1<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" 2 "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> 3<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" 4 "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 5 6<html xmlns="http://www.w3.org/1999/xhtml"> 7 <head> 8 <meta name="generator" content="HTML Tidy, see www.w3.org" /> 9 10 <title>Stopping and Restarting Apache</title> 11 </head> 12 <!-- Background white, links blue (unvisited), navy (visited), red (active) --> 13 14 <body bgcolor="#FFFFFF" text="#000000" link="#0000FF" 15 vlink="#000080" alink="#FF0000"> 16 <div align="CENTER"> 17 <img src="images/sub.gif" alt="[APACHE DOCUMENTATION]" /> 18 19 <h3>Apache HTTP Server</h3> 20 </div> 21 22 23 24 <h1 align="CENTER">Stopping and Restarting Apache</h1> 25 26 <p>You will notice many <code>httpd</code> executables running 27 on your system, but you should not send signals to any of them 28 except the parent, whose pid is in the <a 29 href="mod/core.html#pidfile">PidFile</a>. That is to say you 30 shouldn't ever need to send signals to any process except the 31 parent. There are three signals that you can send the parent: 32 <code>TERM</code>, <code>HUP</code>, and <code>USR1</code>, 33 which will be described in a moment.</p> 34 35 <p>To send a signal to the parent you should issue a command 36 such as:</p> 37 38 <blockquote> 39<pre> 40 kill -TERM `cat /usr/local/apache/logs/httpd.pid` 41</pre> 42 </blockquote> 43 You can read about its progress by issuing: 44 45 <blockquote> 46<pre> 47 tail -f /usr/local/apache/logs/error_log 48</pre> 49 </blockquote> 50 Modify those examples to match your <a 51 href="mod/core.html#serverroot">ServerRoot</a> and <a 52 href="mod/core.html#pidfile">PidFile</a> settings. 53 54 <p>As of Apache 1.3 we provide a script called <a 55 href="programs/apachectl.html">apachectl</a> which can be used 56 to start, stop, and restart Apache. It may need a little 57 customization for your system, see the comments at the top of 58 the script.</p> 59 60 <h3>TERM Signal: stop now</h3> 61 62 <p>Sending the <code>TERM</code> signal to the parent causes it 63 to immediately attempt to kill off all of its children. It may 64 take it several seconds to complete killing off its children. 65 Then the parent itself exits. Any requests in progress are 66 terminated, and no further requests are served.</p> 67 68 <h3>HUP Signal: restart now</h3> 69 70 <p>Sending the <code>HUP</code> signal to the parent causes it 71 to kill off its children like in <code>TERM</code> but the 72 parent doesn't exit. It re-reads its configuration files, and 73 re-opens any log files. Then it spawns a new set of children 74 and continues serving hits.</p> 75 76 <p>Users of the <a href="mod/mod_status.html">status module</a> 77 will notice that the server statistics are set to zero when a 78 <code>HUP</code> is sent.</p> 79 80 <p><strong>Note:</strong> If your configuration file has errors 81 in it when you issue a restart then your parent will not 82 restart, it will exit with an error. See below for a method of 83 avoiding this.</p> 84 85 <h3>USR1 Signal: graceful restart</h3> 86 87 <p><strong>Note:</strong> prior to release 1.2b9 this code is 88 quite unstable and shouldn't be used at all.</p> 89 90 <p>The <code>USR1</code> signal causes the parent process to 91 <em>advise</em> the children to exit after their current 92 request (or to exit immediately if they're not serving 93 anything). The parent re-reads its configuration files and 94 re-opens its log files. As each child dies off the parent 95 replaces it with a child from the new <em>generation</em> of 96 the configuration, which begins serving new requests 97 immediately.</p> 98 99 <p>This code is designed to always respect the <a 100 href="mod/core.html#maxclients">MaxClients</a>, <a 101 href="mod/core.html#minspareservers">MinSpareServers</a>, and 102 <a href="mod/core.html#maxspareservers">MaxSpareServers</a> 103 settings. Furthermore, it respects <a 104 href="mod/core.html#startservers">StartServers</a> in the 105 following manner: if after one second at least StartServers new 106 children have not been created, then create enough to pick up 107 the slack. This is to say that the code tries to maintain both 108 the number of children appropriate for the current load on the 109 server, and respect your wishes with the StartServers 110 parameter.