p><code class="module"><a href="../mod/mpmt_os2.html">mpmt_os2</a></code> works
 443     similar to <code class="module"><a href="../mod/mpm_netware.html">mpm_netware</a></code>.  For
 444     <code class="module"><a href="../mod/mpmt_os2.html">mpmt_os2</a></code> the default value is <code>5</code>.</p>
 445
 446 <h3>See also</h3>
 447 <ul>
 448 <li><code class="directive"><a href="#maxsparethreads">MaxSpareThreads</a></code></li>
 449 <li><code class="directive"><a href="#startservers">StartServers</a></code></li>
 450 <li><code class="directive"><a href="../mod/prefork.html#minspareservers">MinSpareServers</a></code></li>
 451 </ul>
 452 </div>
 453 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 454 <div class="directive-section"><h2><a name="PidFile" id="PidFile">PidFile</a> <a name="pidfile" id="pidfile">Directive</a></h2>
 455 <table class="directive">
 456 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>File where the server records the process ID
 457 of the daemon</td></tr>
 458 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>PidFile <var>filename</var></code></td></tr>
 459 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>PidFile httpd.pid</code></td></tr>
 460 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
 461 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
 462 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="../mod/event.html">event</a></code>, <code class="module"><a href="../mod/worker.html">worker</a></code>, <code class="module"><a href="../mod/prefork.html">prefork</a></code>, <code class="module"><a href="../mod/mpm_winnt.html">mpm_winnt</a></code>, <code class="module"><a href="../mod/mpmt_os2.html">mpmt_os2</a></code></td></tr>
 463 </table>
 464     <p>The <code class="directive">PidFile</code> directive sets the file to
 465     which the server records the process id of the daemon. If the
 466     filename is not absolute then it is assumed to be relative to the
 467     <code class="directive"><a href="../mod/core.html#defaultruntimedir">DefaultRuntimeDir</a></code>.</p>
 468
 469     <div class="example"><h3>Example</h3><pre class="prettyprint lang-config">PidFile /var/run/apache.pid</pre>
 470 </div>
 471
 472     <p>It is often useful to be able to send the server a signal,
 473     so that it closes and then re-opens its <code class="directive"><a href="../mod/core.html#errorlog">ErrorLog</a></code> and <code class="directive"><a href="../mod/mod_log_config.html#transferlog">TransferLog</a></code>, and
 474     re-reads its configuration files. This is done by sending a
 475     SIGHUP (kill -1) signal to the process id listed in the
 476     <code class="directive">PidFile</code>.</p>
 477
 478     <p>The <code class="directive">PidFile</code> is subject to the same
 479     warnings about log file placement and <a href="../misc/security_tips.html#serverroot">security</a>.</p>
 480
 481     <div class="note"><h3>Note</h3>
 482       <p>As of Apache HTTP Server 2, we recommended that you only use the <code class="program"><a href="../programs/apachectl.html">apachectl</a></code> script, or the init script that your OS provides,
 483       for (re-)starting or stopping the server.</p>
 484     </div>
 485
 486 </div>
 487 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 488 <div class="directive-section"><h2><a name="ReceiveBufferSize" id="ReceiveBufferSize">ReceiveBufferSize</a> <a name="receivebuffersize" id="receivebuffersize">Directive</a></h2>
 489 <table class="directive">
 490 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>TCP receive buffer size</td></tr>
 491 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ReceiveBufferSize <var>bytes</var></code></td></tr>
 492 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>ReceiveBufferSize 0</code></td></tr>
 493 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
 494 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
 495 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="../mod/event.html">event</a></code>, <code class="module"><a href="../mod/worker.html">worker</a></code>, <code class="module"><a href="../mod/prefork.html">prefork</a></code>, <code class="module"><a href="../mod/mpm_winnt.html">mpm_winnt</a></code>, <code class="module"><a href="../mod/mpm_netware.html">mpm_netware</a></code>, <code class="module"><a href="../mod/mpmt_os2.html">mpmt_os2</a></code></td></tr>
 496 </table>
 497     <p>The server will set the TCP receive buffer size to the number of
 498     bytes specified.</p>
 499
 500     <p>If set to the value of <code>0</code>, the server will use the
 501     OS default.</p>
 502
 503 </div>
 504 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 505 <div class="directive-section"><h2><a name="ScoreBoardFile" id="ScoreBoardFile">ScoreBoardFile</a> <a name="scoreboardfile" id="scoreboardfile">Directive</a></h2>
 506 <table class="directive">
 507 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Location of the file used to store coordination data for
 508 the child processes</td></tr>
 509 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ScoreBoardFile <var>file-path</var></code></td></tr>
 510 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>ScoreBoardFile apache_runtime_status</code></td></tr>
 511 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
 512 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
 513 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="../mod/event.html">event</a></code>, <code class="module"><a href="../mod/worker.html">worker</a></code>, <code class="module"><a href="../mod/prefork.html">prefork</a></code>, <code class="module"><a href="../mod/mpm_winnt.html">mpm_winnt</a></code></td></tr>
 514 </table>
 515     <p>Apache HTTP Server uses a scoreboard to communicate between its parent
 516     and child processes.  Some architectures require a file to facilitate
 517     this communication. If the file is left unspecified, Apache httpd first
 518     attempts to create the scoreboard entirely in memory (using anonymous
