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8 <title>Stopping and Restarting Apache HTTP Server - Apache HTTP Server Version 2.5</title>
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18 <p class="apache">Apache HTTP Server Version 2.5</p>
19 <img alt="" src="./images/feather.gif" /></div>
20 <div class="up"><a href="./"><img title="<-" alt="<-" src="./images/left.gif" /></a></div>
22 <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 2.5</a></div><div id="page-content"><div id="preamble"><h1>Stopping and Restarting Apache HTTP Server</h1>
24 <p><span>Available Languages: </span><a href="./de/stopping.html" hreflang="de" rel="alternate" title="Deutsch"> de </a> |
25 <a href="./en/stopping.html" title="English"> en </a> |
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33 <p>This document covers stopping and restarting Apache HTTP Server on
34 Unix-like systems. Windows NT, 2000 and XP users should see
35 <a href="platform/windows.html#winsvc">Running httpd as a
36 Service</a> and Windows 9x and ME users should see <a href="platform/windows.html#wincons">Running httpd as a
37 Console Application</a> for information on how to control
38 httpd on those platforms.</p>
40 <div id="quickview"><ul id="toc"><li><img alt="" src="./images/down.gif" /> <a href="#introduction">Introduction</a></li>
41 <li><img alt="" src="./images/down.gif" /> <a href="#term">Stop Now</a></li>
42 <li><img alt="" src="./images/down.gif" /> <a href="#graceful">Graceful Restart</a></li>
43 <li><img alt="" src="./images/down.gif" /> <a href="#hup">Restart Now</a></li>
44 <li><img alt="" src="./images/down.gif" /> <a href="#gracefulstop">Graceful Stop</a></li>
45 </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><ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div>
46 <div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
48 <h2><a name="introduction" id="introduction">Introduction</a></h2>
50 <p>In order to stop or restart the Apache HTTP Server, you must send a signal to
51 the running <code class="program"><a href="./programs/httpd.html">httpd</a></code> processes. There are two ways to
52 send the signals. First, you can use the unix <code>kill</code>
53 command to directly send signals to the processes. You will
54 notice many <code class="program"><a href="./programs/httpd.html">httpd</a></code> executables running on your system,
55 but you should not send signals to any of them except the parent,
56 whose pid is in the <code class="directive"><a href="./mod/mpm_common.html#pidfile">PidFile</a></code>. That is to say you
57 shouldn't ever need to send signals to any process except the
58 parent. There are four signals that you can send the parent:
59 <code><a href="#term">TERM</a></code>,
60 <code><a href="#graceful">USR1</a></code>,
61 <code><a href="#hup">HUP</a></code>, and
62 <code><a href="#gracefulstop">WINCH</a></code>, which
63 will be described in a moment.</p>
65 <p>To send a signal to the parent you should issue a command
68 <div class="example"><p><code>kill -TERM `cat /usr/local/apache2/logs/httpd.pid`</code></p></div>
70 <p>The second method of signaling the <code class="program"><a href="./programs/httpd.html">httpd</a></code> processes
71 is to use the <code>-k</code> command line options: <code>stop</code>,
72 <code>restart</code>, <code>graceful</code> and <code>graceful-stop</code>,
73 as described below. These are arguments to the <code class="program"><a href="./programs/httpd.html">httpd</a></code> binary, but we recommend that
74 you send them using the <code class="program"><a href="./programs/apachectl.html">apachectl</a></code> control script, which
75 will pass them through to <code class="program"><a href="./programs/httpd.html">httpd</a></code>.</p>
77 <p>After you have signaled <code class="program"><a href="./programs/httpd.html">httpd</a></code>, you can read about
78 its progress by issuing:</p>
80 <div class="example"><p><code>tail -f /usr/local/apache2/logs/error_log</code></p></div>
82 <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>
83 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
85 <h2><a name="term" id="term">Stop Now</a></h2>
87 <dl><dt>Signal: TERM</dt>
88 <dd><code>apachectl -k stop</code></dd>
91 <p>Sending the <code>TERM</code> or <code>stop</code> signal to
92 the parent causes it to immediately attempt to kill off all of its
93 children. It may take it several seconds to complete killing off
94 its children. Then the parent itself exits. Any requests in
95 progress are terminated, and no further requests are served.</p>
96 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
98 <h2><a name="graceful" id="graceful">Graceful Restart</a></h2>
100 <dl><dt>Signal: USR1</dt>
101 <dd><code>apachectl -k graceful</code></dd>
104 <p>The <code>USR1</code> or <code>graceful</code> signal causes
105 the parent process to <em>advise</em> the children to exit after
106 their current request (or to exit immediately if they're not
107 serving anything). The parent re-reads its configuration files and
108 re-opens its log files. As each child dies off the parent replaces
109 it with a child from the new <em>generation</em> of the
110 configuration, which begins serving new requests immediately.</p>
112 <p>This code is designed to always respect the process control
113 directive of the MPMs, so the number of processes and threads
114 available to serve clients will be maintained at the appropriate
115 values throughout the restart process. Furthermore, it respects
116 <code class="directive"><a href="./mod/mpm_common.html#startservers">StartServers</a></code> in the
117 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
118 been created, then create enough to pick up the slack. Hence the
119 code tries to maintain both the number of children appropriate for
120 the current load on the server, and respect your wishes with the
121 <code class="directive"><a href="./mod/mpm_common.html#startservers">StartServers</a></code>
124 <p>Users of <code class="module"><a href="./mod/mod_status.html">mod_status</a></code>
125 will notice that the server statistics are <strong>not</strong>
126 set to zero when a <code>USR1</code> is sent. The code was
127 written to both minimize the time in which the server is unable
128 to serve new requests (they will be queued up by the operating
129 system, so they're not lost in any event) and to respect your
130 tuning parameters. In order to do this it has to keep the
131 <em>scoreboard</em> used to keep track of all children across
134 <p>The status module will also use a <code>G</code> to indicate
135 those children which are still serving requests started before
136 the graceful restart was given.</p>
138 <p>At present there is no way for a log rotation script using
139 <code>USR1</code> to know for certain that all children writing
140 the pre-restart log have finished. We suggest that you use a
141 suitable delay after sending the <code>USR1</code> signal
142 before you do anything with the old log. For example if most of
143 your hits take less than 10 minutes to complete for users on
144 low bandwidth links then you could wait 15 minutes before doing
145 anything with the old log.</p>
148 <p>When you issue a restart, a syntax check is first run, to
149 ensure that there are no errors in the configuration files.