</p> 111 112 <p>Users of the <a href="mod/mod_status.html">status module</a> 113 will notice that the server statistics are <strong>not</strong> 114 set to zero when a <code>USR1</code> is sent. The code was 115 written to both minimize the time in which the server is unable 116 to serve new requests (they will be queued up by the operating 117 system, so they're not lost in any event) and to respect your 118 tuning parameters. In order to do this it has to keep the 119 <em>scoreboard</em> used to keep track of all children across 120 generations.</p> 121 122 <p>The status module will also use a <code>G</code> to indicate 123 those children which are still serving requests started before 124 the graceful restart was given.</p> 125 126 <p>At present there is no way for a log rotation script using 127 <code>USR1</code> to know for certain that all children writing 128 the pre-restart log have finished. We suggest that you use a 129 suitable delay after sending the <code>USR1</code> signal 130 before you do anything with the old log. For example if most of 131 your hits take less than 10 minutes to complete for users on 132 low bandwidth links then you could wait 15 minutes before doing 133 anything with the old log.</p> 134 135 <p><strong>Note:</strong> If your configuration file has errors 136 in it when you issue a restart then your parent will not 137 restart, it will exit with an error. In the case of graceful 138 restarts it will also leave children running when it exits. 139 (These are the children which are "gracefully exiting" by 140 handling their last request.) This will cause problems if you 141 attempt to restart the server -- it will not be able to bind to 142 its listening ports. Before doing a restart, you can check the 143 syntax of the configuration files with the <code>-t</code> 144 command line argument (see <a 145 href="programs/httpd.html">httpd</a> ). This still will not 146 guarantee that the server will restart correctly. To check the 147 semantics of the configuration files as well as the syntax, you 148 can try starting httpd as a non-root user. If there are no 149 errors it will attempt to open its sockets and logs and fail 150 because it's not root (or because the currently running httpd 151 already has those ports bound). If it fails for any other 152 reason then it's probably a config file error and the error 153 should be fixed before issuing the graceful restart.</p> 154 155 <h3>Appendix: signals and race conditions</h3> 156 157 <p>Prior to Apache 1.2b9 there were several <em>race 158 conditions</em> involving the restart and die signals (a simple 159 description of race condition is: a time-sensitive problem, as 160 in if something happens at just the wrong time it won't behave 161 as expected). For those architectures that have the "right" 162 feature set we have eliminated as many as we can. But it should 163 be noted that there still do exist race conditions on certain 164 architectures.</p> 165 166 <p>Architectures that use an on disk <a 167 href="mod/core.html#scoreboardfile">ScoreBoardFile</a> have the 168 potential to corrupt their scoreboards. This can result in the 169 "bind: Address already in use" (after <code>HUP</code>) or 170 "long lost child came home!" (after <code>USR1</code>). The 171 former is a fatal error, while the latter just causes the 172 server to lose a scoreboard slot. So it might be advisable to 173 use graceful restarts, with an occasional hard restart. These 174 problems are very difficult to work around, but fortunately 175 most architectures do not require a scoreboard file. See the <a 176 href="mod/core.html#scoreboardfile">ScoreBoardFile</a> 177 documentation for a architecture uses it.</p> 178 179 <p><code>NEXT</code> and <code>MACHTEN</code> (68k only) have 180 small race conditions which can cause a restart/die signal to 181 be lost, but should not cause the server to do anything 182 otherwise problematic. 183 <!-- they don't have sigaction, or we're not using it -djg --> 184 </p> 185 186 <p>All architectures have a small race condition in each child 187 involving the second and subsequent requests on a persistent 188 HTTP connection (KeepAlive). It may exit after reading the 189 request line but before reading any of the request headers. 190 There is a fix that was discovered too late to make 1.2. In 191 theory this isn't an issue because the KeepAlive client has to 192 expect these events because of network latencies and server 193 timeouts. In practice it doesn't seem to affect anything either 194 -- in a test case the server was restarted twenty times per 195 second and clients successfully browsed the site without 196 getting broken images or empty documents. 197 <hr /> 198 199 <h3 align="CENTER">Apache HTTP Server</h3> 200 <a href="./"><img src="images/index.gif" alt="Index" /></a> 201 202 </p> 203 </body> 204</html> 205 206 207 208
