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<!DOCTYPE html>
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<title>goetia-shutdown</title>
<meta name="Description" content="Shutdown service for FreeBSD providing the actual shutdown procedure." />
<meta name="Keywords" content="goetia s6 s6-rc service FreeBSD shutdown" />
</head>
<header>
<p>
<a href="//0x53.net/software/goetia/goetia-freebsd-init">goetia-freebsd-init</a>
<br />
<a href="//0x53.net/software/goetia">goetia</a>
<br />
<a href="//0x53.net/software">Software</a>
<br />
<a href="//0x53.net">0x53.net</a>
</p>
</header>
<body>
<h1>The goetia-shutdown service</h1>
<p>
goetia-shutdown is the service that starts
<a href="//0x53.net/software/goetia/goetia-base/bin/system-shutdown-daemon.html">system-shutdown-daemon</a>.
goetia-shutdown is down by default.
Starting it initiates the shutdown procedure.
</p>
<p>
goetia-shutdown consists of three scripts:
</p>
<h2>run</h2>
<ul>
<li>
This script just executes system-shutdown-daemon.
</li>
</ul>
<h2>stage3b</h2>
<ul>
<li>
stage3b tries to execute <code>./stage4</code>,
which is by default not executable.
If it can not execute <code>./stage4</code>,
and <em>only</em> in this case,
it continues with the following.
</li>
<li>
It makes <code>./stage4</code> executable.
</li>
<li>
It sends SIGCONT to all processes.
</li>
<li>
It sleeps for 1 second.
</li>
<li>
It writes a banner to its standard out.
</li>
<li>
It send SIGKILL to all processes.
</li>
<li>
This also stops the system-shutdown-daemon process.
It is automatically restarted by the system supervision tree,
but this time, <em>both</em> the files
<code>./stage3b</code> and
<code>./stage4</code>
are executable.
Which leads to the execution of <code>./stage4</code>.
</li>
</ul>
<h2>stage4</h2>
<ul>
<li>
stage4 reads the envdir at the
<code>shutdown-directive</code> subdirectory of the
<a href="//0x53.net/software/goetia/rundir.html#system">system runtimedirectory</a>
using
<a href="https://skarnet.org/software/s6/s6-envdir.html">s6-envdir</a>.
</li>
<li>
It reads the <code>DIRECTIVE</code> evironment variable,
defaulting to <code>-r</code>, if <code>DIRECTIVE</code> is
not specified.
</li>
<li>
It runs <code>umount -A</code>.
</li>
<li>
It remounts the root filesystem read-only.
</li>
<li>
It runs <code>shutdown -o ${DIRECTIVE} now</code>.
</li>
</ul>
<h2>Notes</h2>
<p>
The entire shutdown procedure roughly works as follows:
</p>
<ul>
<li>
This service, running
<a href="//0x53.net/software/goetia/goetia-base/bin/system-shutdown-daemon.html">system-shutdown-daemon</a>
gets the instructions from
<a href="//0x53.net/software/goetia/goetia-freebsd-init/bin/system-shutdown.html">system-shutdown</a>
to shutdown.
</li>
<li>
system-shutdown-daemon does most of the shutdown procedure.
Part of it is to make stage3b executable.
In the end, system-shutdown-daemon sends SIGTERM to all processes but
PID 1, including itself.
</li>
<li>
this service gets restarted automatically.
system-shutdown-daemon now instantly executes into stage3b.
</li>
<li>
stage3b makes stage4 executable.
Followed by sending SIGKILL to all processes
but PID 1, including itself.
</li>
<li>
The final restart of this service causes
system-shutdown-daemon to instantly execute into
stage3b which instantly executes into stage4,
which instructs the Kernel to do the actual
halt, poweroff or reboot.
</li>
</ul>
</body>
</html>
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