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<!DOCTYPE modulesynopsis SYSTEM "/style/modulesynopsis.dtd">

<?xml-stylesheet type="text/xsl" href="/style/manual.en.xsl"?>

<modulesynopsis metafile="mpm_common.xml.meta">

<name>mpm_common</name>

<description>A collection of directives that are implemented by

more than one multi-processing module (MPM)</description>

<status>MPM</status>

<directivesynopsis>

<name>CoreDumpDirectory</name>

<description>Directory where Apache HTTP Server attempts to

switch before dumping core</description>

<syntax>CoreDumpDirectory <var>directory</var></syntax>

<default>See usage for the default setting</default>

<contextlist><context>server config</context></contextlist>

<modulelist><module>mpm_winnt</module><module>prefork</module>

<module>worker</module></modulelist>

<usage>

<p>This controls the directory to which Apache httpd attempts to

switch before dumping core. If your operating system is configured to

create core files in the working directory of the crashing process,

<directive>CoreDumpDirectory</directive> is necessary to change working

directory from the default <directive module="core">ServerRoot</directive>

directory, which should not be writable by the user the server runs as.</p>

<p>If you want a core dump for debugging, you can use this directive to

place it in a different location. This directive has no effect if your

operating system is not configured to write core files to the working directory

of the crashing processes.</p>

<note><title>Core Dumps on Linux</title>

<p>If Apache httpd starts as root and switches to another user, the

Linux kernel <em>disables</em> core dumps even if the directory is

writable for the process. Apache httpd (2.0.46 and later) reenables core dumps

on Linux 2.4 and beyond, but only if you explicitly configure a <directive

>CoreDumpDirectory</directive>.</p>

</note>

<note><title>Specific signals</title>

<p><directive>CoreDumpDirectory</directive> processing only occurs for

a select set of fatal signals: SIGFPE, SIGILL, SIGABORT,

SIGSEGV, and SIGBUS.</p>

<p>On some operating systems, SIGQUIT also results in a core dump but

does not go through <directive>CoreDumpDirectory</directive> or

<directive>EnableExceptionHook</directive> processing, so the core

location is dictated entirely by the operating system.</p>

</note>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>EnableExceptionHook</name>

<description>Enables a hook that runs exception handlers

after a crash</description>

<syntax>EnableExceptionHook On|Off</syntax>

<default>EnableExceptionHook Off</default>

<contextlist><context>server config</context></contextlist>

<modulelist>

<module>prefork</module><module>worker</module></modulelist>

<compatibility>Available in version 2.0.49 and later</compatibility>

<usage>

<p>For safety reasons this directive is only available if the server was

configured with the <code>--enable-exception-hook</code> option. It

enables a hook that allows external modules to plug in and do something

after a child crashed.</p>

<p>There are already two modules, <code>mod_whatkilledus</code> and

<code>mod_backtrace</code> that make use of this hook. Please have a

look at Jeff Trawick's <a

href="http://www.apache.org/~trawick/exception_hook.html"

>EnableExceptionHook site</a> for more information about these.</p>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>GracefulShutdownTimeout</name>

<description>Specify a timeout after which a gracefully shutdown server

will exit.</description>

<syntax>GracefulShutDownTimeout <var>seconds</var></syntax>

<default>GracefulShutDownTimeout 0</default>

<contextlist><context>server config</context></contextlist>

<modulelist><module>prefork</module><module>worker</module>

<module>event</module></modulelist>

<compatibility>Available in version 2.2 and later</compatibility>

<usage>

<p>The <directive>GracefulShutdownTimeout</directive> specifies

how many seconds after receiving a "graceful-stop" signal, a

server should continue to run, handling the existing connections.</p>

<p>Setting this value to zero means that the server will wait

indefinitely until all remaining requests have been fully served.</p>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>PidFile</name>

<description>File where the server records the process ID

of the daemon</description>

<syntax>PidFile <var>filename</var></syntax>

<default>PidFile logs/httpd.pid</default>

<contextlist><context>server config</context></contextlist>

<modulelist><module>mpm_winnt</module><module>mpmt_os2</module>

<module>prefork</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 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 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

