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<title>s6: the s6-permafailon program</title>
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<p>
<a href="index.html">s6</a><br />
<a href="//skarnet.org/software/">Software</a><br />
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<h1> The <tt>s6-permafailon</tt> program </h1>
<p>
<tt>s6-permafailon</tt> is a program that is meant to be used
in the <tt>./finish</tt> script of a
<a href="servicedir.html">service directory</a> supervised by
<a href="s6-supervise.html">s6-supervise</a>. When used, it
reads and analyses the death tally of a service (i.e. the recent
process death events that happened), and if the death tally
matches a given pattern, it causes <em>permanent failure</em>
of the service, i.e. it tells the supervisor not to try and
restart it.
</p>
<h2> Interface </h2>
<pre>
s6-permafailon <em>secs</em> <em>deathcount</em> <em>events</em> <em>prog...</em>
</pre>
<ul>
<li> <tt>s6-permafailon</tt> must have the service directory of the
tested service as its current directory. This is the default if it is
called from the <tt>finish</tt> script of the service. </li>
<li> It reads the <em>death tally</em> of the service, which is
maintained by <a href="s6-supervise.html">s6-supervise</a>. </li>
<li> If the supervised process has died at least <em>deathcount</em>
times in the last <em>secs</em> seconds with a cause listed in
<em>events</em>, then <tt>s6-permafailon</tt> exits 125. </li>
<li> Else <tt>s6-permafailon</tt> execs into <em>prog...</em>. </li>
</ul>
<p>
<em>events</em> is a comma-separated list of events. An event can be
one of the following:
</p>
<ul>
<li> An exit code, which is an integer between 0 and 255. Example: <tt>1</tt> </li>
<li> An exit code interval, which is two exit codes separated by a dash. Example: <tt>1-50</tt> </li>
<li> A signal name, or a signal number preceded by "SIG". Examples: <tt>SIGTERM</tt>, <tt>sigabrt</tt>, <tt>sig11</tt> </li>
</ul>
<h2> Usage </h2>
<ul>
<li> <a href="s6-supervise.html">s6-supervise</a> detects when the <tt>./finish</tt>
script of its service exits 125, and stops respawning the service. So, if the
<tt>./finish</tt> script is a chain-loading command line starting with a
<tt>s6-permafailon</tt> invocation (or containing such an invocation), when
<tt>s6-permafailon</tt> exits 125, then the <tt>./finish</tt> script also
exits 125 (because it is the same process), and the service is then marked as
failing permanently. </li>
<li> The <tt>./finish</tt> script is <em>naturally</em> a chain-loading
command line if it is written in the
<a href="//skarnet.org/software/execline/">execline</a> language. It
can also be made into a chain-loading command line from a shell script by using
<tt>exec s6-permafailon secs deathcount events rest-of-chainloading-cmdline...</tt> </li>
<li> Multiple invocations of <tt>s6-permafailon</tt> can be chained, in order
to test several death patterns. </li>
<li> If a permanent failure is triggered and <em>secs</em> is high, it is
possible that when the administrator manually launches the service again,
the next death triggers a permanent failure again. If this is not wanted,
the administrator should clear the death tally with the
<a href="s6-svdt-clear.html">s6-svdt-clear</a> command. </li>
<li> The current death tally can be viewed via the <a href="s6-svdt.html">s6-svdt</a>
command. </li>
</ul>
<h2> Example </h2>
<p>
<tt>s6-permafailon 60 5 1,101-103,SIGSEGV,SIGBUS <em>prog...</em></tt>
will exit 125 if the service has died 5 times in the last 60 seconds with
an exit code of 1, 101, 102 or 103, a SIGSEGV or a SIGBUS. Else it will
chainload into the <em>prog...</em> command line.
</p>
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