 519     shared memory) and, failing that, will attempt to create the file on
 520     disk (using file-based shared memory). Specifying this directive causes
 521     Apache httpd to always create the file on the disk.</p>
 522
 523     <p>If <var>file-path</var> is not an absolute path, the location specified
 524     will be relative to the value of
 525     <code class="directive"><a href="../mod/core.html#defaultruntimedir">DefaultRuntimeDir</a></code>.</p>
 526
 527     <div class="example"><h3>Example</h3><pre class="prettyprint lang-config">ScoreBoardFile /var/run/apache_runtime_status</pre>
 528 </div>
 529
 530     <p>File-based shared memory is useful for third-party applications
 531     that require direct access to the scoreboard.</p>
 532
 533     <p>If you use a <code class="directive">ScoreBoardFile</code> then
 534     you may see improved speed by placing it on a RAM disk. But be
 535     careful that you heed the same warnings about log file placement
 536     and <a href="../misc/security_tips.html">security</a>.</p>
 537
 538 <h3>See also</h3>
 539 <ul>
 540 <li><a href="../stopping.html">Stopping and Restarting
 541 Apache HTTP Server</a></li>
 542 </ul>
 543 </div>
 544 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 545 <div class="directive-section"><h2><a name="SendBufferSize" id="SendBufferSize">SendBufferSize</a> <a name="sendbuffersize" id="sendbuffersize">Directive</a></h2>
 546 <table class="directive">
 547 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>TCP buffer size</td></tr>
 548 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>SendBufferSize <var>bytes</var></code></td></tr>
 549 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>SendBufferSize 0</code></td></tr>
 550 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
 551 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
 552 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="../mod/event.html">event</a></code>, <code class="module"><a href="../mod/worker.html">worker</a></code>, <code class="module"><a href="../mod/prefork.html">prefork</a></code>, <code class="module"><a href="../mod/mpm_winnt.html">mpm_winnt</a></code>, <code class="module"><a href="../mod/mpm_netware.html">mpm_netware</a></code>, <code class="module"><a href="../mod/mpmt_os2.html">mpmt_os2</a></code></td></tr>
 553 </table>
 554     <p>Sets the server's TCP send buffer size to the number of bytes
 555     specified. It is often useful to set this past the OS's standard
 556     default value on high speed, high latency connections
 557     (<em>i.e.</em>, 100ms or so, such as transcontinental fast pipes).</p>
 558
 559     <p>If set to the value of <code>0</code>, the server will use the
 560     default value provided by your OS.</p>
 561
 562     <p>Further configuration of your operating system may be required to elicit
 563     better performance on high speed, high latency connections.</p>
 564
 565     <div class="note"> <p> On some operating systems, changes in TCP behavior resulting
 566     from a larger <code class="directive">SendBufferSize</code> may not be seen unless
 567     <code class="directive"><a href="../mod/core.html#enablesendfile">EnableSendfile</a></code> is set to OFF.  This
 568     interaction applies only to static files.</p> </div>
 569
 570
 571 </div>
 572 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 573 <div class="directive-section"><h2><a name="ServerLimit" id="ServerLimit">ServerLimit</a> <a name="serverlimit" id="serverlimit">Directive</a></h2>
 574 <table class="directive">
 575 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Upper limit on configurable number of processes</td></tr>
 576 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ServerLimit <var>number</var></code></td></tr>
 577 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>See usage for details</code></td></tr>
 578 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
 579 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
 580 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="../mod/event.html">event</a></code>, <code class="module"><a href="../mod/worker.html">worker</a></code>, <code class="module"><a href="../mod/prefork.html">prefork</a></code></td></tr>
 581 </table>
 582     <p>For the <code class="module"><a href="../mod/prefork.html">prefork</a></code> MPM, this directive sets the
 583     maximum configured value for <code class="directive"><a href="#maxrequestworkers">MaxRequestWorkers</a></code> for the lifetime of the
 584     Apache httpd process. For the <code class="module"><a href="../mod/worker.html">worker</a></code> and <code class="module"><a href="../mod/event.html">event
 585     </a></code> MPMs, this directive in combination with <code class="directive"><a href="#threadlimit">ThreadLimit</a></code> sets
 586     the maximum configured value for <code class="directive"><a href="#maxrequestworkers">MaxRequestWorkers</a></code> for the lifetime of the
 587     Apache httpd process. Any attempts to change this directive during a
 588     restart will be ignored, but <code class="directive"><a href="#maxrequestworkers">MaxRequestWorkers</a></code> can be modified during
 589     a restart.</p>
 590
 591     <p>Special care must be taken when using this directive.  If
 592     <code class="directive">ServerLimit</code> is set to a value much higher
 593     than necessary, extra, unused shared memory will be allocated.  If
 594     both <code class="directive">ServerLimit</code> and <code class="directive"><a href="#maxrequestworkers">MaxRequestWorkers</a></code> are set to values
 595     higher than the system can handle, Apache httpd may not start or the
 596     system may become unstable.</p>
 597
 598     <p>With the <code class="module"><a href="../mod/prefork.html">prefork</a></code> MPM, use this directive only
 599     if you need to set <code class="directive"><a href="#maxrequestworkers">MaxRequestWorkers</a></code> higher than 256 (default).
