more than one multi-processing module (MPM)</description>
<status>MPM</status>
+<directivesynopsis>
+<name>AcceptMutex</name>
+<description>Method that Apache uses to serialize multiple children
+accepting requests on network sockets</description>
+<syntax>AcceptMutex Default|<var>method</var></syntax>
+<default>AcceptMutex Default</default>
+<contextlist><context>server config</context></contextlist>
+<modulelist><module>leader</module><module>perchild</module>
+<module>prefork</module><module>threadpool</module><module>worker</module>
+</modulelist>
+
+<usage>
+ <p>The <directive>AcceptMutex</directive> directives sets the
+ method that Apache uses to serialize multiple children accepting
+ requests on network sockets. Prior to Apache 2.0, the method was
+ selectable only at compile time. The optimal method to use is
+ highly architecture and platform dependent. For further details,
+ see the <a href="../misc/perf-tuning.html">performance tuning</a>
+ documentation.</p>
+
+ <p>If this directive is set to <code>Default</code>, then the
+ compile-time selected default will be used. Other possible
+ methods are listed below. Note that not all methods are
+ available on all platforms. If a method is specified which is
+ not available, a message will be written to the error log
+ listing the available methods.</p>
+
+ <dl>
+ <dt><code>flock</code></dt>
+ <dd>uses the <code>flock(2)</code> system call to lock the
+ file defined by the <directive module="mpm_common"
+ >LockFile</directive> directive.</dd>
+
+ <dt><code>fcntl</code></dt>
+ <dd>uses the <code>fnctl(2)</code> system call to lock the
+ file defined by the <directive module="mpm_common"
+ >LockFile</directive> directive.</dd>
+
+ <dt><code>posixsem</code></dt>
+ <dd>uses POSIX compatible semaphores to implement the mutex.</dd>
+
+ <dt><code>pthread</code></dt>
+ <dd>uses POSIX mutexes as implemented by the POSIX Threads
+ (PThreads) specification.</dd>
+
+ <dt><code>sysvsem</code></dt>
+ <dd>uses SySV-style semaphores to implement the mutex.</dd>
+ </dl>
+
+ <p>If you want to find out the compile time chosen default
+ for your system, you may set your <directive module="core"
+ >LogLevel</directive> to <code>debug</code>. Then the default <directive
+ >AcceptMutex</directive> will be written into the <directive
+ module="core">ErrorLog</directive>.</p>
+</usage>
+</directivesynopsis>
+
+<directivesynopsis>
+<name>BS2000Account</name>
+<description>Define the non-privileged account on BS2000
+machines</description>
+<syntax>BS2000Account <var>account</var></syntax>
+<contextlist><context>server config</context></contextlist>
+<modulelist><module>perchild</module><module>prefork</module></modulelist>
+<compatibility>Only available for BS2000 machines</compatibility>
+
+<usage>
+ <p>The <directive>BS2000Account</directive> directive is available for
+ BS2000 hosts only. It must be used to define the account number for
+ the non-privileged apache server user (which was configured using the
+ <directive module="mpm_common">User</directive> directive). This is
+ required by the BS2000 POSIX subsystem (to change the underlying BS2000
+ task environment by performing a sub-LOGON) to prevent CGI scripts
+ from accessing resources of the privileged account which started the
+ server, usually <code>SYSROOT</code>.</p>
+
+ <note><title>Note</title>
+ <p>Only one <code>BS2000Account</code> directive can be used.</p>
+ </note>
+</usage>
+<seealso><a href="../platform/ebcdic.html">Apache EBCDIC port</a></seealso>
+</directivesynopsis>
+
<directivesynopsis>
<name>CoreDumpDirectory</name>
<description>Directory where Apache attempts to
<syntax>CoreDumpDirectory <var>directory</var></syntax>
<default>See usage for the default setting</default>
<contextlist><context>server config</context></contextlist>
-<modulelist><module>worker</module><module>perchild</module>
-<module>prefork</module><module>mpm_winnt</module>
-</modulelist>
+<modulelist><module>beos</module><module>leader</module>
+<module>mpm_winnt</module><module>perchild</module><module>prefork</module>
+<module>threadpool</module><module>worker</module></modulelist>
<usage>
-
<p>This controls the directory to which Apache attempts to
switch before dumping core. The default is in the
<directive module="core">ServerRoot</directive> directory, however
requests</description>
<syntax>Group <var>unix-group</var></syntax>
<default>Group #-1</default>
-<contextlist><context>server config</context><context>virtual host</context>
-</contextlist>
-<modulelist><module>worker</module><module>perchild</module>
-<module>prefork</module></modulelist>
+<contextlist><context>server config</context></contextlist>
+<modulelist><module>beos</module><module>leader</module>
+<module>mpmt_os2</module><module>perchild</module><module>prefork</module>
+<module>threadpool</module><module>worker</module></modulelist>
+<compatibility>Only valid in global server config since Apache
+2.0</compatibility>
<usage>
<p>The <directive>Group</directive> directive sets the group under
which the server will answer requests. In order to use this
- directive, the stand-alone server must be run initially as root.
