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<title>s6: the s6-svc program</title>
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<p>
<a href="index.html">s6</a><br />
<a href="http://skarnet.org/software/">Software</a><br />
<a href="http://skarnet.org/">skarnet.org</a>
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<h1> The s6-svc program </h1>
<p>
s6-svc sends commands to a running <a href="s6-supervise.html">s6-supervise</a>
process. In other words, it's used to control a supervised process; among
other benefits, it allows an administrator to send signals to daemons without
knowing their PIDs, and without using horrible hacks such as .pid files.
</p>
<h2> Interface </h2>
<pre>
s6-svc [ -D | -U ] [ -t <em>timeout</em> ] [ -abqhkti12pcoduxO ] <em>servicedir</em>
</pre>
<p>
s6-svc sends the given series of commands to the
<a href="s6-supervise.html">s6-supervise</a> process monitoring the
<em>servicedir</em> directory, then exits 0. It exits 111 if it cannot send
a command, or 100 if no s6-supervise process is running on <em>servicedir</em>.
</p>
<h2> Options </h2>
<ul>
<li> <tt>-a</tt> : send a SIGALRM to the supervised process </li>
<li> <tt>-b</tt> : send a SIGABRT to the supervised process </li>
<li> <tt>-q</tt> : send a SIGQUIT to the supervised process </li>
<li> <tt>-h</tt> : send a SIGHUP to the supervised process </li>
<li> <tt>-k</tt> : send a SIGKILL to the supervised process </li>
<li> <tt>-t</tt> : send a SIGTERM to the supervised process </li>
<li> <tt>-i</tt> : send a SIGINT to the supervised process </li>
<li> <tt>-1</tt> : send a SIGUSR1 to the supervised process </li>
<li> <tt>-2</tt> : send a SIGUSR2 to the supervised process </li>
<li> <tt>-p</tt> : send a SIGSTOP to the supervised process </li>
<li> <tt>-c</tt> : send a SIGCONT to the supervised process </li>
<li> <tt>-o</tt> : once. Equivalent to "-uO". </li>
<li> <tt>-d</tt> : down. If the supervised process is up, send it
a SIGTERM and a SIGCONT. Do not restart it. </li>
<li> <tt>-u</tt> : up. If the supervised process is down, start it.
Automatically restart it when it dies. </li>
<li> <tt>-x</tt> : exit. When the service is asked to be down and
the supervised process dies, s6-supervise will exit too. This command should
normally never be used on a working system. </li>
<li> <tt>-O</tt> : Once at most. Do not restart the supervised process
when it dies. If it is down when the command is received, do not even start
it. </li>
<li> <tt>-t <em>timeout</em></tt> : if the <tt>-D</tt> or
<tt>-U</tt> option has been given, <tt>-t</tt> specifies a timeout
(in milliseconds) after which s6-svc will exit 1 with an error message if
the service still hasn't reached the desired state. By default, the
timeout is 0, which means that s6-svc will block indefinitely. </li>
<li> <tt>-D</tt> : s6-svc will not exit until the service is down. </li>
<li> <tt>-U</tt> : s6-svc will not exit until the service is up and
<a href="notifywhenup.html">ready</a> as notified by the daemon itself.
Be careful to only use this command on services that send readiness
notifications and are managed by <a href="s6-notifywhenup.html">s6-notifywhenup</a>,
else the command will never be successful. </li>
</ul>
<h2> Usage examples </h2>
<pre> s6-svc -h /service/httpd </pre>
<p>
Send a SIGHUP to the process represented by the <tt>/service/httpd</tt>
service directory. Traditionally, this makes web servers reload their
configuration file.
</p>
<pre> s6-svc -t /service/sshd </pre>
<p>
Kill (and automatically restart, if the wanted state of the service is up)
the process represented by the <tt>/service/sshd</tt> service directory -
typically the sshd server.
</p>
<pre> s6-svc -Dd /service/ftpd </pre>
<p>
Take down the ftpd server and block until the process is really down.
</p>
<pre> s6-svc -Uu -t 5000 /service/ftpd </pre>
<p>
Bring up the ftpd server and block until it has sent notification that it
is ready. Exit 1 if it is still not ready after 5 seconds.
</p>
<pre> s6-svc -a /service/httpd/log </pre>
<p>
Send a SIGALRM to the logger process for the httpd server. If this logger
process is <a href="s6-log.html">s6-log</a>, this triggers a log rotation.
</p>
<h2> Internals </h2>
<ul>
<li> s6-svc writes control commands into the <tt><em>servicedir</em>/supervise/control</tt>
FIFO. A s6-supervise process running on <em>servicedir</em> will be listening to this FIFO,
and will read and interpret those commands. </li>
<li> When invoked with the <tt>-D</tt> or <tt>-U</tt> option, s6-svc executes into
<a href="s6-svlisten1.html">s6-svlisten1</a>, which will listen to service state
changes and spawn another s6-svc instance (without the <tt>-D</tt> or <tt>-U</tt>
option) that will send the commands to the service. Any error message written during
the waiting period will mention it is being written by s6-svlisten1; this is normal. </li>
</ul>
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