nsss
Software
skarnet.org

The nsss library interface

General information

libnsss is a client library meant to be used by client programs needing utmp functionality. It interacts with various server-side daemons such as nsssd-unix.

Application programs can use it directly, but most existing programs simply use the standard pwd.h, grp.h or shadow.h interfaces, which in nsss are implemented as a series of thin wrappers around the nsss library.

Compiling

• Make sure the nsss headers, as well as the skalibs headers, are visible in your header search path.
• Use #include <nsss/nsss.h>
• To use the standard pwd.h interface, you can just #include <pwd.h>, which will work as long as the nsss/pwd.h header is accessible in your header search path.
• Same thing for grp.h and shadow.h.

Linking

• Make sure the nsss library, as well as the skalibs library, are visible in your library search path.
• Link against -lnsss, -lskarnet,
`cat $SYSDEPS/socket.lib` and `cat $SYSDEPS/tainnow.lib`, $SYSDEPS being your skalibs sysdeps directory.

Programming

The nsss/nsss.h header is actually a collection of headers:

• nsss/nsss-unix.h implements basic access to the /etc/passwd, /etc/group and /etc/shadow database.
• nsss/nsss-switch.h implements connection via a Unix domain socket to a listening nsssd daemon, implementing an authentication backend based on what implementation of the daemon is listening.
• nsss/nsss-all.h implements a safe policy: first a connection via nsss-switch is attempted, and if no daemon is listening, the safe nsss-unix backend is used.

By default, the getpwnam() et al. functions are aliased to their nsss-all implementations. You can disable the nsss-unix fallback by compiling with the NSSS_DISABLE_UNIX macro defined (-DNSSS_DISABLE_UNIX). Or you can disable any attempt to connect to a daemon by compiling with the NSSS_DISABLE_SWITCH macro defined (-DNSSS_DISABLE_SWITCH).

(To be completed.)