- <var>Unix-group</var> is one of:</p>
+ directive, the server must be run initially as root. If you start the
+ server as a non-root user, it will fail to change to the specified
+ group, and will instead continue to run as the group of the original
+ user. <var>Unix-group</var> is one of:</p>
<dl>
<dt>A group name</dt>
-
<dd>Refers to the given group by name.</dd>
- <dt># followed by a group number.</dt>
-
+ <dt><code>#</code> followed by a group number.</dt>
<dd>Refers to a group by its number.</dd>
</dl>
+
+ <example><title>Example</title>
+ Group www-group
+ </example>
+
<p>It is recommended that you set up a new group specifically for
running the server. Some admins use user <code>nobody</code>,
but this is not always possible or desirable.</p>
- <example>Group www-group</example>
+ <note type="warning"><title>Security</title>
+ <p>Don't set <directive>Group</directive> (or <directive
+ module="mpm_common">User</directive>) to <code>root</code> unless
+ you know exactly what you are doing, and what the dangers are.</p>
+ </note>
- <p>Note: if you start the server as a non-root user, it will
- fail to change to the specified group, and will instead
- continue to run as the group of the original user.</p>
+ <p>Special note: Use of this directive in <directive module="core"
+ type="section">VirtualHost</directive> is no longer supported. To
+ configure your server for <a href="mod_suexec.html">suexec</a> use
+ <directive module="mod_suexec">SuexecUserGroup</directive>.</p>
- <p>Special note: Use of this directive in <VirtualHost> is
- no longer supported. To implement the <a
- href="../suexec.html">suEXEC wrapper</a> with Apache 2.0, use the
- <directive module="mod_suexec">SuexecUserGroup</directive>
- directive. SECURITY: See <directive
- module="mpm_common">User</directive> for a discussion of the
- security considerations.</p>
+ <note><title>Note</title>
+ <p>Although the <directive>Group</directive> directive is present
+ in the <module>beos</module> and <module>mpmt_os2</module> MPMs,
+ it is actually a no-op there and only exists for compatibility
+ reasons.</p>
+ </note>
</usage>
</directivesynopsis>
<syntax>PidFile <var>filename</var></syntax>
<default>PidFile logs/httpd.pid</default>
<contextlist><context>server config</context></contextlist>
-<modulelist><module>worker</module><module>perchild</module>
-<module>prefork</module><module>mpm_winnt</module>
-</modulelist>
+<modulelist><module>beos</module><module>leader</module>
+<module>mpm_winnt</module><module>mpmt_os2</module>
+<module>perchild</module><module>prefork</module>
+<module>threadpool</module><module>worker</module></modulelist>
<usage>
<p>The <directive>PidFile</directive> directive sets the file to
which the server records the process id of the daemon. If the
- filename does not begin with a slash (/) then it is assumed to be
- relative to the <directive module="core">ServerRoot</directive>.</p>
+ filename is not absolute then it is assumed to be relative to the
+ <directive module="core">ServerRoot</directive>.</p>
<example><title>Example</title>
PidFile /var/run/apache.pid
</example>
<p>It is often useful to be able to send the server a signal,
- so that it closes and then reopens its <directive
- module="core">ErrorLog</directive> and TransferLog, and
+ so that it closes and then re-opens its <directive
+ module="core">ErrorLog</directive> and <directive
+ module="mod_log_config">TransferLog</directive>, and
re-reads its configuration files. This is done by sending a
SIGHUP (kill -1) signal to the process id listed in the
- PidFile.</p>
+ <directive>PidFile</directive>.</p>
<p>The PidFile is subject to the same warnings about log file
placement and <a
href="../misc/security_tips.html#serverroot">security</a>.</p>
+
+ <note><title>Note</title>
+ As of Apache 2 it is recommended to use only the <a
+ href="../programs/apachectl.html">apachectl</a> script for
+ (re-)starting or stopping the server.
+ </note>
</usage>
</directivesynopsis>
listens to</description>
<syntax>Listen [<var>IP-address</var>:]<var>portnumber</var></syntax>
<contextlist><context>server config</context></contextlist>
-<modulelist><module>worker</module><module>perchild</module>
-<module>prefork</module><module>mpm_winnt</module>
+<modulelist><module>beos</module><module>leader</module>
+<module>mpm_netware</module><module>mpm_winnt</module>
+<module>mpmt_os2</module><module>perchild</module>
+<module>prefork</module><module>threadpool</module><module>worker</module>
</modulelist>
+<compatibility>Required directive since Apache 2.0</compatibility>
<usage>
<p>The <directive>Listen</directive> directive instructs Apache to
listen to only specific IP addresses or ports; by default it
- responds to requests on all IP interfaces. The Listen directive is
- now a required directive. If it is not in the config file, the
+ responds to requests on all IP interfaces. <directive>Listen</directive>
+ is now a required directive. If it is not in the config file, the
server will fail to start. This is a change from previous versions
of Apache.</p>
- <p>The Listen directive tells the server to accept incoming
- requests on the specified port or address-and-port combination.
- If only a port number is specified, the server listens to the
- given port on all interfaces. If an IP address is given as well
+ <p>The <directive>Listen</directive> directive tells the server to
+ accept incoming requests on the specified port or address-and-port
+ combination. If only a port number is specified, the server listens to
+ the given port on all interfaces. If an IP address is given as well
as a port, the server will listen on the given port and
interface.</p>
- <p>Multiple Listen directives may be used to specify a number
- of addresses and ports to listen to. The server will respond to
- requests from any of the listed addresses and ports.</p>
+ <p>Multiple <directive>Listen</directive> directives may be used to
+ specify a number of addresses and ports to listen to. The server will
+ respond to requests from any of the listed addresses and ports.</p>
<p>For example, to make the server accept connections on both
port 80 and port 8000, use:</p>
Listen [fe80::a00:20ff:fea7:ccea]:80
</example>
</usage>
-
<seealso><a href="../dns-caveats.html">DNS Issues</a></seealso>
-<seealso><a href="../bind.html">Setting
- which addresses and ports Apache uses</a></seealso>
+<seealso><a href="../bind.html">Setting which addresses and ports Apache
+uses</a></seealso>
</directivesynopsis>
<directivesynopsis>
<syntax>ListenBacklog <var>backlog</var></syntax>
<default>ListenBacklog 511</default>
<contextlist><context>server config</context></contextlist>
-<modulelist><module>worker</module><module>perchild</module>
-<module>prefork</module><module>mpm_winnt</module>
-</modulelist>
+<modulelist><module>beos</module><module>leader</module>
+<module>mpm_netware</module><module>mpm_winnt</module>
+<module>mpmt_os2</module><module>perchild</module><module>prefork</module>
+<module>threadpool</module><module>worker</module></modulelist>
<usage>
<p>The maximum length of the queue of pending connections.
