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<title>nsss - a secure NSS-like implementation for small libcs</title>
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<p>
<a href="//skarnet.org/software/">Software</a><br />
<a href="//skarnet.org/">skarnet.org</a>
</p>
<h1> nsss </h1>
<h2> What is it ? </h2>
<p>
nsss is an implementation of a subset of the <tt>pwd.h</tt>,
<tt>group.h</tt> and <tt>shadow.h</tt> family of functions,
performing user database access on Unix systems.
</p>
<p>
Usually, user database access via <tt>getpwnam()</tt> and similar
function is provided by the system's libc. However, not all libcs implement
a configurable backend for the user/group database. For instance the
<a href="https://musl-libc.org/">musl</a> libc, on Linux, only supports
the standard <tt>/etc/passwd</tt> mechanism; it also supports the
<tt>nscd</tt> protocol but this is not quite enough:
<p>
<ul>
<li> musl only connects to nscd when it cannot find an answer in
its files backend </li>
<li> The nscd protocol does not support enumeration, so primitives
such as <tt>getpwent()</tt> cannot be implemented over nscd. </li>
</ul>
<p>
The mechanism used by glibc, called <tt>Name Service Switch</tt>
(abbreviated to <tt>nsswitch</tt> or <tt>NSS</tt>), has its own
<a href="nsswitch.html">set of issues</a> that makes it unsuitable
in certain situations.
</p>
<p>
<tt>nsss</tt> is a secure implementation of a "name service switch":
configurable user/group/shadow database access, providing <tt>getpwnam()</tt>
et al. functionality by communicating over a Unix domain socket with a daemon;
the daemon can perform lookups in any database it chooses.
</p>
<p>
<tt>nsss</tt> does not perform dynamic module
loading, only adds a small footprint to the application's binary,
and does not add any complex decision engine into the client's address
space. Applications can be statically linked against the <tt>nsss</tt>
library, and still benefit from configurable user database access
functions.
</p>
<hr />
<ul>
<li> <a href="nsswitch.html">The problem with <tt>nsswitch</tt></a> </li>
<li> <a href="overview.html">An overview of <tt>nsss</tt></a> </li>
</ul>
<hr />
<h2> Installation </h2>
<h3> Requirements </h3>
<ul>
<li> A POSIX-compliant system with a standard C development environment </li>
<li> GNU make, version 3.81 or later </li>
<li> <a href="//skarnet.org/software/skalibs/">skalibs</a> version
2.9.1.0 or later. It's a build-time requirement. It's also a run-time
requirement if you link against the shared version of the skalibs
library. </li>
<li> <a href="//skarnet.org/software/s6/">s6</a> version
2.9.0.1 or later. It's a <em>run-time</em> requirement only, to run
the nsssd service (and can be done without if you have a suitable replacement
for <a href="//skarnet.org/software/s6/s6-ipcserver">s6-ipcserver</a>). </li>
</ul>
<h3> Licensing </h3>
<p>
nsss is free software. It is available under the
<a href="http://opensource.org/licenses/ISC">ISC license</a>.
</p>
<h3> Download </h3>
<ul>
<li> The current released version of nsss is <a href="nsss-0.0.2.1.tar.gz">0.0.2.1</a>. </li>
<li> Alternatively, you can checkout a copy of the
<a href="//git.skarnet.org/cgi-bin/cgit.cgi/nsss/">nsss
git repository</a>:
<pre> git clone git://git.skarnet.org/nsss </pre> </li>
<li> There's also a
<a href="https://github.com/skarnet/nsss">GitHub mirror</a>
of the nsss git repository. </li>
</ul>
<h3> Compilation </h3>
<ul>
<li> See the enclosed INSTALL file for installation details. </li>
</ul>
<h3> Upgrade notes </h3>
<ul>
<li> <a href="upgrade.html">This page</a> lists the differences to be aware of between
the previous versions of nsss and the current one. </li>
</ul>
<hr />
<h2> Reference </h2>
<h3> Commands </h3>
<p>
The following commands are not meant to be directly invoked on the
command-line. They are meant to be used behind a Unix domain socket
super-server such as
<a href="https://skarnet.org/software/s6/s6-ipcserver.html">s6-ipcserver</a>
in order to provide a
<a href="https://skarnet.org/software/s6/localservice.html">local service</a>.
Depending on the chosen command, the service will provide a different
backend to the name service.
</p>
<ul>
<li> The <a href="nsssd-unix.html"><tt>nsssd-unix</tt></a> program </li>
<li> The <a href="nsssd-nslcd.html"><tt>nsssd-nslcd</tt></a> program </li>
</ul>
<p>
Future versions of nsss will come with more backends.
</p>
<h3> Libraries </h3>
<ul>
<li> <a href="libnsss/">The <tt>nsss</tt> library interface</a>,
which applications use. A client application using one of the
following primitives will automatically perform libnsss calls:
<ul>
<li> endpwent() </li>
<li> setpwent() </li>
<li> getpwent() </li>
<li> getpwent_r() </li>
<li> getpwuid() </li>
<li> getpwuid_r() </li>
<li> getpwnam() </li>
<li> getpwnam_r() </li>
<li> endgrent() </li>
<li> setgrent() </li>
<li> getgrent() </li>
<li> getgrent_r() </li>
<li> getgrgid() </li>
<li> getgrgid_r() </li>
<li> getgrnam() </li>
<li> getgrnam_r() </li>
<li> getgrouplist() </li>
<li> endspent() </li>
<li> setspent() </li>
<li> getspent() </li>
<li> getspent_r() </li>
<li> getspnam() </li>
<li> getspnam_r() </li>
</ul> </li>
<li> <a href="libnsssd/">The <tt>nsssd</tt> library interface</a>,
which can be used to write additional backends. </li>
</ul>
<hr />
<a name="related">
<h2> Related resources </h2>
</a>
<h3> nsss discussion </h3>
<ul>
<li> <tt>nsss</tt> is discussed on the
<a href="//skarnet.org/lists.html#skaware">skaware</a> mailing-list. </li>
</ul>
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