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15 <p class="apache">Apache HTTP Server Version 2.3</p>
16 <img alt="" src="./images/feather.gif" /></div>
17 <div class="up"><a href="./"><img title="<-" alt="<-" src="./images/left.gif" /></a></div>
19 <a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="./">Version 2.3</a></div><div id="page-content"><div id="preamble"><h1>Stopping and Restarting Apache HTTP Server</h1>
21 <p><span>Available Languages: </span><a href="./de/stopping.html" hreflang="de" rel="alternate" title="Deutsch"> de </a> |
22 <a href="./en/stopping.html" title="English"> en </a> |
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30 <p>This document covers stopping and restarting Apache HTTP Server on
31 Unix-like systems. Windows NT, 2000 and XP users should see
32 <a href="platform/windows.html#winsvc">Running httpd as a
33 Service</a> and Windows 9x and ME users should see <a href="platform/windows.html#wincons">Running httpd as a
34 Console Application</a> for information on how to control
35 httpd on those platforms.</p>
37 <div id="quickview"><ul id="toc"><li><img alt="" src="./images/down.gif" /> <a href="#introduction">Introduction</a></li>
38 <li><img alt="" src="./images/down.gif" /> <a href="#term">Stop Now</a></li>
39 <li><img alt="" src="./images/down.gif" /> <a href="#graceful">Graceful Restart</a></li>
40 <li><img alt="" src="./images/down.gif" /> <a href="#hup">Restart Now</a></li>
41 <li><img alt="" src="./images/down.gif" /> <a href="#gracefulstop">Graceful Stop</a></li>
42 </ul><h3>See also</h3><ul class="seealso"><li><code class="program"><a href="./programs/httpd.html">httpd</a></code></li><li><code class="program"><a href="./programs/apachectl.html">apachectl</a></code></li><li><a href="invoking.html">Starting</a></li></ul></div>
43 <div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
45 <h2><a name="introduction" id="introduction">Introduction</a></h2>
47 <p>In order to stop or restart the Apache HTTP Server, you must send a signal to
48 the running <code class="program"><a href="./programs/httpd.html">httpd</a></code> processes. There are two ways to
49 send the signals. First, you can use the unix <code>kill</code>
50 command to directly send signals to the processes. You will
51 notice many <code class="program"><a href="./programs/httpd.html">httpd</a></code> executables running on your system,
52 but you should not send signals to any of them except the parent,
53 whose pid is in the <code class="directive"><a href="./mod/mpm_common.html#pidfile">PidFile</a></code>. That is to say you
54 shouldn't ever need to send signals to any process except the
55 parent. There are four signals that you can send the parent:
56 <code><a href="#term">TERM</a></code>,
57 <code><a href="#graceful">USR1</a></code>,
58 <code><a href="#hup">HUP</a></code>, and
59 <code><a href="#gracefulstop">WINCH</a></code>, which
60 will be described in a moment.</p>
62 <p>To send a signal to the parent you should issue a command
65 <div class="example"><p><code>kill -TERM `cat /usr/local/apache2/logs/httpd.pid`</code></p></div>
67 <p>The second method of signaling the <code class="program"><a href="./programs/httpd.html">httpd</a></code> processes
68 is to use the <code>-k</code> command line options: <code>stop</code>,
69 <code>restart</code>, <code>graceful</code> and <code>graceful-stop</code>,
70 as described below. These are arguments to the <code class="program"><a href="./programs/httpd.html">httpd</a></code> binary, but we recommend that
71 you send them using the <code class="program"><a href="./programs/apachectl.html">apachectl</a></code> control script, which
72 will pass them through to <code class="program"><a href="./programs/httpd.html">httpd</a></code>.</p>
74 <p>After you have signaled <code class="program"><a href="./programs/httpd.html">httpd</a></code>, you can read about
75 its progress by issuing:</p>
77 <div class="example"><p><code>tail -f /usr/local/apache2/logs/error_log</code></p></div>
79 <p>Modify those examples to match your <code class="directive"><a href="./mod/core.html#serverroot">ServerRoot</a></code> and <code class="directive"><a href="./mod/mpm_common.html#pidfile">PidFile</a></code> settings.</p>
80 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
82 <h2><a name="term" id="term">Stop Now</a></h2>
84 <dl><dt>Signal: TERM</dt>
85 <dd><code>apachectl -k stop</code></dd>
88 <p>Sending the <code>TERM</code> or <code>stop</code> signal to
89 the parent causes it to immediately attempt to kill off all of its
90 children. It may take it several seconds to complete killing off
91 its children. Then the parent itself exits. Any requests in
92 progress are terminated, and no further requests are served.</p>
93 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
95 <h2><a name="graceful" id="graceful">Graceful Restart</a></h2>
97 <dl><dt>Signal: USR1</dt>
98 <dd><code>apachectl -k graceful</code></dd>
101 <p>The <code>USR1</code> or <code>graceful</code> signal causes
102 the parent process to <em>advise</em> the children to exit after
103 their current request (or to exit immediately if they're not
104 serving anything). The parent re-reads its configuration files and
105 re-opens its log files. As each child dies off the parent replaces
106 it with a child from the new <em>generation</em> of the
107 configuration, which begins serving new requests immediately.</p>
109 <p>This code is designed to always respect the process control
110 directive of the MPMs, so the number of processes and threads
111 available to serve clients will be maintained at the appropriate
112 values throughout the restart process. Furthermore, it respects
113 <code class="directive"><a href="./mod/mpm_common.html#startservers">StartServers</a></code> in the
114 following manner: if after one second at least <code class="directive"><a href="./mod/mpm_common.html#startservers">StartServers</a></code> new children have not
115 been created, then create enough to pick up the slack. Hence the
116 code tries to maintain both the number of children appropriate for
117 the current load on the server, and respect your wishes with the
118 <code class="directive"><a href="./mod/mpm_common.html#startservers">StartServers</a></code>
121 <p>Users of <code class="module"><a href="./mod/mod_status.html">mod_status</a></code>
122 will notice that the server statistics are <strong>not</strong>
123 set to zero when a <code>USR1</code> is sent. The code was
124 written to both minimize the time in which the server is unable
125 to serve new requests (they will be queued up by the operating
126 system, so they're not lost in any event) and to respect your
127 tuning parameters. In order to do this it has to keep the
128 <em>scoreboard</em> used to keep track of all children across
131 <p>The status module will also use a <code>G</code> to indicate
132 those children which are still serving requests started before
133 the graceful restart was given.</p>
135 <p>At present there is no way for a log rotation script using
136 <code>USR1</code> to know for certain that all children writing
137 the pre-restart log have finished. We suggest that you use a
138 suitable delay after sending the <code>USR1</code> signal
139 before you do anything with the old log. For example if most of
140 your hits take less than 10 minutes to complete for users on
141 low bandwidth links then you could wait 15 minutes before doing
142 anything with the old log.</p>
145 <p>When you issue a restart, a syntax check is first run, to
146 ensure that there are no errors in the configuration files.
