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 <manualpage metafile="stopping.xml.meta">

   <title>Stopping and Restarting Apache HTTP Server</title>

 <summary>
     <p>This document covers stopping and restarting Apache HTTP Server on
     Unix-like systems. Windows NT, 2000 and XP users should see
     <a href="platform/windows.html#winsvc">Running httpd as a
     Service</a> and Windows 9x and ME users should see <a
     href="platform/windows.html#wincons">Running httpd as a
     Console Application</a> for information on how to control
     httpd on those platforms.</p>
 </summary>

 <seealso><program>httpd</program></seealso>
 <seealso><program>apachectl</program></seealso>
 <seealso><a href="invoking.html">Starting</a></seealso>

 <section id="introduction"><title>Introduction</title>

     <p>In order to stop or restart the Apache HTTP Server, you must send a signal to
     the running <program>httpd</program> processes.  There are two ways to
     send the signals.  First, you can use the unix <code>kill</code>
     command to directly send signals to the processes. You will
     notice many <program>httpd</program> executables running on your system,
     but you should not send signals to any of them except the parent,
     whose pid is in the <directive
     module="mpm_common">PidFile</directive>. That is to say you
     shouldn't ever need to send signals to any process except the
     parent. There are four signals that you can send the parent:
     <code><a href="#term">TERM</a></code>,
     <code><a href="#graceful">USR1</a></code>,
     <code><a href="#hup">HUP</a></code>, and
     <code><a href="#gracefulstop">WINCH</a></code>, which
     will be described in a moment.</p>

     <p>To send a signal to the parent you should issue a command
     such as:</p>

 <example>kill -TERM `cat /usr/local/apache2/logs/httpd.pid`</example>

     <p>The second method of signaling the <program>httpd</program> processes
     is to use the <code>-k</code> command line options: <code>stop</code>,
     <code>restart</code>, <code>graceful</code> and <code>graceful-stop</code>,
     as described below.  These are arguments to the <program>
     httpd</program> binary, but we recommend that
     you send them using the <program>apachectl</program> control script, which
     will pass them through to <program>httpd</program>.</p>

     <p>After you have signaled <program>httpd</program>, you can read about
     its progress by issuing:</p>

 <example>tail -f /usr/local/apache2/logs/error_log</example>

     <p>Modify those examples to match your <directive
     module="core">ServerRoot</directive> and <directive
     module="mpm_common">PidFile</directive> settings.</p>
 </section>

 <section id="term"><title>Stop Now</title>

 <dl><dt>Signal: TERM</dt>
 <dd><code>apachectl -k stop</code></dd>
 </dl>

     <p>Sending the <code>TERM</code> or <code>stop</code> signal to
     the parent causes it to immediately attempt to kill off all of its
     children. It may take it several seconds to complete killing off
     its children.  Then the parent itself exits. Any requests in
     progress are terminated, and no further requests are served.</p>
 </section>

 <section id="graceful"><title>Graceful Restart</title>

 <dl><dt>Signal: USR1</dt>
 <dd><code>apachectl -k graceful</code></dd>
 </dl>

     <p>The <code>USR1</code> or <code>graceful</code> signal causes
     the parent process to <em>advise</em> the children to exit after
     their current request (or to exit immediately if they're not
     serving anything). The parent re-reads its configuration files and
     re-opens its log files. As each child dies off the parent replaces
     it with a child from the new <em>generation</em> of the
     configuration, which begins serving new requests immediately.</p>

     <p>This code is designed to always respect the process control
     directive of the MPMs, so the number of processes and threads
     available to serve clients will be maintained at the appropriate
     values throughout the restart process.  Furthermore, it respects
     <directive module="mpm_common">StartServers</directive> in the
     following manner: if after one second at least <directive
     module="mpm_common">StartServers</directive> new children have not
     been created, then create enough to pick up the slack. Hence the
     code tries to maintain both the number of children appropriate for
     the current load on the server, and respect your wishes with the
     <directive module="mpm_common">StartServers</directive>
     parameter.</p>

     <p>Users of <module>mod_status</module>
     will notice that the server statistics are <strong>not</strong>
     set to zero when a <code>USR1</code> is sent. The code was
     written to both minimize the time in which the server is unable
     to serve new requests (they will be queued up by the operating
     system, so they're not lost in any event) and to respect your
     tuning parameters. In order to do this it has to keep the
     <em>scoreboard</em> used to keep track of all children across
     generations.</p>

     <p>The status module will also use a <code>G</code> to indicate
     those children which are still serving requests started before
     the graceful restart was given.</p>