<syntax>LockFile <var>filename</var></syntax>
<default>LockFile logs/accept.lock</default>
<contextlist><context>server config</context></contextlist>
-<modulelist><module>worker</module><module>perchild</module>
-<module>prefork</module></modulelist>
+<modulelist><module>leader</module><module>perchild</module>
+<module>prefork</module><module>threadpool</module><module>worker</module>
+</modulelist>
<usage>
<p>The <directive>LockFile</directive> directive sets the path to
- the lockfile used when Apache is compiled with either
- USE_FCNTL_SERIALIZED_ACCEPT or USE_FLOCK_SERIALIZED_ACCEPT. This
- directive should normally be left at its default value. The main
- reason for changing it is if the <code>logs</code> directory is
- NFS mounted, since <strong>the lockfile must be stored on a local
- disk</strong>. The PID of the main server process is
- automatically appended to the filename.</p>
+ the lockfile used when Apache is used with an <directive
+ module="mpm_common">AcceptMutex</directive> value of either
+ <code>fcntl</code> or <code>flock</code>. This directive should
+ normally be left at its default value. The main reason for changing
+ it is if the <code>logs</code> directory is NFS mounted, since
+ <strong>the lockfile must be stored on a local disk</strong>. The PID
+ of the main server process is automatically appended to the
+ filename.</p>
<note type="warning"><title>Security:</title>
- <p>It is best to avoid putting this file in a world writable directory
- such as <code>/var/tmp</code> because someone could create a denial of
- service attack and prevent the server from starting by creating
- a lockfile with the same name as the one the server will try to
- create.</p>
+ <p>It is best to <em>avoid</em> putting this file in a world writable
+ directory such as <code>/var/tmp</code> because someone could create
+ a denial of service attack and prevent the server from starting by
+ creating a lockfile with the same name as the one the server will try
+ to create.</p>
</note>
</usage>
+<seealso><directive module="mpm_common">AcceptMutex</directive></seealso>
</directivesynopsis>
<directivesynopsis>
<description>Maximum number of child processes that will be created
to serve requests</description>
<syntax>MaxClients <var>number</var></syntax>
+<default>See usage for details</default>
<contextlist><context>server config</context></contextlist>
-<modulelist><module>worker</module><module>prefork</module>
+<modulelist><module>beos</module><module>leader</module>
+<module>prefork</module><module>threadpool</module><module>worker</module>
</modulelist>
<usage>
directive. Once a child process is freed at the end of a different
request, the connection will then be serviced.</p>
- <p>For non-threaded servers (i.e., <module>prefork</module>),
+ <p>For non-threaded servers (<em>i.e.</em>, <module>prefork</module>),
<directive>MaxClients</directive> translates into the maximum
number of child processes that will be launched to serve requests.
The default value is 256; to increase it, you must also raise
<directive module="mpm_common">ServerLimit</directive>.</p>
- <p>For threaded servers (i.e., <module>worker</module>),
- <directive>MaxClients</directive> restricts the total
- number of threads that will be available to serve clients.
- The default value is 16 multiplied by the value of
- <directive module="mpm_common">ThreadsPerChild</directive>.
- To increase <directive>MaxClients</directive> to a value
- that requires more than 16 processes, you must also
- raise <directive module="mpm_common">ServerLimit</directive>.</p>
+ <p>For threaded and hybrid servers (<em>e.g.</em> <module>beos</module>
+ or <module>worker</module>) <directive>MaxClients</directive> restricts
+ the total number of threads that will be available to serve clients.
+ The default value for <module>beos</module> is <code>50</code>. For
+ hybrid MPMs the default value is <code>16</code> (<directive
+ module="mpm_common">ServerLimit</directive>) multiplied by the value of
+ <code>25</code> (<directive module="mpm_common"
+ >ThreadsPerChild</directive>). Therefore, to increase <directive
+ >MaxClients</directive> to a value that requires more than 16 processes,
+ you must also raise <directive module="mpm_common"
+ >ServerLimit</directive>.</p>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>MaxMemFree</name>
<description>Maximum amount of memory that the main allocator is allowed
-to hold without calling free()</description>
-<syntax>MaxMemFree <var>number</var></syntax>
+to hold without calling <code>free()</code></description>
+<syntax>MaxMemFree <var>KBytes</var></syntax>
+<default>MaxMemFree 0</default>
<contextlist><context>server config</context></contextlist>
-<modulelist><module>worker</module><module>prefork</module>
-<module>mpm_netware</module>
-</modulelist>
+<modulelist><module>beos</module><module>leader</module>
+<module>mpm_netware</module><module>prefork</module>
+<module>threadpool</module><module>worker</module></modulelist>
<usage>
<p>The <directive>MaxMemFree</directive> directive sets the
maximum number of free Kbytes that the main allocator is allowed
- to hold without calling free(). When not set, or when set to
- zero, the threshold will be set to unlimited.</p>
+ to hold without calling <code>free()</code>. When not set, or when set
+ to zero, the threshold will be set to unlimited.</p>
</usage>
</directivesynopsis>
<syntax>MaxRequestsPerChild <var>number</var></syntax>
<default>MaxRequestsPerChild 10000</default>
<contextlist><context>server config</context></contextlist>
-<modulelist><module>worker</module><module>perchild</module>
-<module>prefork</module><module>mpm_winnt</module>
-</modulelist>
+<modulelist><module>leader</module><module>mpm_netware</module>
+<module>mpm_winnt</module><module>mpmt_os2</module>
+<module>perchild</module><module>prefork</module>
+<module>threadpool</module><module>worker</module></modulelist>
<usage>
<p>The <directive>MaxRequestsPerChild</directive> directive sets
server process will handle. After
<directive>MaxRequestsPerChild</directive> requests, the child
process will die. If <directive>MaxRequestsPerChild</directive> is
- 0, then the process will never expire.</p>
+ <code>0</code>, then the process will never expire.</p>
+
+ <note><title>Different default values:</title>
+ <p>The default value for <module>mpm_netware</module> and
+ <module>mpm_winnt</module> is <code>0</code>.</p>
+ </note>
<p>Setting <directive>MaxRequestsPerChild</directive> to a
non-zero limit has two beneficial effects:</p>
</ul>
<note><title>Note:</title>
- <p>For <em>KeepAlive</em> requests, only the first request is counted
- towards this limit. In effect, it changes the behavior to limit the
- number of <em>connections</em> per child.</p>
+ <p>For <directive module="core">KeepAlive</directive> requests, only
+ the first request is counted towards this limit. In effect, it
+ changes the behavior to limit the number of <em>connections</em> per
+ child.</p>
</note>
</usage>
</directivesynopsis>
<name>MaxSpareThreads</name>
<description>Maximum number of idle threads</description>
<syntax>MaxSpareThreads <var>number</var></syntax>
+<default>See usage for details</default>
<contextlist><context>server config</context></contextlist>
-<modulelist><module>mpm_netware</module>
-<module>perchild</module><module>worker</module>
+<modulelist><module>beos</module><module>leader</module>
+<module>mpm_netware</module><module>mpmt_os2</module>
+<module>perchild</module><module>threadpool</module><module>worker</module>
</modulelist>
<usage>
directive differently.</p>
<p>For <module>perchild</module> the default is
- <code>MaxSpareThreads 10</code>. This MPM monitors the number of
+ <code>MaxSpareThreads 10</code>. This MPM monitors the number of
idle threads on a per-child basis. If there are too many idle
threads in that child, the server will begin to kill threads
within that child.</p>
- <p>For <module>worker</module> the default is
- <code>MaxSpareThreads 500</code>. This MPM deals with idle threads
- on a server-wide basis. If there are too many idle threads in the
- server then child processes are killed until the number of idle
- threads is less than this number.</p>
+ <p>For <module>worker</module>, <module>leader</module> and <module
+ >threadpool</module> the default is <code>MaxSpareThreads 250</code>.
