NETGROUP(5) BSD File Formats Manual NETGROUP(5)NAMEnetgroup — defines network groups
The netgroup file specifies ``netgroups'', which are sets of (host, user,
domain) tuples that are to be given similar network access.
Each line in the file consists of a netgroup name followed by a list of
the members of the netgroup. Each member can be either the name of
another netgroup or a specification of a tuple as follows:
(host, user, domain)
where the host, user, and domain are character string names for the cor‐
responding component. Any of the comma separated fields may be empty to
specify a ``wildcard'' value or may consist of the string ``-'' to spec‐
ify ``no valid value''. The members of the list may be separated by
whitespace and/or commas; the ``\'' character may be used at the end of a
line to specify line continuation. Lines are limited to 1024 characters.
The functions specified in getnetgrent(3) should normally be used to
access the netgroup database.
Lines that begin with a # are treated as comments.
On most other platforms, netgroups are only used in conjunction with NIS
and local /etc/netgroup files are ignored. With FreeBSD, netgroups can
be used with either NIS or local files, but there are certain caveats to
consider. The existing netgroup system is extremely inefficient where
innetgr(3) lookups are concerned since netgroup memberships are computed
on the fly. By contrast, the NIS netgroup database consists of three
separate maps (netgroup, netgroup.byuser and netgroup.byhost) that are
keyed to allow innetgr(3) lookups to be done quickly. The FreeBSD
netgroup system can interact with the NIS netgroup maps in the following
· If the /etc/netgroup file does not exist, or it exists and is
empty, or it exists and contains only a ‘+’, and NIS is run‐
ning, netgroup lookups will be done exclusively through NIS,
with innetgr(3) taking advantage of the netgroup.byuser and
netgroup.byhost maps to speed up searches. (This is more or
less compatible with the behavior of SunOS and similar plat‐
· If the /etc/netgroup exists and contains only local netgroup
information (with no NIS ‘+’ token), then only the local
netgroup information will be processed (and NIS will be
· If /etc/netgroup exists and contains both local netgroup data
and the NIS ‘+’ token, the local data and the NIS netgroup map
will be processed as a single combined netgroup database.
While this configuration is the most flexible, it is also the
least efficient: in particular, innetgr(3) lookups will be
especially slow if the database is large.
/etc/netgroup the netgroup database
The file format is compatible with that of various vendors, however it
appears that not all vendors use an identical format.
SEE ALSOgetnetgrent(3), exports(5)BUGS
The interpretation of access restrictions based on the member tuples of a
netgroup is left up to the various network applications. Also, it is not
obvious how the domain specification applies to the BSD environment.
The netgroup database should be stored in the form of a hashed db(3)
database just like the passwd(5) database to speed up reverse lookups.
BSD December 11, 1993 BSD