<directive>PidFile</directive>.</p>

<p>The <directive>PidFile</directive> 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>

<p>As of Apache HTTP Server 2, we recommended that you only use the <program>

apachectl</program> script, or the init script that your OS provides,

for (re-)starting or stopping the server.</p>

</note>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>Listen</name>

<description>IP addresses and ports that the server

listens to</description>

<syntax>Listen [<var>IP-address</var>:]<var>portnumber</var> [<var>protocol</var>]</syntax>

<contextlist><context>server config</context></contextlist>

<modulelist><module>mpm_netware</module><module>mpm_winnt</module>

<module>mpmt_os2</module>

<module>prefork</module><module>worker</module>

<module>event</module>

</modulelist>

<compatibility>Required directive since Apache HTTP Server 2.0<br/>

The <var>protocol</var> argument was added in 2.1.5</compatibility>

<usage>

<p>The <directive>Listen</directive> directive instructs Apache httpd to

listen to only specific IP addresses or ports; by default it

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 httpd.</p>

<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 <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>

<example>

Listen 80<br />

Listen 8000

</example>

<p>To make the server accept connections on two specified

interfaces and port numbers, use </p>

<example>

Listen 192.170.2.1:80<br />

Listen 192.170.2.5:8000

</example>

<p>IPv6 addresses must be surrounded in square brackets, as in the

following example:</p>

<example>

Listen [2001:db8::a00:20ff:fea7:ccea]:80

</example>

<p>The optional <var>protocol</var> argument is not required for most

configurations. If not specified, <code>https</code> is the default for

port 443 and <code>http</code> the default for all other ports. The

protocol is used to determine which module should handle a request, and

to apply protocol specific optimizations with the

<directive module="core">AcceptFilter</directive> directive.</p>

<p>You only need to set the protocol if you are running on non-standard

ports. For example, running an <code>https</code> site on port 8443:</p>

<example>

Listen 192.170.2.1:8443 https

</example>

<note><title>Error condition</title>

Multiple <directive>Listen</directive> directives for the same ip

address and port will result in an <code>Address already in use</code>

error message.

</note>

</usage>

<seealso><a href="/dns-caveats.html">DNS Issues</a></seealso>

<seealso><a href="/bind.html">Setting which addresses and ports Apache HTTP Server

uses</a></seealso>

<seealso><a

href="http://wiki.apache.org/httpd/CouldNotBindToAddress">Further

discussion of the <code>Address already in use</code> error message,

including other causes.</a></seealso>

</directivesynopsis>

<directivesynopsis>

<name>ListenBackLog</name>

<description>Maximum length of the queue of pending connections</description>

<syntax>ListenBacklog <var>backlog</var></syntax>

<default>ListenBacklog 511</default>

<contextlist><context>server config</context></contextlist>

<modulelist>

<module>mpm_netware</module><module>mpm_winnt</module>

<module>mpmt_os2</module><module>prefork</module>

<module>worker</module></modulelist>

<usage>

<p>The maximum length of the queue of pending connections.

Generally no tuning is needed or desired, however on some

systems it is desirable to increase this when under a TCP SYN

flood attack. See the backlog parameter to the

<code>listen(2)</code> system call.</p>

<p>This will often be limited to a smaller number by the

operating system. This varies from OS to OS. Also note that

many OSes do not use exactly what is specified as the backlog,

but use a number based on (but normally larger than) what is

set.</p>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>MaxClients</name>

<description>Maximum number of connections that will be processed

simultaneously</description>

<syntax>MaxClients <var>number</var></syntax>

<default>See usage for details</default>

<contextlist><context>server config</context></contextlist>

<modulelist><module>prefork</module><module>worker</module>

</modulelist>

<usage>

<p>The <directive>MaxClients</directive> directive sets the limit

on the number of simultaneous requests that will be served. Any

connection attempts over the <directive>MaxClients</directive>

limit will normally be queued, up to a number based on the

<directive module="mpm_common">ListenBacklog</directive>

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 (<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 <code>256</code>; to increase it, you must also raise

<directive module="mpm_common">ServerLimit</directive>.</p>

<p>For threaded and hybrid servers (<em>e.g.</em> <module>event</module>

or <module>worker</module>) <directive>MaxClients</directive> restricts

the total number of threads that will be available to serve clients.