     <p>At present there is no way for a log rotation script using
     <code>USR1</code> to know for certain that all children writing
     the pre-restart log have finished. We suggest that you use a
     suitable delay after sending the <code>USR1</code> signal
     before you do anything with the old log. For example if most of
     your hits take less than 10 minutes to complete for users on
     low bandwidth links then you could wait 15 minutes before doing
     anything with the old log.</p>

     <note>
     <p>When you issue a restart, a syntax check is first run, to
     ensure that there are no errors in the configuration files.
     If your configuration file has errors in it, you will get an
     error message about that syntax error, and the server will refuse to
     restart. This avoids the situation where the server halts and then
     cannot restart, leaving you with a non-functioning server.</p>

     <p>This still will not
     guarantee that the server will restart correctly. To check the
     semantics of the configuration files as well as the syntax, you
     can try starting <program>httpd</program> as a non-root user. If there
     are no errors it will attempt to open its sockets and logs and fail
     because it's not root (or because the currently running
     <program>httpd</program> already has those ports bound). If it fails
     for any other reason then it's probably a config file error and the error
     should be fixed before issuing the graceful restart.</p></note>
 </section>

 <section id="hup"><title>Restart Now</title>

 <dl><dt>Signal: HUP</dt>
 <dd><code>apachectl -k restart</code></dd>
 </dl>

     <p>Sending the <code>HUP</code> or <code>restart</code> signal to
     the parent causes it to kill off its children like in
     <code>TERM</code>, but the parent doesn't exit. It re-reads its
     configuration files, and re-opens any log files. Then it spawns a
     new set of children and continues serving hits.</p>

     <p>Users of <module>mod_status</module>
     will notice that the server statistics are set to zero when a
     <code>HUP</code> is sent.</p>

 <note>As with a graceful restart, a syntax check is run before the
 restart is attempted. If your configuration file has errors in it, the
 restart will not be attempted, and you will receive notification of the
 syntax error(s).</note>
 </section>

 <section id="gracefulstop"><title>Graceful Stop</title>

 <dl><dt>Signal: WINCH</dt>
 <dd><code>apachectl -k graceful-stop</code></dd>
 </dl>

     <p>The <code>WINCH</code> or <code>graceful-stop</code> signal causes
     the parent process to <em>advise</em> the children to exit after
     their current request (or to exit immediately if they're not
     serving anything). The parent will then remove its <directive
     module="mpm_common">PidFile</directive> and cease listening on
     all ports. The parent will continue to run, and monitor children
     which are handling requests. Once all children have finalised
     and exited or the timeout specified by the <directive
     module="mpm_common">GracefulShutdownTimeout</directive> has been
     reached, the parent will also exit.  If the timeout is reached,
     any remaining children will be sent the <code>TERM</code> signal
     to force them to exit.</p>

     <p>A <code>TERM</code> signal will immediately terminate the
     parent process and all children when in the "graceful" state. However
     as the <directive module="mpm_common">PidFile</directive> will
     have been removed, you will not be able to use
     <code>apachectl</code> or <code>httpd</code> to send this signal.</p>

     <note><p>The <code>graceful-stop</code> signal allows you to run multiple
     identically configured instances of <program>httpd</program> at the
     same time. This is a powerful feature when performing graceful
     upgrades of httpd, however it can also cause deadlocks and race
     conditions with some configurations.</p>

     <p>Care has been taken to ensure that on-disk files such as lock files
     (<directive module="core">Mutex</directive>) and Unix socket files
     (<directive module="mod_cgid">ScriptSock</directive>) contain the server
     PID, and should coexist without problem. However, if a configuration
     directive, third-party module or persistent CGI utilises any other on-disk
     lock or  state files, care should be taken to ensure that multiple running
     instances of <program>httpd</program> do not clobber each other's files.</p>

     <p>You should also be wary of other potential race conditions, such as
     using <program>rotatelogs</program> style piped logging. Multiple running
     instances of <program>rotatelogs</program> attempting to rotate the same
     logfiles at the same time may destroy each other's logfiles.</p></note>
 </section>

 </manualpage>
	<?xml version='1.0' encoding='UTF-8' ?>
	<!DOCTYPE manualpage SYSTEM "./style/manualpage.dtd">
	<?xml-stylesheet type="text/xsl" href="./style/manual.en.xsl"?>
	<!-- $LastChangedRevision$ -->

