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10 <title>Stopping and Restarting Apache HTTP Server - Apache HTTP Server Version 2.5</title>
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20 <p class="apache">Apache HTTP Server Version 2.5</p>
21 <img alt="" src="./images/feather.png" /></div>
22 <div class="up"><a href="./"><img title="<-" alt="<-" src="./images/left.gif" /></a></div>
24 <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>
26 <p><span>Available Languages: </span><a href="./de/stopping.html" hreflang="de" rel="alternate" title="Deutsch"> de </a> |
27 <a href="./en/stopping.html" title="English"> en </a> |
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35 <p>This document covers stopping and restarting Apache HTTP Server on
36 Unix-like systems. Windows NT, 2000 and XP users should see
37 <a href="platform/windows.html#winsvc">Running httpd as a
38 Service</a> and Windows 9x and ME users should see <a href="platform/windows.html#wincons">Running httpd as a
39 Console Application</a> for information on how to control
40 httpd on those platforms.</p>
42 <div id="quickview"><ul id="toc"><li><img alt="" src="./images/down.gif" /> <a href="#introduction">Introduction</a></li>
43 <li><img alt="" src="./images/down.gif" /> <a href="#term">Stop Now</a></li>
44 <li><img alt="" src="./images/down.gif" /> <a href="#graceful">Graceful Restart</a></li>
45 <li><img alt="" src="./images/down.gif" /> <a href="#hup">Restart Now</a></li>
46 <li><img alt="" src="./images/down.gif" /> <a href="#gracefulstop">Graceful Stop</a></li>
47 </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><li><a href="#comments_section">Comments</a></li></ul></div>
48 <div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
50 <h2><a name="introduction" id="introduction">Introduction</a></h2>
52 <p>In order to stop or restart the Apache HTTP Server, you must send a signal to
53 the running <code class="program"><a href="./programs/httpd.html">httpd</a></code> processes. There are two ways to
54 send the signals. First, you can use the unix <code>kill</code>
55 command to directly send signals to the processes. You will
56 notice many <code class="program"><a href="./programs/httpd.html">httpd</a></code> executables running on your system,
57 but you should not send signals to any of them except the parent,
58 whose pid is in the <code class="directive"><a href="./mod/mpm_common.html#pidfile">PidFile</a></code>. That is to say you
59 shouldn't ever need to send signals to any process except the
60 parent. There are four signals that you can send the parent:
61 <code><a href="#term">TERM</a></code>,
62 <code><a href="#graceful">USR1</a></code>,
63 <code><a href="#hup">HUP</a></code>, and
64 <code><a href="#gracefulstop">WINCH</a></code>, which
65 will be described in a moment.</p>
67 <p>To send a signal to the parent you should issue a command
70 <div class="example"><p><code>kill -TERM `cat /usr/local/apache2/logs/httpd.pid`</code></p></div>
72 <p>The second method of signaling the <code class="program"><a href="./programs/httpd.html">httpd</a></code> processes
73 is to use the <code>-k</code> command line options: <code>stop</code>,
74 <code>restart</code>, <code>graceful</code> and <code>graceful-stop</code>,
75 as described below. These are arguments to the <code class="program"><a href="./programs/httpd.html">httpd</a></code> binary, but we recommend that
76 you send them using the <code class="program"><a href="./programs/apachectl.html">apachectl</a></code> control script, which
77 will pass them through to <code class="program"><a href="./programs/httpd.html">httpd</a></code>.</p>
79 <p>After you have signaled <code class="program"><a href="./programs/httpd.html">httpd</a></code>, you can read about
80 its progress by issuing:</p>
82 <div class="example"><p><code>tail -f /usr/local/apache2/logs/error_log</code></p></div>
84 <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>
85 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
87 <h2><a name="term" id="term">Stop Now</a></h2>
89 <dl><dt>Signal: TERM</dt>
90 <dd><code>apachectl -k stop</code></dd>
93 <p>Sending the <code>TERM</code> or <code>stop</code> signal to
94 the parent causes it to immediately attempt to kill off all of its
95 children. It may take it several seconds to complete killing off
96 its children. Then the parent itself exits. Any requests in
97 progress are terminated, and no further requests are served.</p>
98 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
100 <h2><a name="graceful" id="graceful">Graceful Restart</a></h2>
102 <dl><dt>Signal: USR1</dt>
103 <dd><code>apachectl -k graceful</code></dd>
106 <p>The <code>USR1</code> or <code>graceful</code> signal causes
107 the parent process to <em>advise</em> the children to exit after
108 their current request (or to exit immediately if they're not
109 serving anything). The parent re-reads its configuration files and
110 re-opens its log files. As each child dies off the parent replaces
111 it with a child from the new <em>generation</em> of the
112 configuration, which begins serving new requests immediately.</p>
114 <p>This code is designed to always respect the process control
115 directive of the MPMs, so the number of processes and threads
116 available to serve clients will be maintained at the appropriate
117 values throughout the restart process. Furthermore, it respects
118 <code class="directive"><a href="./mod/mpm_common.html#startservers">StartServers</a></code> in the
119 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
120 been created, then create enough to pick up the slack. Hence the
121 code tries to maintain both the number of children appropriate for
122 the current load on the server, and respect your wishes with the
123 <code class="directive"><a href="./mod/mpm_common.html#startservers">StartServers</a></code>
126 <p>Users of <code class="module"><a href="./mod/mod_status.html">mod_status</a></code>
127 will notice that the server statistics are <strong>not</strong>
128 set to zero when a <code>USR1</code> is sent. The code was
129 written to both minimize the time in which the server is unable
130 to serve new requests (they will be queued up by the operating
131 system, so they're not lost in any event) and to respect your
132 tuning parameters. In order to do this it has to keep the
133 <em>scoreboard</em> used to keep track of all children across
136 <p>The status module will also use a <code>G</code> to indicate
137 those children which are still serving requests started before
138 the graceful restart was given.</p>
140 <p>At present there is no way for a log rotation script using
141 <code>USR1</code> to know for certain that all children writing
142 the pre-restart log have finished. We suggest that you use a
143 suitable delay after sending the <code>USR1</code> signal
144 before you do anything with the old log. For example if most of
145 your hits take less than 10 minutes to complete for users on
146 low bandwidth links then you could wait 15 minutes before doing
147 anything with the old log.</p>
150 <p>When you issue a restart, a syntax check is first run, to
151 ensure that there are no errors in the configuration files.
