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<title>s6-linux-utils: the s6-uevent-spawner program</title>
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<a href="index.html">s6-linux-utils</a><br />
<a href="//skarnet.org/software/">Software</a><br />
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<h1> The <tt>s6-uevent-spawner</tt> program </h1>
<p>
<tt>s6-uevent-spawner</tt> listens to its standard input for
netlink-style events, and launches a helper program for every event,
similarly to what the hotplug interface does.
</p>
<p>
It is meant to be used together with
<a href="s6-uevent-listener.html">s6-uevent-listener</a>.
</p>
<h2> Interface </h2>
<pre>
s6-uevent-spawner [ -v <em>verbosity</em> ] [ -l <em>linevar</em> ] [ -t <em>l</em>:<em>t</em>:<em>k</em> ] <em>prog...</em>
</pre>
<ul>
<li> s6-uevent-spawner listens to its stdin for a series of strings
representing kernel uevents, as formatted by
<a href="s6-uevent-listener.html">s6-uevent-listener</a>. </li>
<li> For every event it reads, it spawns <em>prog...</em> with
the event variables added to the environment, just as if <em>prog...</em>
had been registered in <tt>/proc/sys/kernel/hotplug</tt>. However,
it reads the events sequentially, and waits for a <em>prog</em> instance
to finish before spawning another one. </li>
<li> When s6-uevent-spawner receives EOF: if an instance of
<em>prog</em> is alive, it first waits for it to die. Then it exits
0. </li>
</ul>
<h2> Options </h2>
<ul>
<li> <tt>-v</tt> <em>verbosity</em> : be more or less verbose.
Default verbosity is 1. 0 only prints fatal error messages. 3 is too much. </li>
<li> <tt>-l</tt> <em>linevar</em> : make the event description
(i.e. the first string in the netlink message announcing the event)
available in <em>prog</em> under the environment variable <em>linevar</em>.
By default, this first string is ignored - it is not needed, all the
event information is already in the other variables. </li>
<li> <tt>-t</tt> <em>l:t:k</em> : If <em>l</em>, <em>t</em> or <em>k</em> is
specified, they specify timeouts; by default, they are infinite.
If <em>prog...</em> is still alive after <em>l</em> milliseconds, s6-devd sends
it a SIGTERM. Then, if <em>prog...</em> is still alive after <em>t</em> more
milliseconds, s6-devd sends it a SIGKILL. Then, if <em>prog...</em> is still
alive after <em>k</em> more milliseconds, s6-uevent-spawner yells and exits 99. </li>
</ul>
<h2> Notes </h2>
<ul>
<li> The <em>prog...</em> helper should be very short-lived,
even if you are not using the <tt>-t</tt> option. Since helpers are
spawned sequentially, slow helpers can make events queue up and fill up
buffers. </li>
</ul>
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