+ These MPMs deal with idle threads on a server-wide basis. If there
+ are too many idle threads in the server then child processes are
+ killed until the number of idle threads is less than this number.</p>
<p>For <module>mpm_netware</module> the default is
- <code>MaxSpareThreads 100</code>. Since this MPM runs a
+ <code>MaxSpareThreads 100</code>. Since this MPM runs a
single-process, the spare thread count is also server-wide.</p>
+ <p><module>beos</module> and <module>mpmt_os2</module> work
+ similar to <module>mpm_netware</module>. The default for
+ <module>beos</module> is <code>MaxSpareThreads 50</code>. For
+ <module>mpmt_os2</module> the default value is <code>10</code>.</p>
+
+ <note><title>Restrictions</title>
+ <p>The range of the <directive>MaxSpareThreads</directive> value
+ is restricted. Apache will correct the given value automatically
+ according to the following rules:</p>
+ <ul>
+ <li><module>perchild</module> requires <directive
+ >MaxSpareThreads</directive> to be less or equal than <directive
+ module="mpm_common">ThreadLimit</directive>.</li>
+
+ <li><module>mpm_netware</module> wants the value to be greater than
+ <directive module="mpm_common">MinSpareThreads</directive>.</li>
+
+ <li>For <module>leader</module>, <module>threadpool</module> and
+ <module>worker</module> the value must be greater or equal than
+ the sum of <directive module="mpm_common">MinSpareThreads</directive>
+ and <directive module="mpm_common">ThreadsPerChild</directive>.</li>
+ </ul>
+ </note>
</usage>
<seealso><directive module="mpm_common">MinSpareThreads</directive></seealso>
<seealso><directive module="mpm_common">StartServers</directive></seealso>
</directivesynopsis>
-<directivesynopsis>
-<name>MaxThreadsPerChild</name>
-<description>Maximum number of threads per child process</description>
-<syntax>MaxThreadsPerChild <var>number</var></syntax>
-<default>MaxThreadsPerChild 64</default>
-<contextlist><context>server config</context></contextlist>
-<modulelist><module>worker</module><module>perchild</module>
-</modulelist>
-
-<usage>
- <p>Maximum number of threads per child. For MPMs with a
- variable number of threads per child, this directive sets the
- maximum number of threads that will be created in each child
- process. To increase this value beyond its default, it is
- necessary to change the value of the compile-time define
- <code>HARD_THREAD_LIMIT</code> and recompile the server.</p>
-</usage>
-</directivesynopsis>
-
<directivesynopsis>
<name>MinSpareThreads</name>
<description>Minimum number of idle threads available to handle request
spikes</description>
<syntax>MinSpareThreads <var>number</var></syntax>
+<default>See usage for details</default>
<contextlist><context>server config</context></contextlist>
-<modulelist><module>mpm_netware</module>
-<module>perchild</module><module>worker</module>
+<modulelist><module>beos</module><module>leader</module>
+<module>mpm_netware</module><module>mpmt_os2</module>
+<module>perchild</module><module>threadpool</module><module>worker</module>
</modulelist>
<usage>
<code>MinSpareThreads 5</code> and monitors the number of idle
threads on a per-child basis. If there aren't enough idle threads
in that child, the server will begin to create new threads within
- that child.</p>
-
- <p><module>worker</module> uses a default of <code>MinSpareThreads
- 250</code> and deals with idle threads on a server-wide basis. If
+ that child. Thus, if you set <directive module="perchild"
+ >NumServers</directive> to <code>10</code> and a <directive
+ >MinSpareThreads</directive> value of <code>5</code>, you'll have
+ at least 50 idle threads on your system.</p>
+
+ <p><module>worker</module>, <module>leader</module> and
+ <module>threadpool</module> use a default of <code>MinSpareThreads
+ 75</code> and deal with idle threads on a server-wide basis. If
there aren't enough idle threads in the server then child
processes are created until the number of idle threads is greater
than number.</p>
<code>MinSpareThreads 10</code> and, since it is a single-process
MPM, tracks this on a server-wide bases.</p>
+ <p><module>beos</module> and <module>mpmt_os2</module> work
+ similar to <module>mpm_netware</module>. The default for
+ <module>beos</module> is <code>MinSpareThreads 1</code>. For
+ <module>mpmt_os2</module> the default value is <code>5</code>.</p>
</usage>
<seealso><directive module="mpm_common">MaxSpareThreads</directive></seealso>
<seealso><directive module="mpm_common">StartServers</directive></seealso>
</directivesynopsis>
-<directivesynopsis>
-<name>NumServers</name>
-<description>Total number of children alive at the same time</description>
-<syntax>NumServers <var>number</var></syntax>
-<default>NumServers 2</default>
-<contextlist><context>server config</context></contextlist>
-<modulelist><module>perchild</module></modulelist>
-
-<usage>
- <p>Number of children alive at the same time. MPMs that use
- this directive do not dynamically create new child processes so
- this number should be large enough to handle the requests for
- the entire site.</p>