152 If your configuration file has errors in it, you will get an
153 error message about that syntax error, and the server will refuse to
154 restart. This avoids the situation where the server halts and then
155 cannot restart, leaving you with a non-functioning server.</p>
157 <p>This still will not
158 guarantee that the server will restart correctly. To check the
159 semantics of the configuration files as well as the syntax, you
160 can try starting <code class="program"><a href="./programs/httpd.html">httpd</a></code> as a non-root user. If there
161 are no errors it will attempt to open its sockets and logs and fail
162 because it's not root (or because the currently running
163 <code class="program"><a href="./programs/httpd.html">httpd</a></code> already has those ports bound). If it fails
164 for any other reason then it's probably a config file error and the error
165 should be fixed before issuing the graceful restart.</p></div>
166 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
167 <div class="section">
168 <h2><a name="hup" id="hup">Restart Now</a></h2>
170 <dl><dt>Signal: HUP</dt>
171 <dd><code>apachectl -k restart</code></dd>
174 <p>Sending the <code>HUP</code> or <code>restart</code> signal to
175 the parent causes it to kill off its children like in
176 <code>TERM</code>, but the parent doesn't exit. It re-reads its
177 configuration files, and re-opens any log files. Then it spawns a
178 new set of children and continues serving hits.</p>
180 <p>Users of <code class="module"><a href="./mod/mod_status.html">mod_status</a></code>
181 will notice that the server statistics are set to zero when a
182 <code>HUP</code> is sent.</p>
184 <div class="note">As with a graceful restart, a syntax check is run before the
185 restart is attempted. If your configuration file has errors in it, the
186 restart will not be attempted, and you will receive notification of the
187 syntax error(s).</div>
188 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
189 <div class="section">
190 <h2><a name="gracefulstop" id="gracefulstop">Graceful Stop</a></h2>
192 <dl><dt>Signal: WINCH</dt>
193 <dd><code>apachectl -k graceful-stop</code></dd>
196 <p>The <code>WINCH</code> or <code>graceful-stop</code> signal causes
197 the parent process to <em>advise</em> the children to exit after
198 their current request (or to exit immediately if they're not
199 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
200 all ports. The parent will continue to run, and monitor children
201 which are handling requests. Once all children have finalised
202 and exited or the timeout specified by the <code class="directive"><a href="./mod/mpm_common.html#gracefulshutdowntimeout">GracefulShutdownTimeout</a></code> has been
203 reached, the parent will also exit. If the timeout is reached,
204 any remaining children will be sent the <code>TERM</code> signal
205 to force them to exit.</p>
207 <p>A <code>TERM</code> signal will immediately terminate the
208 parent process and all children when in the "graceful" state. However
209 as the <code class="directive"><a href="./mod/mpm_common.html#pidfile">PidFile</a></code> will
210 have been removed, you will not be able to use
211 <code>apachectl</code> or <code>httpd</code> to send this signal.</p>
213 <div class="note"><p>The <code>graceful-stop</code> signal allows you to run multiple
214 identically configured instances of <code class="program"><a href="./programs/httpd.html">httpd</a></code> at the
215 same time. This is a powerful feature when performing graceful
216 upgrades of httpd, however it can also cause deadlocks and race
217 conditions with some configurations.</p>
219 <p>Care has been taken to ensure that on-disk files such as lock files
220 (<code class="directive"><a href="./mod/core.html#mutex">Mutex</a></code>) and Unix socket files
221 (<code class="directive"><a href="./mod/mod_cgid.html#scriptsock">ScriptSock</a></code>) contain the server
222 PID, and should coexist without problem. However, if a configuration
223 directive, third-party module or persistent CGI utilises any other on-disk
224 lock or state files, care should be taken to ensure that multiple running
225 instances of <code class="program"><a href="./programs/httpd.html">httpd</a></code> do not clobber each other's files.</p>
227 <p>You should also be wary of other potential race conditions, such as
228 using <code class="program"><a href="./programs/rotatelogs.html">rotatelogs</a></code> style piped logging. Multiple running
229 instances of <code class="program"><a href="./programs/rotatelogs.html">rotatelogs</a></code> attempting to rotate the same
230 logfiles at the same time may destroy each other's logfiles.</p></div>
232 <div class="bottomlang">
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234 <a href="./en/stopping.html" title="English"> en </a> |
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240 </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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