 600     Do not set the value of this directive any higher than what you
 601     might want to set <code class="directive"><a href="#maxrequestworkers">MaxRequestWorkers</a></code> to.</p>
 602
 603     <p>With <code class="module"><a href="../mod/worker.html">worker</a></code> and <code class="module"><a href="../mod/event.html">event</a></code>, use this
 604     directive only if your <code class="directive"><a href="#maxrequestworkers">MaxRequestWorkers
 605     </a></code> and <code class="directive"><a href="#threadsperchild">ThreadsPerChild</a></code>
 606     settings require more than 16 server processes (default). Do not set
 607     the value of this directive any higher than the number of server
 608     processes required by what you may want for <code class="directive"><a href="#maxrequestworkers">MaxRequestWorkers </a></code> and <code class="directive"><a href="#threadsperchild">ThreadsPerChild</a></code>.</p>
 609
 610     <div class="note"><h3>Note</h3>
 611       <p>There is a hard limit of <code>ServerLimit 20000</code> compiled
 612       into the server (for the <code class="module"><a href="../mod/prefork.html">prefork</a></code> MPM 200000). This is
 613       intended to avoid nasty effects caused by typos. To increase it
 614       even further past this limit, you will need to modify the value of
 615       MAX_SERVER_LIMIT in the mpm source file and rebuild the server.</p>
 616     </div>
 617
 618 <h3>See also</h3>
 619 <ul>
 620 <li><a href="../stopping.html">Stopping and Restarting Apache HTTP Server</a></li>
 621 </ul>
 622 </div>
 623 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 624 <div class="directive-section"><h2><a name="StartServers" id="StartServers">StartServers</a> <a name="startservers" id="startservers">Directive</a></h2>
 625 <table class="directive">
 626 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Number of child server processes created at startup</td></tr>
 627 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>StartServers <var>number</var></code></td></tr>
 628 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>See usage for details</code></td></tr>
 629 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
 630 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
 631 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="../mod/event.html">event</a></code>, <code class="module"><a href="../mod/worker.html">worker</a></code>, <code class="module"><a href="../mod/prefork.html">prefork</a></code>, <code class="module"><a href="../mod/mpmt_os2.html">mpmt_os2</a></code></td></tr>
 632 </table>
 633     <p>The <code class="directive">StartServers</code> directive sets the
 634     number of child server processes created on startup. As the number
 635     of processes is dynamically controlled depending on the load, (see
 636     <code class="directive"><a href="#minsparethreads">MinSpareThreads</a></code>,
 637     <code class="directive"><a href="#maxsparethreads">MaxSpareThreads</a></code>,
 638     <code class="directive"><a href="../mod/prefork.html#minspareservers">MinSpareServers</a></code>, <code class="directive"><a href="../mod/prefork.html#maxspareservers">MaxSpareServers</a></code>)
 639     there is usually little reason to adjust this parameter.</p>
 640
 641     <p>The default value differs from MPM to MPM. <code class="module"><a href="../mod/worker.html">worker</a></code> and
 642     <code class="module"><a href="../mod/event.html">event</a></code> default to <code>StartServers 3</code>; <code class="module"><a href="../mod/prefork.html">
 643     prefork</a></code> defaults to <code>5</code>; <code class="module"><a href="../mod/mpmt_os2.html">mpmt_os2</a></code>
 644     defaults to <code>2</code>.</p>
 645
 646 </div>
 647 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 648 <div class="directive-section"><h2><a name="StartThreads" id="StartThreads">StartThreads</a> <a name="startthreads" id="startthreads">Directive</a></h2>
 649 <table class="directive">
 650 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Number of threads created on startup</td></tr>
 651 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>StartThreads <var>number</var></code></td></tr>
 652 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>See usage for details</code></td></tr>
 653 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
 654 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
 655 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="../mod/mpm_netware.html">mpm_netware</a></code></td></tr>
 656 </table>
 657     <p>Number of threads created on startup. As the
 658     number of threads is dynamically controlled depending on the
 659     load, (see
 660     <code class="directive"><a href="#minsparethreads">MinSpareThreads</a></code>,
 661     <code class="directive"><a href="#maxsparethreads">MaxSpareThreads</a></code>,
