The netgroup is a SunOS invention. A netgroup database is a list of
string triples (hostname,username,domainname) or other
netgroup names. Any of the elements in a triple can be empty, which means that
anything matches. The functions described here allow access to the netgroup
databases. The file /etc/nsswitch.conf defines what database is
The setnetgrent() call defines the netgroup that will be searched by
subsequent getnetgrent() calls. The getnetgrent() function
retrieves the next netgroup entry, and returns pointers in host,
user, domain. A NULL pointer means that the corresponding entry
matches any string. The pointers are valid only as long as there is no call to
other netgroup related functions. To avoid this problem you can use the GNU
function getnetgrent_r() that stores the strings in the supplied
buffer. To free all allocated buffers use endnetgrent().
In most cases you only want to check if the triplet
(hostname,username,domainname) is a member of a netgroup.
The function innetgr() can be used for this without calling the above
three functions. Again, a NULL pointer is a wildcard and matches any string.
The function is thread-safe.