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<title>s6: the s6-svwait 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>
</p>
<h1> The s6-svwait program </h1>
<p>
s6-svwait blocks until a collection of supervised services goes up, or down.
</p>
<p>
s6-svwait only waits for notifications; it never polls.
</p>
<h2> Interface </h2>
<pre>
s6-svwait [ -U | -u | -d ] [ -a | -o ] [ -t <em>timeout</em> ] <em>servicedir...</em>
</pre>
<p>
s6-svwait monitors one or more <a href="servicedir.html">service
directories</a> given as its arguments, waiting for a state (ready, up or down) to
happen. It exits 0 when the wanted condition becomes true.
</p>
<h2> Options </h2>
<ul>
<li> <tt>-u</tt> : up. s6-svwait will wait until the services are up, as
reported by s6-supervise.
This is the default; it is not reliable, but it does not depend on specific
support in the service programs. See <a href="notifywhenup.html">this page</a>
for details. </li>
<li> <tt>-U</tt> : really up. s6-svwait will wait until the services are
up <em>and</em> ready as reported by the services themselves. This requires
specific support in the service programs, and the use of the
<tt>notification-fd</tt> file in the
<a href="servicedir.html">service directory</a>.
See the explanation on <a href="notifywhenup.html">this page</a>. </li>
<li> <tt>-d</tt> : down. s6-svwait will wait until the services are down. </li>
<li> <tt>-o</tt> : or. s6-svwait will wait until <em>one</em> of the
given services comes up or down. </li>
<li> <tt>-a</tt> : and. s6-svwait will wait until <em>all</em> of the
given services come up or down. This is the default. </li>
<li> <tt>-t <em>timeout</em></tt> : if the requested events have not
happened after <em>timeout</em> milliseconds, s6-svwait will print a message
to stderr and exit 1. By default, <em>timeout</em> is 0, which means no time
limit. </li>
</ul>
<h2> Notes </h2>
<ul>
<li> s6-svwait should be given one or more <em>service directories</em> as
arguments, not a <em>scan directory</em>. If you need to wait for a whole
scan directory, give all its contents as arguments to s6-svwait. </li>
<li> s6-svwait will only work on service directories that are already
active, i.e. have a <a href="s6-supervise.html">s6-supervise</a> process
running on them. It will not work on a service directory where
s6-supervise has not been started yet. </li>
</ul>
<h2> Internals </h2>
<p>
s6-svwait spawns a <a href="libs6/s6-ftrigrd.html">s6-ftrigrd</a> child to
listen to notifications sent by <a href="s6-supervise.html">s6-supervise</a>.
It also checks <tt>supervise/status</tt> files, as well as the
<tt>supervise/ready</tt> files if necessary, to get the current service
states, so it is immune to race conditions.
</p>
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