 662     <code class="directive"><a href="../mod/prefork.html#minspareservers">MinSpareServers</a></code>, <code class="directive"><a href="../mod/prefork.html#maxspareservers">MaxSpareServers</a></code>)
 663     there is usually little reason to adjust this
 664     parameter.</p>
 665
 666     <p>For <code class="module"><a href="../mod/mpm_netware.html">mpm_netware</a></code> the default is
 667     <code>StartThreads 50</code> and, since there is only a single
 668     process, this is the total number of threads created at startup to
 669     serve requests.</p>
 670
 671 </div>
 672 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 673 <div class="directive-section"><h2><a name="ThreadLimit" id="ThreadLimit">ThreadLimit</a> <a name="threadlimit" id="threadlimit">Directive</a></h2>
 674 <table class="directive">
 675 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Sets the upper limit on the configurable number of threads
 676 per child process</td></tr>
 677 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ThreadLimit <var>number</var></code></td></tr>
 678 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>See usage for details</code></td></tr>
 679 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
 680 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
 681 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="../mod/event.html">event</a></code>, <code class="module"><a href="../mod/worker.html">worker</a></code>, <code class="module"><a href="../mod/mpm_winnt.html">mpm_winnt</a></code></td></tr>
 682 </table>
 683     <p>This directive sets the maximum configured value for <code class="directive"><a href="#threadsperchild">ThreadsPerChild</a></code> for the lifetime
 684     of the Apache httpd process.  Any attempts to change this directive
 685     during a restart will be ignored, but <code class="directive"><a href="#threadsperchild">ThreadsPerChild</a></code> can be modified
 686     during a restart up to the value of this directive.</p>
 687
 688     <p>Special care must be taken when using this directive.  If
 689     <code class="directive">ThreadLimit</code> is set to a value much higher
 690     than <code class="directive"><a href="#threadsperchild">ThreadsPerChild</a></code>,
 691     extra unused shared memory will be allocated.  If both
 692     <code class="directive">ThreadLimit</code> and <code class="directive"><a href="#threadsperchild">ThreadsPerChild</a></code> are set to values
 693     higher than the system can handle, Apache httpd may not start or the
 694     system may become unstable. Do not set the value of this directive
 695     any higher than your greatest predicted setting of <code class="directive"><a href="#threadsperchild">ThreadsPerChild</a></code> for the
 696     current run of Apache httpd.</p>
 697
 698     <p>The default value for <code class="directive">ThreadLimit</code> is
 699     <code>1920</code> when used with <code class="module"><a href="../mod/mpm_winnt.html">mpm_winnt</a></code> and
 700     <code>64</code> when used with the others.</p>
 701
 702     <div class="note"><h3>Note</h3>
 703       <p>There is a hard limit of <code>ThreadLimit 20000</code> (or
 704       <code>ThreadLimit 100000</code> with <code class="module"><a href="../mod/event.html">event</a></code>,
 705       <code>ThreadLimit 15000</code> with <code class="module"><a href="../mod/mpm_winnt.html">mpm_winnt</a></code>)
 706       compiled into the server. This is intended to avoid nasty effects
 707       caused by typos. To increase it even further past this limit, you
 708       will need to modify the value of MAX_THREAD_LIMIT in the mpm
 709       source file and rebuild the server.</p>
 710     </div>
 711
 712 </div>
 713 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 714 <div class="directive-section"><h2><a name="ThreadsPerChild" id="ThreadsPerChild">ThreadsPerChild</a> <a name="threadsperchild" id="threadsperchild">Directive</a></h2>
 715 <table class="directive">
 716 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Number of threads created by each child process</td></tr>
 717 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ThreadsPerChild <var>number</var></code></td></tr>
 718 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>See usage for details</code></td></tr>
 719 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
 720 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
 721 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="../mod/event.html">event</a></code>, <code class="module"><a href="../mod/worker.html">worker</a></code>, <code class="module"><a href="../mod/mpm_winnt.html">mpm_winnt</a></code></td></tr>
 722 </table>
 723     <p>This directive sets the number of threads created by each
 724     child process. The child creates these threads at startup and
 725     never creates more. If using an MPM like <code class="module"><a href="../mod/mpm_winnt.html">mpm_winnt</a></code>,
 726     where there is only one child process, this number should be high