150 If your configuration file has errors in it, you will get an
151 error message about that syntax error, and the server will refuse to
152 restart. This avoids the situation where the server halts and then
153 cannot restart, leaving you with a non-functioning server.</p>
155 <p>This still will not
156 guarantee that the server will restart correctly. To check the
157 semantics of the configuration files as well as the syntax, you
158 can try starting <code class="program"><a href="./programs/httpd.html">httpd</a></code> as a non-root user. If there
159 are no errors it will attempt to open its sockets and logs and fail
160 because it's not root (or because the currently running
161 <code class="program"><a href="./programs/httpd.html">httpd</a></code> already has those ports bound). If it fails
162 for any other reason then it's probably a config file error and the error
163 should be fixed before issuing the graceful restart.</p></div>
164 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
165 <div class="section">
166 <h2><a name="hup" id="hup">Restart Now</a></h2>
168 <dl><dt>Signal: HUP</dt>
169 <dd><code>apachectl -k restart</code></dd>
172 <p>Sending the <code>HUP</code> or <code>restart</code> signal to
173 the parent causes it to kill off its children like in
174 <code>TERM</code>, but the parent doesn't exit. It re-reads its
175 configuration files, and re-opens any log files. Then it spawns a
176 new set of children and continues serving hits.</p>
178 <p>Users of <code class="module"><a href="./mod/mod_status.html">mod_status</a></code>
179 will notice that the server statistics are set to zero when a
180 <code>HUP</code> is sent.</p>
182 <div class="note">As with a graceful restart, a syntax check is run before the
183 restart is attempted. If your configuration file has errors in it, the
184 restart will not be attempted, and you will receive notification of the
185 syntax error(s).</div>
186 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
187 <div class="section">
188 <h2><a name="gracefulstop" id="gracefulstop">Graceful Stop</a></h2>
190 <dl><dt>Signal: WINCH</dt>
191 <dd><code>apachectl -k graceful-stop</code></dd>
194 <p>The <code>WINCH</code> or <code>graceful-stop</code> signal causes
195 the parent process to <em>advise</em> the children to exit after
196 their current request (or to exit immediately if they're not
197 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
198 all ports. The parent will continue to run, and monitor children
199 which are handling requests. Once all children have finalised
200 and exited or the timeout specified by the <code class="directive"><a href="./mod/mpm_common.html#gracefulshutdowntimeout">GracefulShutdownTimeout</a></code> has been
201 reached, the parent will also exit. If the timeout is reached,
202 any remaining children will be sent the <code>TERM</code> signal
203 to force them to exit.</p>
205 <p>A <code>TERM</code> signal will immediately terminate the
206 parent process and all children when in the "graceful" state. However
207 as the <code class="directive"><a href="./mod/mpm_common.html#pidfile">PidFile</a></code> will
208 have been removed, you will not be able to use
209 <code>apachectl</code> or <code>httpd</code> to send this signal.</p>
211 <div class="note"><p>The <code>graceful-stop</code> signal allows you to run multiple
212 identically configured instances of <code class="program"><a href="./programs/httpd.html">httpd</a></code> at the
213 same time. This is a powerful feature when performing graceful
214 upgrades of httpd, however it can also cause deadlocks and race
215 conditions with some configurations.</p>
217 <p>Care has been taken to ensure that on-disk files such as lock files
218 (<code class="directive"><a href="./mod/core.html#mutex">Mutex</a></code>) and Unix socket files
219 (<code class="directive"><a href="./mod/mod_cgid.html#scriptsock">ScriptSock</a></code>) contain the server
220 PID, and should coexist without problem. However, if a configuration
221 directive, third-party module or persistent CGI utilises any other on-disk
222 lock or state files, care should be taken to ensure that multiple running
223 instances of <code class="program"><a href="./programs/httpd.html">httpd</a></code> do not clobber each other's files.</p>
225 <p>You should also be wary of other potential race conditions, such as
226 using <code class="program"><a href="./programs/rotatelogs.html">rotatelogs</a></code> style piped logging. Multiple running
227 instances of <code class="program"><a href="./programs/rotatelogs.html">rotatelogs</a></code> attempting to rotate the same
228 logfiles at the same time may destroy each other's logfiles.</p></div>
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238 </div><div class="top"><a href="#page-header"><img src="./images/up.gif" alt="top" /></a></div><div class="section"><h2><a id="comments_section" name="comments_section">Comments</a></h2><div class="warning"><strong>Notice:</strong><br />This is not a Q&A section. Comments placed here should be pointed towards suggestions on improving the documentation or server, and may be removed again by our moderators if they are either implemented or considered invalid/off-topic. Questions on how to manage the Apache HTTP Server should be directed at either our IRC channel, #httpd, on Freenode, or sent to our <a href="http://httpd.apache.org/lists.html">mailing lists</a>.</div>
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