-</usage>
-</directivesynopsis>
-
<directivesynopsis>
<name>ScoreBoardFile</name>
<description>Location of the file used to store coordination data for
<syntax>ScoreBoardFile <var>file-path</var></syntax>
<default>ScoreBoardFile logs/apache_status</default>
<contextlist><context>server config</context></contextlist>
-<modulelist><module>worker</module><module>perchild</module>
-<module>prefork</module></modulelist>
+<modulelist><module>beos</module><module>leader</module>
+<module>mpm_winnt</module><module>perchild</module><module>prefork</module>
+<module>threadpool</module><module>worker</module></modulelist>
<usage>
<p>Apache uses a scoreboard to communicate between its parent
careful that you heed the same warnings about log file placement
and <a href="../misc/security_tips.html">security</a>.</p>
</usage>
-<seealso><a
- href="../stopping.html">Stopping and Restarting Apache</a></seealso>
+<seealso><a href="../stopping.html">Stopping and Restarting
+Apache</a></seealso>
</directivesynopsis>
<directivesynopsis>
<name>SendBufferSize</name>
<description>TCP buffer size</description>
<syntax>SendBufferSize <var>bytes</var></syntax>
+<default>SendBufferSize 0</default>
<contextlist><context>server config</context></contextlist>
-<modulelist><module>worker</module><module>perchild</module>
-<module>prefork</module><module>mpm_winnt</module>
-</modulelist>
+<modulelist><module>beos</module><module>leader</module>
+<module>mpm_netware</module><module>mpm_winnt</module>
+<module>mpmt_os2</module><module>perchild</module><module>prefork</module>
+<module>threadpool</module><module>worker</module></modulelist>
<usage>
<p>The server will set the TCP buffer size to the number of bytes
specified. Very useful to increase past standard OS defaults on
high speed high latency (<em>i.e.</em>, 100ms or so, such as
transcontinental fast pipes).</p>
+
+ <p>If set to the value of <code>0</code>, the server will use the
+ OS deault.</p>
</usage>
</directivesynopsis>
<name>ServerLimit</name>
<description>Upper limit on configurable number of processes</description>
<syntax>ServerLimit <var>number</var></syntax>
-<default>ServerLimit 256 (prefork), ServerLimit 16 (worker)</default>
+<default>See usage for details</default>
<contextlist><context>server config</context></contextlist>
-<modulelist><module>worker</module><module>prefork</module>
+<modulelist><module>leader</module><module>perchild</module>
+<module>prefork</module><module>threadpool</module><module>worker</module>
</modulelist>
<usage>
<p>With the <module>prefork</module> MPM, use this directive only
if you need to set <directive
- module="mpm_common">MaxClients</directive> higher than 256.
+ module="mpm_common">MaxClients</directive> higher than 256 (default).
Do not set the value of this directive any higher than what you
might want to set <directive
module="mpm_common">MaxClients</directive> to.</p>
- <p>With the <module>worker</module> MPM, use this directive only
+ <p>With <module>worker</module>, <module>leader</module> and
+ <module>threadpool</module> use this directive only
if your <directive module="mpm_common">MaxClients</directive> and
<directive module="mpm_common">ThreadsPerChild</directive>
- settings require more than 16 server processes. Do not set the
- value of this directive any higher than the number of server
+ settings require more than 16 server processes (default). Do not set
+ the value of this directive any higher than the number of server
processes required by what you may want for <directive
module="mpm_common">MaxClients </directive> and <directive
module="mpm_common">ThreadsPerChild</directive>.</p>
+
+ <p>With the <module>perchild</module> MPM, use this directive only
+ if you need to set <directive
+ module="perchild">NumServers</directive> higher than 8 (default).</p>
+
+ <note><title>Note</title>
+ <p>There is a hard limit of <code>ServerLimit 20000</code> compiled
+ into the server. This is intended to avoid nasty effects caused by
+ typos.</p>
+ </note>
</usage>
+<seealso><a href="../stopping.html">Stopping and Restarting Apache</a></seealso>
</directivesynopsis>
<directivesynopsis>
<name>StartServers</name>
<description>Number of child server processes created at startup</description>
<syntax>StartServers <var>number</var></syntax>
-<default>StartServers 5</default>
+<default>See usage for details</default>
<contextlist><context>server config</context></contextlist>
-<modulelist><module>worker</module></modulelist>
+<modulelist><module>leader</module><module>mpmt_os2</module>
+<module>prefork</module><module>threadpool</module><module>worker</module>
+</modulelist>
<usage>
<p>The <directive>StartServers</directive> directive sets the
number of child server processes created on startup. As the number
of processes is dynamically controlled depending on the load,
there is usually little reason to adjust this parameter.</p>
+
+ <p>The default value differs from MPM to MPM. For
+ <module>leader</module>, <module>threadpool</module> and
+ <module>worker</module> the default is <code>StartServers 3</code>.