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 <code>free()</code></description>

<syntax>MaxMemFree <var>KBytes</var></syntax>

<default>MaxMemFree 0</default>

<contextlist><context>server config</context></contextlist>

<modulelist><module>mpm_netware</module><module>prefork</module>

<module>worker</module><module>mpm_winnt</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 <code>free()</code>. When not set, or when set

to zero, the threshold will be set to unlimited.</p>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>MaxConnectionsPerChild</name>

<description>Limit on the number of connections that an individual child server

will handle during its life</description>

<syntax>MaxConnectionsPerChild <var>number</var></syntax>

<default>MaxConnectionsPerChild 0</default>

<contextlist><context>server config</context></contextlist>

<modulelist><module>mpm_netware</module>

<module>mpm_winnt</module><module>mpmt_os2</module>

<module>prefork</module><module>worker</module></modulelist>

<compatibility>Available Apache HTTP Server 2.3.9 and later. The old name

<code>MaxRequestsPerChild</code> is still supported.</compatibility>

<usage>

<p>The <directive>MaxConnectionsPerChild</directive> directive sets

the limit on the number of connections that an individual child

server process will handle. After

<directive>MaxConnectionsPerChild</directive> connections, the child

process will die. If <directive>MaxConnectionsPerChild</directive> is

<code>0</code>, then the process will never expire.</p>

<p>Setting <directive>MaxConnectionsPerChild</directive> to a

non-zero value limits the amount of memory that process can consume

by (accidental) memory leakage.</p>

</usage>

</directivesynopsis>

<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>mpmt_os2</module>

<module>worker</module></modulelist>

<usage>

<p>Maximum number of idle threads. Different MPMs deal with this

directive differently.</p>

<p>For <module>worker</module>, the default is

<code>MaxSpareThreads 250</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>mpm_netware</module> the default is

<code>MaxSpareThreads 100</code>. Since this MPM runs a

single-process, the spare thread count is also server-wide.</p>

<p><module>mpmt_os2</module> works

similar to <module>mpm_netware</module>. 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 httpd will correct the given value automatically

according to the following rules:</p>

<ul>

<li><module>mpm_netware</module> wants the value to be greater than

<directive module="mpm_common">MinSpareThreads</directive>.</li>

<li>For <module>worker</module>, the value must be greater or equal

to 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>

<seealso><directive module="prefork">MaxSpareServers</directive></seealso>

</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>mpmt_os2</module>

<module>worker</module></modulelist>

<usage>

<p>Minimum number of idle threads to handle request spikes.

Different MPMs deal with this directive

differently.</p>

<p><module>worker</module> uses a default of <code>MinSpareThreads

75</code> and deals 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 <var>number</var>.</p>

<p><module>mpm_netware</module> uses a default of

<code>MinSpareThreads 10</code> and, since it is a single-process

MPM, tracks this on a server-wide bases.</p>

<p><module>mpmt_os2</module> works

similar to <module>mpm_netware</module>. 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>

