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<title>s6: the s6-fdholder-transferdump program</title>
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<h1> The <tt>s6-fdholder-transferdump</tt> program </h1>
<p>
<tt>s6-fdholder-transferdump</tt> connects to two separate
<a href="s6-fdholderd.html">fd-holding daemons</a> and
transfers the content of the first one to the second one.
</p>
<h2> Interface </h2>
<pre>
s6-fdholder-transferdump [ -t <em>timeoutfrom:timeoutto</em> ] <em>pathfrom</em> <em>pathto</em>
</pre>
<ul>
<li> <tt>s6-fdholder-transferdump</tt> connects to a
<a href="s6-fdholderd.html">s6-fdholderd</a> server process listening on
<em>pathfrom</em> and gets the whole set of file descriptors from
this server, with their identifiers and (when relevant) expiration
dates. </li>
<li> It then connects to a different instance of
<a href="s6-fdholderd.html">s6-fdholderd</a>, listening on <em>pathto</em>,
and stores the set of file descriptors to it. The set is
<em>added</em> to the second server, which keeps the descriptors
it was already holding. </li>
</ul>
<h2> Options </h2>
<ul>
<li> <tt>-t <em>timeoutfrom</em>:<em>timeoutto</em></tt> :
if the operations cannot be
processed in <em>timeoutfrom</em> (for the connection to <em>pathfrom</em>)
or <em>timeoutto</em> (for the connection to <em>pathto</em>) milliseconds,
then fail with an error message.
Communications with the servers should be near-instant, so this option is
only here to protect users against programming errors (connecting to the
wrong socket, for instance). </li>
</ul>
<h2> Exit codes </h2>
<ul>
<li> 0: success. </li>
<li> 1: the source server denied the operation. The meaning of the error messages
is explained <a href="s6-fdholder-errorcodes.html">here</a>. </li>
<li> 2: the destination server denied the operation. The meaning of the error messages
is explained <a href="s6-fdholder-errorcodes.html">here</a>. </li>
<li> 100: wrong usage. </li>
<li> 111: system call failed - that includes attempting to connect to a
nonexistent socket, or one where no <a href="s6-fdholderd.html">s6-fdholderd</a>
daemon is listening. </li>
</ul>
<h2> Notes </h2>
<ul>
<li> Dumping the entire state of <a href="s6-fdholderd.html">s6-fdholderd</a>
requires special authorizations. Make sure the s6-fdholderd instances are
<a href="s6-fdholderd.html#configuration">configured</a> to accept
dump-getting and dump-setting requests from your client. </li>
<li> A typical use case of
<a href="s6-fdholder-transferdump.html">s6-fdholder-transferdump</a> is
when the main fd-holding daemon needs to upgrade, or restart for some reason.
Transferring the file descriptors into another, temporary fd-holding daemon
instance allows it to restart without losing the descriptors. </li>
</ul>
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