+ For <module>prefork</module> defaults to <code>5</code> and for
+ <module>mpmt_os2</module> to <code>2</code>.</p>
</usage>
-<seealso><directive module="mpm_common">MinSpareThreads</directive></seealso>
-<seealso><directive module="mpm_common">MaxSpareThreads</directive></seealso>
</directivesynopsis>
<directivesynopsis>
<name>StartThreads</name>
-<description>Nubmer of threads created on startup</description>
+<description>Number of threads created on startup</description>
<syntax>StartThreads <var>number</var></syntax>
+<default>See usage for details</default>
<contextlist><context>server config</context></contextlist>
-<modulelist><module>mpm_netware</module><module>perchild</module></modulelist>
+<modulelist><module>beos</module><module>mpm_netware</module>
+<module>perchild</module></modulelist>
<usage>
<p>Number of threads created on startup. As the
process, this is the total number of threads created at startup to
serve requests.</p>
+ <p>For <module>beos</module> the default is <code>StartThreads
+ 10</code>. It also reflects the total number of threads created
+ at startup to serve requests.</p>
</usage>
</directivesynopsis>
<description>Sets the upper limit on the configurable number of threads
per child process</description>
<syntax>ThreadLimit <var>number</var></syntax>
+<default>See usage for details</default>
<contextlist><context>server config</context></contextlist>
-<modulelist><module>mpm_winnt</module><module>worker</module></modulelist>
+<modulelist><module>leader</module><module>mpm_winnt</module>
+<module>perchild</module><module>threadpool</module><module>worker</module>
+</modulelist>
+<compatibility>Available for <module>mpm_winnt</module> in Apache 2.0.41
+and later</compatibility>
<usage>
<p>This directive sets the maximum configured value for <directive
current run of Apache.</p>
<p>The default value for <directive>ThreadLimit</directive> is
- 64 when used with <module>worker</module> and 1920 when used
- with <module>mpm_winnt</module>.</p>
-
+ <code>1920</code> when used with <module>mpm_winnt</module> and
+ <code>64</code> when used with the others.</p>
+
+ <note><title>Note</title>
+ <p>There is a hard limit of <code>ThreadLimit 20000</code> (or
+ <code>ThreadLimit 15000</code> with <module>mpm_winnt</module>)
+ compiled into the server. This is intended to avoid nasty effects
+ caused by typos.</p>
+ </note>
</usage>
</directivesynopsis>
<name>ThreadsPerChild</name>
<description>Number of threads created by each child process</description>
<syntax>ThreadsPerChild <var>number</var></syntax>
+<default>See usage for details</default>
<contextlist><context>server config</context></contextlist>
-<modulelist><module>worker</module><module>mpm_winnt</module>
-</modulelist>
+<modulelist><module>leader</module><module>mpm_winnt</module>
+<module>threadpool</module><module>worker</module></modulelist>
<usage>
<p>This directive sets the number of threads created by each
child process. The child creates these threads at startup and
- never creates more. If using an MPM like mpmt_winnt, where
- there is only one child process, this number should be high
+ never creates more. If using an MPM like <module>mpm_winnt</module>,
+ where there is only one child process, this number should be high
enough to handle the entire load of the server. If using an MPM
- like worker, where there are multiple child processes, the
- total number of threads should be high enough to handle the
- common load on the server.</p>
-
- <p>The default value for this directive is 25 when used with
- <module>worker</module> and 64 when used with
- <module>mpm_winnt</module>.</p>
+ like <module>worker</module>, where there are multiple child processes,
+ the <em>total</em> number of threads should be high enough to handle
+ the common load on the server.</p>
+ <p>The default value for <directive>ThreadsPerChild</directive> is
+ <code>64</code> when used with <module>mpm_winnt</module> and
+ <code>25</code> when used with the others.</p>
</usage>
</directivesynopsis>
requests</description>
<syntax>User <var>unix-userid</var></syntax>
<default>User #-1</default>
-<contextlist><context>server config</context><context>virtual host</context>
-</contextlist>
-<modulelist><module>worker</module><module>perchild</module>
-<module>prefork</module></modulelist>
+<contextlist><context>server config</context></contextlist>
+<modulelist><module>leader</module><module>perchild</module>
+<module>prefork</module><module>threadpool</module><module>worker</module>
+</modulelist>
+<compatibility>Only valid in global server config since Apache
+2.0</compatibility>
<usage>
- <p>The <directive>User</directive> directive sets the userid as
+ <p>The <directive>User</directive> directive sets the user ID as
which the server will answer requests. In order to use this
- directive, the standalone server must be run initially as
- root. <var>Unix-userid</var> is one of:</p>
+ directive, the server must be run initially as <code>root</code>.
+ If you start the server as a non-root user, it will fail to change
+ to the lesser privileged user, and will instead continue to run as
+ that original user. If you do start the server as <code>root</code>,
+ then it is normal for the parent process to remain running as root.
+ <var>Unix-userid</var> is one of:</p>
<dl>
<dt>A username</dt>
-
<dd>Refers to the given user by name.</dd>
<dt># followed by a user number.</dt>
-
- <dd>Refers to a user by their number.</dd>
+ <dd>Refers to a user by its number.</dd>
</dl>
<p>The user should have no privileges that result in it being
able to access files that are not intended to be visible to the
outside world, and similarly, the user should not be able to
- execute code that is not meant for httpd requests. It is
+ execute code that is not meant for HTTP requests. It is
recommended that you set up a new user and group specifically for
running the server. Some admins use user <code>nobody</code>, but
this is not always desirable, since the <code>nobody</code> user
can have other uses on the system.</p>
- <p>Notes: If you start the server as a non-root user, it will
- fail to change to the lesser privileged user, and will instead
- continue to run as that original user. If you do start the
- server as root, then it is normal for the parent process to
- remain running as root.</p>
+ <note type="warning"><title>Security</title>
+ <p>Don't set <directive>User</directive> (or <directive
+ module="mpm_common">Group</directive>) to <code>root</code> unless
+ you know exactly what you are doing, and what the dangers are.</p>
+ </note>
+
+ <p>With the <module>perchild</module> MPM, which is intended to
+ server virtual hosts run under different user IDs, the
+ <directive>User</directive> directive defines the user ID for the
+ main server and the fallback for <directive type="section"
+ module="core">VirtualHost</directive> sections without an
+ <directive module="perchild">AssignUserID</directive> directive.</p>
<p>Special note: Use of this directive in <directive module="core"
type="section">VirtualHost</directive> is no longer supported. To
- configure your server for <a href="mod_suexec.html">suexec</a> use
+ configure your server for <a href="../suexec.html">suexec</a> use
<directive module="mod_suexec">SuexecUserGroup</directive>.</p>
-<note><title>Security</title> <p>Don't set <directive>User</directive>
-(or <directive module="mpm_common">Group</directive>) to
-<code>root</code> unless you know exactly what you are doing, and what
-the dangers are.</p></note>
+ <note><title>Note</title>
+ <p>Although the <directive>User</directive> directive is present
+ in the <module>beos</module> and <module>mpmt_os2</module> MPMs,
+ it is actually a no-op there and only exists for compatibility
+ reasons.</p>
+ </note>
</usage>
</directivesynopsis>
<modulesynopsis>
<name>perchild</name>
-<description>Multi-Processing Module allowing for daemon processes
- serving requests to be assigned a variety of different
- userids</description>
+<description>Multi-Processing Module allowing for daemon processes serving
+requests to be assigned a variety of different userids</description>
<status>MPM</status>
<sourcefile>perchild.c</sourcefile>
<identifier>mpm_perchild_module</identifier>
<summary>
-<note type="warning">
-This MPM does not currently work on most platforms. Work is ongoing to
-make it functional.
