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<title>utmps: the utmps-utmpd program</title>
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<a href="index.html">utmps</a><br />
<a href="//skarnet.org/software/">Software</a><br />
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<h1> The utmps-utmpd program </h1>
<p>
utmps-utmpd manages the utmp database. It expects to be able to create, read and
modify a file named <tt>utmp</tt> in the directory it is launched in.
</p>
<p>
It is not meant to be called directly; instead, it is expected to be run from
a script as a part of a "utmpd"
<a href="//skarnet.org/software/s6/localservice.html">local service</a>.
</p>
<p>
The <tt>examples/</tt> subdirectory of the utmps package provides examples
on how to run such a service.
The simplest way to do so, for testing purposes, is a command line such as:
</p>
<pre>s6-ipcserver -l0 utmpd-socket utmps-utmpd</pre>
<p>
while being in the <tt>/run/utmps</tt> directory.
</p>
<p>
<tt>/run/utmps/.utmpd-socket</tt> is the default place where utmps's
implementation of the <tt>utmpx.h</tt> functions expects the utmpd
service to be. It can be changed at build time by giving the
<tt>--with-utmp-socket=PATH</tt> option to configure.
</p>
<p>
utmps-utmpd does not listen to the socket itself: it reads from its
standard input and writes to its standard output. It relies
on a superserver such as
<a href="//skarnet.org/software/s6/s6-ipcserver.html">s6-ipcserver</a>
to manage connections to the socket. An instance of utmps-utmpd is run
for every client connection;
every instance reads the effective uid of the client in an environment
variable set by the superserver, which allows it to filter operations -
for instance, it allows any user to read from the database but it only
allows root, and members of the group utmps-utmpd runs as, to write to it.
</p>
<p>
If more fine-grained authorizations are required (only allowing
certain users and groups to connect to the service), the superserver
can be configured to enforce them.
</p>
<p>
utmps-utmpd does not need to run as root, provided it can write its file;
it is recommended to create a <em>utmp</em> user and group, dedicated to
utmps-utmpd and
<a href="utmps-wtmpd.html">utmps-wtmpd</a> operation, and run the
superserver as this user and group.
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