	<!--
	Licensed to the Apache Software Foundation (ASF) under one or more
	contributor license agreements. See the NOTICE file distributed with
	this work for additional information regarding copyright ownership.
	The ASF licenses this file to You under the Apache License, Version 2.0
	(the "License"); you may not use this file except in compliance with
	the License. You may obtain a copy of the License at

	http://www.apache.org/licenses/LICENSE-2.0

	Unless required by applicable law or agreed to in writing, software
	distributed under the License is distributed on an "AS IS" BASIS,
	WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	See the License for the specific language governing permissions and
	limitations under the License.
	-->

	<manualpage metafile="stopping.xml.meta">

	<title>Stopping and Restarting Apache HTTP Server</title>

	<summary>
	<p>This document covers stopping and restarting Apache HTTP Server on
	Unix-like systems. Windows NT, 2000 and XP users should see
	<a href="platform/windows.html#winsvc">Running httpd as a
	Service</a> and Windows 9x and ME users should see <a
	href="platform/windows.html#wincons">Running httpd as a
	Console Application</a> for information on how to control
	httpd on those platforms.</p>
	</summary>

	<seealso><program>httpd</program></seealso>
	<seealso><program>apachectl</program></seealso>
	<seealso><a href="invoking.html">Starting</a></seealso>

	<section id="introduction"><title>Introduction</title>

	<p>In order to stop or restart the Apache HTTP Server, you must send a signal to
	the running <program>httpd</program> processes. There are two ways to
	send the signals. First, you can use the unix <code>kill</code>
	command to directly send signals to the processes. You will
	notice many <program>httpd</program> executables running on your system,
	but you should not send signals to any of them except the parent,
	whose pid is in the <directive
	module="mpm_common">PidFile</directive>. That is to say you
	shouldn't ever need to send signals to any process except the
	parent. There are four signals that you can send the parent:
	<code><a href="#term">TERM</a></code>,
	<code><a href="#graceful">USR1</a></code>,
	<code><a href="#hup">HUP</a></code>, and
	<code><a href="#gracefulstop">WINCH</a></code>, which
	will be described in a moment.</p>

	<p>To send a signal to the parent you should issue a command
	such as:</p>

	<example>kill -TERM `cat /usr/local/apache2/logs/httpd.pid`</example>

	<p>The second method of signaling the <program>httpd</program> processes
	is to use the <code>-k</code> command line options: <code>stop</code>,
	<code>restart</code>, <code>graceful</code> and <code>graceful-stop</code>,
	as described below. These are arguments to the <program>
	httpd</program> binary, but we recommend that
	you send them using the <program>apachectl</program> control script, which
	will pass them through to <program>httpd</program>.</p>

	<p>After you have signaled <program>httpd</program>, you can read about
	its progress by issuing:</p>

	<example>tail -f /usr/local/apache2/logs/error_log</example>

	<p>Modify those examples to match your <directive
	module="core">ServerRoot</directive> and <directive
	module="mpm_common">PidFile</directive> settings.</p>
	</section>

	<section id="term"><title>Stop Now</title>

	<dl><dt>Signal: TERM</dt>
	<dd><code>apachectl -k stop</code></dd>
	</dl>

	<p>Sending the <code>TERM</code> or <code>stop</code> signal to
	the parent causes it to immediately attempt to kill off all of its
	children. It may take it several seconds to complete killing off
	its children. Then the parent itself exits. Any requests in
	progress are terminated, and no further requests are served.</p>
	</section>

	<section id="graceful"><title>Graceful Restart</title>

	<dl><dt>Signal: USR1</dt>
	<dd><code>apachectl -k graceful</code></dd>
	</dl>

	<p>The <code>USR1</code> or <code>graceful</code> signal causes
	the parent process to <em>advise</em> the children to exit after
	their current request (or to exit immediately if they're not
	serving anything). The parent re-reads its configuration files and
	re-opens its log files. As each child dies off the parent replaces
	it with a child from the new <em>generation</em> of the
	configuration, which begins serving new requests immediately.</p>

	<p>This code is designed to always respect the process control
	directive of the MPMs, so the number of processes and threads
	available to serve clients will be maintained at the appropriate
	values throughout the restart process. Furthermore, it respects
	<directive module="mpm_common">StartServers</directive> in the
	following manner: if after one second at least <directive
	module="mpm_common">StartServers</directive> new children have not
	been created, then create enough to pick up the slack. Hence the
	code tries to maintain both the number of children appropriate for
	the current load on the server, and respect your wishes with the
	<directive module="mpm_common">StartServers</directive>
	parameter.</p>