-</note>
+ <note type="warning">
+ This MPM does not currently work on most platforms. Work is ongoing
+ to make it functional.
+ </note>
<p>This Multi-Processing Module (MPM) implements a hybrid
multi-process, multi-threaded web server. A fixed number of
processes create threads to handle requests. Fluctuations in
load are handled by increasing or decreasing the number of
threads in each process.</p>
+</summary>
+<seealso><a href="../bind.html">Setting which addresses and ports Apache
+uses</a></seealso>
+<section id="how-it-works"><title>How it works</title>
<p>A single control process launches the number of child processes
- indicated by the <directive
- module="mpm_common">NumServers</directive> directive at server
- startup. Each child process creates threads as specified in the
- <directive module="mpm_common">StartThreads</directive> directive.
+ indicated by the <directive module="perchild">NumServers</directive>
+ directive at server startup. Each child process creates threads as
+ specified in the <directive module="mpm_common">StartThreads</directive> directive.
The individual threads then
listen for connections and serve them when they arrive.</p>
The maximum number of clients that may be served simultaneously
is determined by multiplying the number of server processes
that will be created (<directive
- module="mpm_common">NumServers</directive>) by the maximum
+ module="perchild">NumServers</directive>) by the maximum
number of threads created in each process
(<directive module="mpm_common">MaxThreadsPerChild</directive>).</p>
server recycles processes by killing old ones and launching new
ones.</p>
- <p>In addition it adds the extra ability to specify that
- specific processes should serve requests under different
- userids. These processes can then be associated with specific
- virtual hosts.</p>
- <!-- XXX: This desperately needs more explanation. -->
-</summary>
-<seealso><a href="../bind.html">Setting which addresses and
- ports Apache uses</a>
-</seealso>
+ <section id="user-ids"><title>Working with different user-IDs</title>
+ <p>The <module>perchild</module> MPM adds the extra ability to
+ specify that particular processes should serve requests under
+ different user-IDs. These user-IDs can then be associated with
+ specific virtual hosts. You have to use one <directive
+ module="perchild">ChildPerUserID</directive> directive for
+ every user/group combination you want to be run. Then you can tie
+ particular virtual hosts to that user and group IDs.</p>
+
+ <p>The following example runs 7 child processes. Two of them are run
+ under <code>user1</code>/<code>group1</code>. The next four are run
+ under <code>user2</code>/<code>group2</code> and the remaining
+ process uses the <directive module="mpm_common"
+ >User</directive> and <directive module="mpm_common">Group</directive>
+ of the main server:</p>
+
+ <example><title>Global config</title>
+ NumServers 7<br />
+ ChildPerUserID user1 group1 2<br />
+ ChildPerUserID user2 group2 4
+ </example>
-<directivesynopsis location="mpm_common">
-<name>CoreDumpDirectory</name>
+ <p>Using unbalanced numbers of processes as above is useful, if the
+ particular virtual hosts produce different load. The assignment to
+ the virtual hosts is easily done as in the example below. In
+ conclusion with the example above the following assumes, that
+ <code>server2</code> has to serve about twice of the hits of
+ <code>server1</code>.</p>
+
+ <example><title>Example</title>
+ NameVirtualHost *<br />
+ <br />
+ <VirtualHost *><br />
+ <indent>
+ ServerName fallbackhost<br />
+ # no assignment; use fallback<br />
+ </indent>
+ </VirtualHost><br />
+ <br />
+ <VirtualHost *><br />
+ <indent>
+ ServerName server1<br />
+ AssignUserID user1 group1<br />
+ </indent>
+ </VirtualHost><br />
+ <br />
+ <VirtualHost *><br />
+ <indent>
+ ServerName server2<br />
+ AssignUserID user2 group2<br />
+ </indent>
+ </VirtualHost>
+ </example>
+ </section>
+</section>
+
+<directivesynopsis location="mpm_common"><name>AcceptMutex</name>
</directivesynopsis>
-<directivesynopsis location="mpm_common">
-<name>Group</name>
+<directivesynopsis location="mpm_common"><name>BS2000Account</name>
</directivesynopsis>
-<directivesynopsis location="mpm_common">
-<name>PidFile</name>
+<directivesynopsis location="mpm_common"><name>CoreDumpDirectory</name>
</directivesynopsis>
-<directivesynopsis location="mpm_common">
-<name>Listen</name>
+<directivesynopsis location="mpm_common"><name>Group</name>
</directivesynopsis>
-<directivesynopsis location="mpm_common">
-<name>ListenBacklog</name>
+<directivesynopsis location="mpm_common"><name>PidFile</name>
</directivesynopsis>
-<directivesynopsis location="mpm_common">
-<name>LockFile</name>
+<directivesynopsis location="mpm_common"><name>Listen</name>
</directivesynopsis>
-<directivesynopsis location="mpm_common">
-<name>MaxRequestsPerChild</name>
+<directivesynopsis location="mpm_common"><name>ListenBacklog</name>
</directivesynopsis>
-<directivesynopsis location="mpm_common">
-<name>MaxSpareThreads</name>
+<directivesynopsis location="mpm_common"><name>LockFile</name>
</directivesynopsis>
-<directivesynopsis location="mpm_common">
-<name>MaxThreadsPerChild</name>
+<directivesynopsis location="mpm_common"><name>MaxRequestsPerChild</name>
</directivesynopsis>
-<directivesynopsis location="mpm_common">
-<name>MinSpareThreads</name>
+<directivesynopsis location="mpm_common"><name>MaxSpareThreads</name>
</directivesynopsis>
-<directivesynopsis location="mpm_common">
-<name>NumServers</name>
+<directivesynopsis location="mpm_common"><name>MinSpareThreads</name>
</directivesynopsis>
