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<title>s6: the s6-fghack program</title>
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<meta name="Keywords" content="s6 command s6-fghack foreground program background hack anti-backgrounding tool" />
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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>
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<h1> The s6-fghack program </h1>
<p>
s6-fghack is an anti-backgrounding tool.
</p>
<h2> Interface </h2>
<pre>
s6-fghack <em>prog...</em>
</pre>
<ul>
<li> s6-fghack opens a lot of file descriptors (all writing to a single pipe). </li>
<li> Then it forks and executes <em>prog...</em>. </li>
<li> If something gets written on one of those descriptors, it's a bug in <em>prog</em>.
s6-fghack then complains and exits 102. </li>
<li> Unless <em>prog...</em> goes out of its way to close descriptors it does know about,
s6-fghack is able to detect when <em>prog...</em> exits. It exits with the same exit
code (or 111 if <em>prog...</em> has crashed). </li>
</ul>
<h2> Notes </h2>
<p>
s6-fghack is what it says: a hack. Ideally, you should never have to use it.
It is only useful when you want to supervise a daemon that does not provide a
"stay in the foreground" option; and even then, the right thing is to report
this as a bug to the daemon author and have it fixed.
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