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<p>
<a href="index.html">nsss</a><br />
<a href="//skarnet.org/software/">Software</a><br />
<a href="//skarnet.org/">skarnet.org</a>
</p>
<h1> An overview of nsss </h1>
<p>
nsss is a secure implementation of a subset of the
<tt>pwd.h</tt>, <tt>grp.h</tt> and <tt>shadow.h</tt> functionality, i.e.
user authentication on Unix systems. It includes full POSIX
functionality, a few GNU extensions, and an underlying
<a href="libnsss/">C client library</a> with better error reporting
than the POSIX interface specifies.
</p>
<p>
nsss has two parts: the client library and the nsssd service.
</p>
<h2> The nsss client library </h2>
<p>
The <a href="libnsss/">client library</a> provides:
</p>
<ul>
<li> <a href="libnsss/nsss-unix.html">nsss-unix</a>: a set of
functions providing access to the standard <tt>/etc/passwd</tt>,
<tt>/etc/group</tt> and <tt>/etc/shadow</tt> files. </li>
<li> <a href="libnsss/nsss-switch.html">nsss-switch</a>: a set of
functions implementing the same functionality as <tt>nsss-unix</tt>,
but instead of looking for information in the standard files, they
connect to a <em>nsssd service</em> (see below) that performs the
requests for them. </li>
<li> three implementations of the the standard <tt>getpwnam()</tt>
et al. functions: one using the <tt>nsss-unix</tt> functions, one
using the <tt>nsss-switch</tt> functions, and the default one, called
<tt>nsss-all</tt>, which attempts to connect to the nsssd service
and retrieve information from it, but falls back to the <tt>nsss-unix</tt>
implementation if it fails (for instance, if no nsssd service is
listening). </li>
</ul>
<p>
Applications wishing to use nsss should be built against this client
library. The <tt>getpwnam()</tt> et al. definitions will override those
of the libc, and use the <tt>nsss-all</tt>, <tt>nsss-switch</tt> or
<tt>nsss-unix</tt> depending on compilation options.
</p>
<p>
Unlike glibc's <tt>nsswitch</tt>, the nsss client library does not
use dynamically loadable modules. nsss can be statically linked, and
used in static programs. It's also quite light.
</p>
<h2> The nsssd service </h2>
<p>
For applications that need to use the <tt>nsss-all</tt> or
<tt>nsss-switch</tt> implementations of <tt>getpwnam()</tt> et al.
(and that is the point, otherwise the libc's implementation could
generally be used over <tt>nsss-unix</tt> instead!) there needs to
be a daemon running on the system, and serving requests from
<tt>nsss-switch</tt> clients.
</p>
<p>
That daemon should be set up by the system administrator. It should
listen to the <tt>/run/service/nsssd/s</tt> Unix domain socket; that
default location can be changed at nsss build time via the
<tt>--with-nsssd-socket</tt> option to the configure script.
</p>
<p>
As of 0.0.1.0, two suitable implementations of a nsssd daemon are
provided by the nsss package:
</p>
<ul>
<li> The <a href="nsssd-unix.html">nsssd-unix</a> program, which is
sort of a dummy implementation since it simply accesses the standard
files (it simply uses the <tt>nsss-unix</tt> library). It is still
useful for testing purposes, and to have a placeholder service that
can easily be replaced later. </li>
<li> The <a href="nsssd-nslcd.html">nsssd-nslcd</a> program, which
performs requests to a
<a href="https://arthurdejong.org/nss-pam-ldapd/nslcd.8">nslcd</a>
daemon running on the same system and returns the answers fetched
by nslcd. This allows nsss to get its users/groups information from
a LDAP database. </li>
</ul>
<p>
More implementations, with a wider variety of backends, will come
in future versions of nsss.
</p>
<p>
The provided programs are not meant to be run directly; instead, they
use the UCSPI protocol and must be spawned by a Unix domain super-server
(the equivalent of inetd, for Unix domain sockets). The
<a href="//skarnet.org/software/s6/s6-ipcserver.html">s6-ipcserver</a>
program, from the <a href="//skarnet.org/software/s6/">s6</a> package,
is such a super-server. What this means is that for instance, running the
following command-line as root will set up a correct nsss service:
</p>
<pre> s6-ipcserver -- /run/service/nsssd/s nsssd-unix </pre>
<p>
Refinements can be added to this command-line, such as options to
drop root privileges after binding to the socket, etc. Examples of how
to add a nsssd service to your init scripts are provided in the
<tt>examples/</tt> subdirectory of the nsss package, for OpenRC,
s6 or s6-rc based systems.
</p>
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