 727     enough to handle the entire load of the server. If using an MPM
 728     like <code class="module"><a href="../mod/worker.html">worker</a></code>, where there are multiple child processes,
 729     the <em>total</em> number of threads should be high enough to handle
 730     the common load on the server.</p>
 731
 732     <p>The default value for <code class="directive">ThreadsPerChild</code> is
 733     <code>64</code> when used with <code class="module"><a href="../mod/mpm_winnt.html">mpm_winnt</a></code> and
 734     <code>25</code> when used with the others.</p>
 735
 736 </div>
 737 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 738 <div class="directive-section"><h2><a name="ThreadStackSize" id="ThreadStackSize">ThreadStackSize</a> <a name="threadstacksize" id="threadstacksize">Directive</a></h2>
 739 <table class="directive">
 740 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The size in bytes of the stack used by threads handling
 741 client connections</td></tr>
 742 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ThreadStackSize <var>size</var></code></td></tr>
 743 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>65536 on NetWare; varies on other operating systems</code></td></tr>
 744 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
 745 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
 746 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td><code class="module"><a href="../mod/event.html">event</a></code>, <code class="module"><a href="../mod/worker.html">worker</a></code>, <code class="module"><a href="../mod/mpm_winnt.html">mpm_winnt</a></code>, <code class="module"><a href="../mod/mpm_netware.html">mpm_netware</a></code>, <code class="module"><a href="../mod/mpmt_os2.html">mpmt_os2</a></code></td></tr>
 747 </table>
 748     <p>The <code class="directive">ThreadStackSize</code> directive sets the
 749     size of the stack (for autodata) of threads which handle client
 750     connections and call modules to help process those connections.
 751     In most cases the operating system default for stack size is
 752     reasonable, but there are some conditions where it may need to be
 753     adjusted:</p>
 754
 755     <ul>
 756       <li>On platforms with a relatively small default thread stack size
 757       (e.g., HP-UX), Apache httpd may crash when using some third-party modules
 758       which use a relatively large amount of autodata storage.  Those
 759       same modules may have worked fine on other platforms where the
 760       default thread stack size is larger.  This type of crash is
 761       resolved by setting <code class="directive">ThreadStackSize</code> to a
 762       value higher than the operating system default.  This type of
 763       adjustment is necessary only if the provider of the third-party
 764       module specifies that it is required, or if diagnosis of an Apache httpd
 765       crash indicates that the thread stack size was too small.</li>
 766
 767       <li>On platforms where the default thread stack size is
 768       significantly larger than necessary for the web server
 769       configuration, a higher number of threads per child process
 770       will be achievable if <code class="directive">ThreadStackSize</code> is
 771       set to a value lower than the operating system default.  This type
 772       of adjustment should only be made in a test environment which allows
 773       the full set of web server processing can be exercised, as there
 774       may be infrequent requests which require more stack to process.
 775       The minimum required stack size strongly depends on the modules
 776       used, but any change in the web server configuration can invalidate
 777       the current <code class="directive">ThreadStackSize</code> setting.</li>
 778
 779       <li>On Linux, this directive can only be used to increase the default
 780       stack size, as the underlying system call uses the value as a
 781       <em>minimum</em> stack size.  The (often large) soft limit for
 782       <code>ulimit -s</code> (8MB if unlimited) is used as the default stack
 783       size.</li>
 784     </ul>
 785
 786     <div class="note">It is recommended to not reduce <code class="directive">ThreadStackSize</code>
 787     unless a high number of threads per child process is needed. On some
 788     platforms (including Linux), a setting of 128000 is already too low and
 789     causes crashes with some common modules.</div>
 790
 791 </div>
 792 </div>
 793 <div class="bottomlang">
 794 <p><span>Available Languages: </span><a href="../de/mod/mpm_common.html" hreflang="de" rel="alternate" title="Deutsch">&nbsp;de&nbsp;</a> |
 795 <a href="../en/mod/mpm_common.html" title="English">&nbsp;en&nbsp;</a> |
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 798 </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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