<seealso><directive module="prefork">MinSpareServers</directive></seealso>

</directivesynopsis>

<directivesynopsis>

<name>ScoreBoardFile</name>

<description>Location of the file used to store coordination data for

the child processes</description>

<syntax>ScoreBoardFile <var>file-path</var></syntax>

<default>ScoreBoardFile logs/apache_status</default>

<contextlist><context>server config</context></contextlist>

<modulelist><module>mpm_winnt</module><module>prefork</module>

<module>worker</module></modulelist>

<usage>

<p>Apache HTTP Server uses a scoreboard to communicate between its parent

and child processes. Some architectures require a file to facilitate

this communication. If the file is left unspecified, Apache httpd first

attempts to create the scoreboard entirely in memory (using anonymous

shared memory) and, failing that, will attempt to create the file on

disk (using file-based shared memory). Specifying this directive causes

Apache httpd to always create the file on the disk.</p>

<example><title>Example</title>

ScoreBoardFile /var/run/apache_status

</example>

<p>File-based shared memory is useful for third-party applications

that require direct access to the scoreboard.</p>

<p>If you use a <directive>ScoreBoardFile</directive> then

you may see improved speed by placing it on a RAM disk. But be

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 HTTP Server</a></seealso>

</directivesynopsis>

<directivesynopsis>

<name>ReceiveBufferSize</name>

<description>TCP receive buffer size</description>

<syntax>ReceiveBufferSize <var>bytes</var></syntax>

<default>ReceiveBufferSize 0</default>

<contextlist><context>server config</context></contextlist>

<modulelist><module>mpm_netware</module><module>mpm_winnt</module>

<module>mpmt_os2</module><module>prefork</module>

<module>worker</module></modulelist>

<usage>

<p>The server will set the TCP receive buffer size to the number of

bytes specified.</p>

<p>If set to the value of <code>0</code>, the server will use the

OS default.</p>

</usage>

</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>mpm_netware</module><module>mpm_winnt</module>

<module>mpmt_os2</module><module>prefork</module>

<module>worker</module></modulelist>

<usage>

<p>Sets the server's TCP send buffer size to the number of bytes

specified. It is often useful to set this past the OS's standard

default value on high speed, high latency conections

(<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

default value provided by your OS.</p>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>ServerLimit</name>

<description>Upper limit on configurable number of processes</description>

<syntax>ServerLimit <var>number</var></syntax>

<default>See usage for details</default>

<contextlist><context>server config</context></contextlist>

<modulelist><module>prefork</module><module>worker</module>

</modulelist>

<usage>

<p>For the <module>prefork</module> MPM, this directive sets the

maximum configured value for <directive

module="mpm_common">MaxClients</directive> for the lifetime of the

Apache httpd process. For the <module>worker</module> MPM, this directive

in combination with <directive

module="mpm_common">ThreadLimit</directive> sets

the maximum configured value for <directive

module="mpm_common">MaxClients</directive> for the lifetime of the

Apache httpd process. Any attempts to change this directive during a

restart will be ignored, but <directive

module="mpm_common">MaxClients</directive> can be modified during

a restart.</p>

<p>Special care must be taken when using this directive. If

<directive>ServerLimit</directive> is set to a value much higher

than necessary, extra, unused shared memory will be allocated. If

both <directive>ServerLimit</directive> and <directive

module="mpm_common">MaxClients</directive> are set to values

higher than the system can handle, Apache httpd may not start or the

system may become unstable.</p>

<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 (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 <module>worker</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 (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>

<note><title>Note</title>

<p>There is a hard limit of <code>ServerLimit 20000</code> compiled

into the server (for the <module>prefork</module> MPM 200000). This is

intended to avoid nasty effects caused by typos. To increase it

even further past this limit, you will need to modify the value of

MAX_SERVER_LIMIT in the mpm source file and rebuild the server.</p>

</note>

</usage>

<seealso><a href="/stopping.html">Stopping and Restarting Apache HTTP Server</a></seealso>

</directivesynopsis>

<directivesynopsis>

<name>StartServers</name>

<description>Number of child server processes created at startup</description>

<syntax>StartServers <var>number</var></syntax>

<default>See usage for details</default>

<contextlist><context>server config</context></contextlist>

<modulelist><module>mpmt_os2</module>

<module>prefork</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, (see

<directive module="mpm_common">MinSpareThreads</directive>,

<directive module="mpm_common">MaxSpareThreads</directive>,

<directive module="prefork">MinSpareServers</directive>, <directive

module="prefork">MaxSpareServers</directive>)

there is usually little reason to adjust this parameter.</p>

<p>The default value differs from MPM to MPM. <module>worker</module>

defaults to <code>StartServers 3</code>; <module>prefork</module>

defaults to <code>5</code>; <module>mpmt_os2</module> defaults to

<code>2</code>.</p>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>StartThreads</name>