	<p>Users of <module>mod_status</module>
	will notice that the server statistics are <strong>not</strong>
	set to zero when a <code>USR1</code> is sent. The code was
	written to both minimize the time in which the server is unable
	to serve new requests (they will be queued up by the operating
	system, so they're not lost in any event) and to respect your
	tuning parameters. In order to do this it has to keep the
	<em>scoreboard</em> used to keep track of all children across
	generations.</p>

	<p>The status module will also use a <code>G</code> to indicate
	those children which are still serving requests started before
	the graceful restart was given.</p>

	<p>At present there is no way for a log rotation script using
	<code>USR1</code> to know for certain that all children writing
	the pre-restart log have finished. We suggest that you use a
	suitable delay after sending the <code>USR1</code> signal
	before you do anything with the old log. For example if most of
	your hits take less than 10 minutes to complete for users on
	low bandwidth links then you could wait 15 minutes before doing
	anything with the old log.</p>

	<note>
	<p>When you issue a restart, a syntax check is first run, to
	ensure that there are no errors in the configuration files.
	If your configuration file has errors in it, you will get an
	error message about that syntax error, and the server will refuse to
	restart. This avoids the situation where the server halts and then
	cannot restart, leaving you with a non-functioning server.</p>

	<p>This still will not
	guarantee that the server will restart correctly. To check the
	semantics of the configuration files as well as the syntax, you
	can try starting <program>httpd</program> as a non-root user. If there
	are no errors it will attempt to open its sockets and logs and fail
	because it's not root (or because the currently running
	<program>httpd</program> already has those ports bound). If it fails
	for any other reason then it's probably a config file error and the error
	should be fixed before issuing the graceful restart.</p></note>
	</section>

	<section id="hup"><title>Restart Now</title>

	<dl><dt>Signal: HUP</dt>
	<dd><code>apachectl -k restart</code></dd>
	</dl>

	<p>Sending the <code>HUP</code> or <code>restart</code> signal to
	the parent causes it to kill off its children like in
	<code>TERM</code>, but the parent doesn't exit. It re-reads its
	configuration files, and re-opens any log files. Then it spawns a
	new set of children and continues serving hits.</p>

	<p>Users of <module>mod_status</module>
	will notice that the server statistics are set to zero when a
	<code>HUP</code> is sent.</p>

	<note>As with a graceful restart, a syntax check is run before the
	restart is attempted. If your configuration file has errors in it, the
	restart will not be attempted, and you will receive notification of the
	syntax error(s).</note>
	</section>

	<section id="gracefulstop"><title>Graceful Stop</title>

	<dl><dt>Signal: WINCH</dt>
	<dd><code>apachectl -k graceful-stop</code></dd>
	</dl>

	<p>The <code>WINCH</code> or <code>graceful-stop</code> signal causes
	the parent process to <em>advise</em> the children to exit after
	their current request (or to exit immediately if they're not
	serving anything). The parent will then remove its <directive
	module="mpm_common">PidFile</directive> and cease listening on
	all ports. The parent will continue to run, and monitor children
	which are handling requests. Once all children have finalised
	and exited or the timeout specified by the <directive
	module="mpm_common">GracefulShutdownTimeout</directive> has been
	reached, the parent will also exit. If the timeout is reached,
	any remaining children will be sent the <code>TERM</code> signal
	to force them to exit.</p>

	<p>A <code>TERM</code> signal will immediately terminate the
	parent process and all children when in the "graceful" state. However
	as the <directive module="mpm_common">PidFile</directive> will
	have been removed, you will not be able to use
	<code>apachectl</code> or <code>httpd</code> to send this signal.</p>

	<note><p>The <code>graceful-stop</code> signal allows you to run multiple
	identically configured instances of <program>httpd</program> at the
	same time. This is a powerful feature when performing graceful
	upgrades of httpd, however it can also cause deadlocks and race
	conditions with some configurations.</p>

	<p>Care has been taken to ensure that on-disk files such as lock files
	(<directive module="core">Mutex</directive>) and Unix socket files
	(<directive module="mod_cgid">ScriptSock</directive>) contain the server
	PID, and should coexist without problem. However, if a configuration
	directive, third-party module or persistent CGI utilises any other on-disk
	lock or state files, care should be taken to ensure that multiple running
	instances of <program>httpd</program> do not clobber each other's files.</p>

	<p>You should also be wary of other potential race conditions, such as
	using <program>rotatelogs</program> style piped logging. Multiple running
	instances of <program>rotatelogs</program> attempting to rotate the same
	logfiles at the same time may destroy each other's logfiles.</p></note>
	</section>

	</manualpage>