147 If your configuration file has errors in it, you will get an
148 error message about that syntax error, and the server will refuse to
149 restart. This avoids the situation where the server halts and then
150 cannot restart, leaving you with a non-functioning server.</p>
152 <p>This still will not
153 guarantee that the server will restart correctly. To check the
154 semantics of the configuration files as well as the syntax, you
155 can try starting <code class="program"><a href="./programs/httpd.html">httpd</a></code> as a non-root user. If there
156 are no errors it will attempt to open its sockets and logs and fail
157 because it's not root (or because the currently running
158 <code class="program"><a href="./programs/httpd.html">httpd</a></code> already has those ports bound). If it fails
159 for any other reason then it's probably a config file error and the error
160 should be fixed before issuing the graceful restart.</p></div>
161 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
162 <div class="section">
163 <h2><a name="hup" id="hup">Restart Now</a></h2>
165 <dl><dt>Signal: HUP</dt>
166 <dd><code>apachectl -k restart</code></dd>
169 <p>Sending the <code>HUP</code> or <code>restart</code> signal to
170 the parent causes it to kill off its children like in
171 <code>TERM</code>, but the parent doesn't exit. It re-reads its
172 configuration files, and re-opens any log files. Then it spawns a
173 new set of children and continues serving hits.</p>
175 <p>Users of <code class="module"><a href="./mod/mod_status.html">mod_status</a></code>
176 will notice that the server statistics are set to zero when a
177 <code>HUP</code> is sent.</p>
179 <div class="note">As with a graceful restart, a syntax check is run before the
180 restart is attempted. If your configuration file has errors in it, the
181 restart will not be attempted, and you will receive notification of the
182 syntax error(s).</div>
183 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
184 <div class="section">
185 <h2><a name="gracefulstop" id="gracefulstop">Graceful Stop</a></h2>
187 <dl><dt>Signal: WINCH</dt>
188 <dd><code>apachectl -k graceful-stop</code></dd>
191 <p>The <code>WINCH</code> or <code>graceful-stop</code> signal causes
192 the parent process to <em>advise</em> the children to exit after
193 their current request (or to exit immediately if they're not
194 serving anything). The parent will then remove its <code class="directive"><a href="./mod/mpm_common.html#pidfile">PidFile</a></code> and cease listening on
195 all ports. The parent will continue to run, and monitor children
196 which are handling requests. Once all children have finalised
197 and exited or the timeout specified by the <code class="directive"><a href="./mod/mpm_common.html#gracefulshutdowntimeout">GracefulShutdownTimeout</a></code> has been
198 reached, the parent will also exit. If the timeout is reached,
199 any remaining children will be sent the <code>TERM</code> signal
200 to force them to exit.</p>
202 <p>A <code>TERM</code> signal will immediately terminate the
203 parent process and all children when in the "graceful" state. However
204 as the <code class="directive"><a href="./mod/mpm_common.html#pidfile">PidFile</a></code> will
205 have been removed, you will not be able to use
206 <code>apachectl</code> or <code>httpd</code> to send this signal.</p>
208 <div class="note"><p>The <code>graceful-stop</code> signal allows you to run multiple
209 identically configured instances of <code class="program"><a href="./programs/httpd.html">httpd</a></code> at the
210 same time. This is a powerful feature when performing graceful
211 upgrades of httpd, however it can also cause deadlocks and race
212 conditions with some configurations.</p>
214 <p>Care has been taken to ensure that on-disk files such as lock files
215 (<code class="directive"><a href="./mod/core.html#mutex">Mutex</a></code>) and Unix socket files
216 (<code class="directive"><a href="./mod/mod_cgid.html#scriptsock">ScriptSock</a></code>) contain the server
217 PID, and should coexist without problem. However, if a configuration
218 directive, third-party module or persistent CGI utilises any other on-disk
219 lock or state files, care should be taken to ensure that multiple running
220 instances of <code class="program"><a href="./programs/httpd.html">httpd</a></code> do not clobber each other's files.</p>
222 <p>You should also be wary of other potential race conditions, such as
223 using <code class="program"><a href="./programs/rotatelogs.html">rotatelogs</a></code> style piped logging. Multiple running
224 instances of <code class="program"><a href="./programs/rotatelogs.html">rotatelogs</a></code> attempting to rotate the same
225 logfiles at the same time may destroy each other's logfiles.</p></div>
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236 <p class="apache">Copyright 2011 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
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