<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></modulelist>

<usage>

<p>Number of threads created on startup. As the

number of threads is dynamically controlled depending on the

load, (see

<directive module="mpm_common">MinSpareThreads</directive>,

<directive module="mpm_common">MaxSpareThreads</directive>,

<directive module="prefork">MinSpareServers</directive>, <directive

module="prefork">MaxSpareServers</directive>)

there is usually little reason to adjust this

parameter.</p>

<p>For <module>mpm_netware</module> the default is

<code>StartThreads 50</code> and, since there is only a single

process, this is the total number of threads created at startup to

serve requests.</p>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>ThreadLimit</name>

<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>

<compatibility>Available for <module>mpm_winnt</module> in Apache HTTP Server 2.0.41

and later</compatibility>

<usage>

<p>This directive sets the maximum configured value for <directive

module="mpm_common">ThreadsPerChild</directive> for the lifetime

of the Apache httpd process. Any attempts to change this directive

during a restart will be ignored, but <directive

module="mpm_common">ThreadsPerChild</directive> can be modified

during a restart up to the value of this directive.</p>

<p>Special care must be taken when using this directive. If

<directive>ThreadLimit</directive> is set to a value much higher

than <directive module="mpm_common">ThreadsPerChild</directive>,

extra unused shared memory will be allocated. If both

<directive>ThreadLimit</directive> and <directive

module="mpm_common">ThreadsPerChild</directive> are set to values

higher than the system can handle, Apache httpd may not start or the

system may become unstable. Do not set the value of this directive

any higher than your greatest predicted setting of <directive

module="mpm_common">ThreadsPerChild</directive> for the

current run of Apache httpd.</p>

<p>The default value for <directive>ThreadLimit</directive> is

<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. To increase it even further past this limit, you

will need to modify the value of MAX_THREAD_LIMIT in the mpm

source file and rebuild the server.</p>

</note>

</usage>

</directivesynopsis>

<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>mpm_winnt</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 <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 <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>

<directivesynopsis>

<name>ThreadStackSize</name>

<description>The size in bytes of the stack used by threads handling

client connections</description>

<syntax>ThreadStackSize <var>size</var></syntax>

<default>65536 on NetWare; varies on other operating systems</default>

<contextlist><context>server config</context></contextlist>

<modulelist><module>mpm_netware</module>

<module>mpm_winnt</module><module>worker</module><module>event</module>

</modulelist>

<compatibility>Available in Apache HTTP Server 2.1 and later</compatibility>

<usage>

<p>The <directive>ThreadStackSize</directive> directive sets the

size of the stack (for autodata) of threads which handle client

connections and call modules to help process those connections.

In most cases the operating system default for stack size is

reasonable, but there are some conditions where it may need to be

adjusted:</p>

<ul>

<li>On platforms with a relatively small default thread stack size

(e.g., HP-UX), Apache httpd may crash when using some third-party modules

which use a relatively large amount of autodata storage. Those

same modules may have worked fine on other platforms where the

default thread stack size is larger. This type of crash is

resolved by setting <directive>ThreadStackSize</directive> to a

value higher than the operating system default. This type of

adjustment is necessary only if the provider of the third-party

module specifies that it is required, or if diagnosis of an Apache httpd

crash indicates that the thread stack size was too small.</li>

<li>On platforms where the default thread stack size is

significantly larger than necessary for the web server

configuration, a higher number of threads per child process

will be achievable if <directive>ThreadStackSize</directive> is

set to a value lower than the operating system default. This type

of adjustment should only be made in a test environment which allows

the full set of web server processing can be exercised, as there

may be infrequent requests which require more stack to process.

The minimum required stack size strongly depends on the modules

used, but any change in the web server configuration can invalidate

the current <directive>ThreadStackSize</directive> setting.</li>

</ul>

<note>It is recommended to not reduce <directive>ThreadStackSize</directive>

unless a high number of threads per child process is needed. On some

platforms (including Linux), a setting of 128000 is already too low and

causes crashes with some common modules.</note>

</usage>

</directivesynopsis>

</modulesynopsis>