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<title>prepare-svscan</title>
<meta name="Description" content="Helper script to initialize a supervision tree." />
<meta name="Keywords" content="goetia s6 s6-rc supervision tree" />
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<header>
<p>
<a href="//0x53.net/software/goetia/goetia-base">goetia-base</a>
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<a href="//0x53.net/software/goetia">goetia</a>
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<a href="//0x53.net/software">Software</a>
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<h1>The prepare-svscan program</h1>
<p>
prepare-svscan does generic preparation of the
<a href="//0x53.net/software/goetia/supervisiontree.html">supervision tree</a>.
It is also used in system-init and
<a href="./user-init.html">user-init</a>.
</p>
<h2>Interface</h2>
<pre> prepare-svscan <em>workingdir</em> <em>rundir</em> <em>bundle</em> <em>prog...</em></pre>
<ul>
<li>
prepare-svscan sets its standard input to <code>/dev/null</code>.
</li>
<li>
It sets the umask to <code>0022</code>.
</li>
<li>
It creates the directory <code><em>rundir</em></code>.
</li>
<li>
It copies all contents of <code><em>workingdir</em>/run-image/.</code>
to <code><em>rundir</em>/</code>.
</li>
<li>
It changes its standard output to <code><em>rundir</em>/service/s6-svscan-log/fifo</code>.
</li>
<li>
prepare-svscan then forks a background process that:
<ul>
<li>
waits for a reading end at <code><em>rundir</em>/service/s6-svscan-log/fifo</code>.
</li>
<li>
Once the above is given, if <code><em>rundir</em>/s6-rc</code> does <em>not</em> exist,
</li>
<li>
it initiates <a href="https://skarnet.org/software/s6-rc/">s6-rc</a> on
<code><em>rundir</em>/service</code> using
<a href="https://skarnet.org/software/s6-rc/s6-rc-init.html">s6-rc-init</a>
and starts the bundle <code><em>bundle</em></code> using s6-rc.
</li>
</ul>
</li>
<li>
It copies stderr to stdout.
</li>
<li>
If available, the directory <code><em>workingdir</em>/env</code> is sourced using
<a href="https://skarnet.org/software/s6/s6-envdir.html">s6-env</a>.
</li>
<li>
prepare-svscan executest into <code><em>prog...</em></code>,
which is usually directly or indirectly
<a href="https://skarnet.org/software/s6/s6-svscan.html">s6-svscan</a>.
</li>
</ul>
<p>
Once s6-svscan is launched it will start an
<a href="https://skarnet.org/software/s6/s6-supervise.html">s6-supervise</a>
process on <code><em>rundir</em>/service/s6-svscan-log</code> which starts
<a href="https://skarnet.org/software/s6/s6-log.html">s6-log</a> reading
from <code><em>rundir</em>/service/s6-svscan-log/fifo</code>.
This in turn triggers the forked background process to continue with its second step.
</p>
<h2>Exit codes</h2>
<ul>
<li>
prepare-svscan usually executes into
<a href="https://skarnet.org/software/s6/s6-svscan.html">s6-svscan</a>
which exits according to its page.
</li>
<li>
Since prepare-svscan is an
<a href="https://skarnet.org/software/execline/">execline</a>
script, it exits with an approximation
of employed program that failed.
</li>
<li>
prepare-svscan mostly uses
<a href="https://skarnet.org/software/execline/">execline</a>
and
<a href="https://skarnet.org/software/s6/">s6</a>
software, the exit behaviour of which can be looked up on
their respective pages.
</li>
<li>
See also:
<a href="https://skarnet.org/software/execline/exitcodes.html">execline exit code handling</a>.
</li>
</ul>
<h2>Options</h2>
<ul>
<li>
There are no otions to prepare-svscan.
</li>
</ul>
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