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<title>s6: the s6-ipcserverd program</title>
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<h1> The <tt>s6-ipcserverd</tt> program </h1>
<p>
<tt>s6-ipcserverd</tt> is the serving part of the
<a href="s6-ipcserver.html">s6-ipcserver</a> super-server.
It assumes that its stdin is a bound and listening Unix
domain socket, and
it accepts connections from clients connecting to it, forking a
program to handle each connection.
</p>
<h2> Interface </h2>
<pre>
s6-ipcserverd [ -1 ] [ -v verbosity ] [ -P | -p ] [ -c <em>maxconn</em> ] [ -C <em>localmaxconn</em> ] <em>prog...</em>
</pre>
<ul>
<li> s6-ipcserverd accepts connections from clients to an already
bound and listening SOCK_STREAM Unix domain socket which is its
standard input. </li>
<li> For every client connection to this socket, it
forks. The child sets some environment variables, then
executes <em>prog...</em> with stdin reading from the socket and
stdout writing to it. </li>
<li> Depending on the verbosity level, it logs what it does to stderr. </li>
<li> It runs until killed by a signal. Depending on the received
signal, it may kill its children before exiting. </li>
</ul>
<h2> Environment variables </h2>
<p>
For each connection, an instance of <em>prog...</em> is spawned with
the following variables set:
</p>
<ul>
<li> PROTO: always set to IPC </li>
<li> IPCREMOTEEUID: set to the effective UID of the client,
unless credentials lookups have been disabled </li>
<li> IPCREMOTEEGID: set to the effective GID of the client,
unless credentials lookups have been disabled </li>
<li> IPCREMOTEPATH: set to the path associated with the remote socket,
if any. Be aware that it may contain arbitrary characters. </li>
<li> IPCCONNNUM: set to the number of connections originating from
the same user (i.e. same uid) </li>
</ul>
<p>
If client credentials lookup has been disabled, IPCREMOTEEUID and
IPCREMOTEEGID will be set, but empty.
</p>
<h2> Options </h2>
<ul>
<li> <tt>-1</tt> : write a newline to stdout, and close stdout,
right before entering the client-accepting loop.
If stdout is suitably redirected, this can be used by monitoring
programs to check when the server is accepting connections. See
<a href="notifywhenup.html">this page</a> for more information on
readiness notification. </li>
<li> <tt>-v <em>verbosity</em></tt> : be more or less
verbose. <em>verbosity</em> can be 0 (quiet), 1 (normal), or 2
(verbose). </li>
<li> <tt>-P</tt> : disable client credentials lookups. The
IPCREMOTEEUID and IPCREMOTEEGID environment variables will be unset
in every instance of <em>prog...</em>. This is the portable option,
because not every system supports credential lookup across Unix domain
sockets; but it is not as secure. </li>
<li> <tt>-p</tt> : enable client credentials lookups. This
is the default; it works at least on Linux, Solaris, and
*BSD systems. On systems that do not support it, every connection
attempt will fail with a warning message. </li>
<li> <tt>-c <em>maxconn</em></tt> : accept at most
<em>maxconn</em> concurrent connections. Default is 40. It is
impossible to set it higher than 1000. </li>
<li> <tt>-C <em>localmaxconn</em></tt> : accept at most
<em>localmaxconn</em> connections from the same user ID.
Default is 40. It is impossible to set it higher than <em>maxconn</em>. </li>
</ul>
<h2> Signals </h2>
<ul>
<li> SIGTERM: exit. </li>
<li> SIGHUP: send a SIGTERM and a SIGCONT to all children. </li>
<li> SIGQUIT: send a SIGTERM and a SIGCONT to all children, then exit. </li>
<li> SIGABRT: send a SIGKILL to all children, then exit. </li>
</ul>
<h2> Notes </h2>
<ul>
<li> Unlike his close cousin
<a href="http://www.superscript.com/ucspi-ipc/ipcserver.html">ipcserver</a>,
s6-ipcserverd does not perform operations such as access control. Those are
delegated to the
<a href="s6-ipcserver-access.html">s6-ipcserver-access</a> program. </li>
<li> s6-ipcserverd can be used to set up
<a href="localservice.html">local services</a>. </li>
<li> s6-ipcserverd is meant to be execve'd into by a program that gets
the listening socket. That program is normally
<a href="s6-ipcserver-socketbinder.html">s6-ipcserver-socketbinder</a>,
which creates the socket itself; but it can be a different one if the
socket is to be retrieved by another means, for instance by fd-passing
from a fd-holding daemon (some people call this "socket activation"). </li>
</ul>
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