-<directivesynopsis location="mpm_common">
-<name>ScoreBoardFile</name>
+<directivesynopsis location="mpm_common"><name>ScoreBoardFile</name>
</directivesynopsis>
-<directivesynopsis location="mpm_common">
-<name>SendBufferSize</name>
+<directivesynopsis location="mpm_common"><name>SendBufferSize</name>
</directivesynopsis>
-<directivesynopsis location="mpm_common">
-<name>StartThreads</name>
+<directivesynopsis location="mpm_common"><name>ServerLimit</name>
</directivesynopsis>
-<directivesynopsis location="mpm_common">
-<name>User</name>
+<directivesynopsis location="mpm_common"><name>StartThreads</name>
+</directivesynopsis>
+<directivesynopsis location="mpm_common"><name>ThreadLimit</name>
+</directivesynopsis>
+<directivesynopsis location="mpm_common"><name>User</name>
</directivesynopsis>
<directivesynopsis>
-<name>AssignUserId</name>
-<syntax>AssignUserID <var>user_id</var> <var>group_id</var></syntax>
+<name>AssignUserID</name>
+<description>Tie a virtual host to a user and group ID</description>
+<syntax>AssignUserID <var>user-id</var> <var>group-id</var></syntax>
<contextlist><context>virtual host</context></contextlist>
<usage>
- <p>Tie a virtual host to a specific child process. Requests addressed to
-the virtual host where this directive appears will be served by the process
-running with the specified user and group id.</p>
+ <p>Tie a virtual host to a specific user/group combination. Requests
+ addressed to the virtual host where this directive appears will be
+ served by a process running with the specified user and group ID.</p>
+
+ <p>The user and group ID has to be assigned to a number of children
+ in the global server config using the <directive module="perchild"
+ >ChildPerUserID</directive> directive. See the section above for a
+ <a href="#user-ids">configuration example</a>.</p>
</usage>
</directivesynopsis>
<directivesynopsis>
-<name>ChildPerUserId</name>
-<syntax>ChildPerUserID <var>user_id</var>
-<var>group_id</var> <var>num_children</var></syntax>
+<name>ChildPerUserID</name>
+<description>Specify user ID and group ID for a number of child
+processes</description>
+<syntax>ChildPerUserID <var>user-id</var> <var>group-id</var>
+<var>num-children</var></syntax>
<contextlist><context>server config</context></contextlist>
<usage>
-<p>Specify a user id and group id for a number of child processes. The third
-argument, num_children, is the number of child processes to start with the
-specified user and group. It does <strong>not</strong> represent a specific
-child number. If the total number of child processes, found by totaling all of
-the third arguments to all ChildPerUserId directives in the config file, is
-less than <directive module="mpm_common">NumServers</directive>, then all
-remaining children will inherit the <directive
-module="mpm_common">User</directive> and <directive
-module="mpm_common">Group</directive> settings from the main server </p>
+ <p>Specify a user ID and group ID for a number of child processes.
+ The third argument, <var>num-children</var>, is the number of child
+ processes to start with the specified user and group. It does
+ <em>not</em> represent a specific child number. In order to use this
+ directive, the server must be run initially as <code>root</code>.
+ If you start the server as a non-root user, it will fail to change
+ to the lesser privileged user.</p>
+
+ <p>If the total number of child processes, found by totaling all of the
+ third arguments to all <directive>ChildPerUserID</directive> directives
+ in the config file, is less than <directive module="perchild"
+ >NumServers</directive>, then all remaining children will inherit the
+ <directive module="mpm_common">User</directive> and <directive
+ module="mpm_common">Group</directive> settings from the main server.
+ See the section above for a <a href="#user-ids">configuration
+ example</a>.</p>
+
+ <note type="warning"><title>Security</title>
+ <p>Don't set <var>user-id</var> (or <var>group-id</var>) to
+ <code>root</code> unless you know exactly what you are doing, and
+ what the dangers are.</p>
+ </note>
</usage>
</directivesynopsis>
-</modulesynopsis>
+<directivesynopsis>
+<name>MaxThreadsPerChild</name>
+<description>Maximum number of threads per child process</description>
+<syntax>MaxThreadsPerChild <var>number</var></syntax>
+<default>MaxThreadsPerChild 64</default>
+<contextlist><context>server config</context></contextlist>
+
+<usage>
+ <p>This directive sets the maximum number of threads that will be
+ created in each child process. To increase this value beyond its
+ default, it is necessary to change the value of the <directive
+ module="mpm_common">ThreadLimit</directive> directive and stop and
+ re-start the server.</p>
+</usage>
+</directivesynopsis>
+<directivesynopsis>
+<name>NumServers</name>
+<description>Total number of children alive at the same time</description>
+<syntax>NumServers <var>number</var></syntax>
+<default>NumServers 2</default>
+<contextlist><context>server config</context></contextlist>
+
+<usage>
+ <p>The <directive>NumServers</directive> directive determines the number
+ of children alive at the same time. This number should be large enough to
+ handle the requests for the entire site. To increase this value beyond the
+ value of <code>8</code>, it is necessary to change the value of the
+ <directive module="mpm_common">ServerLimit</directive> directive and stop
+ and re-start the server. See the section above for a <a href="#user-ids"
+ >configuration example</a>.</p>
+</usage>
+</directivesynopsis>
+
+</modulesynopsis>
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