getnetgrent, getnetgrent_r, setnetgrent, endnetgrent, innetgr - get
network group entry
int getnetgrent(char **machinep, char **userp, char **domainp);
int getnetgrent_r(char **machinep, char **userp, char **domainp,
char *buffer, intbuflen);
int setnetgrent(const char *netgroup);
int innetgr(const char *netgroup, const char *machine,
const char *user, const char *domain);
These functions are used to test membership in and enumerate members of
``netgroup'' network groups defined in a system database. Netgroups
are sets of (machine,user,domain) triples (see netgroup(4)).
These functions consult the source specified for netgroup in the
/etc/nsswitch.conf file (see nsswitch.conf(4)).
The function innetgr() returns 1 if there is a netgroup netgroup that
contains the specified machine, user, domain triple as a member; other‐
wise it returns 0. Any of the supplied pointers machine, user, and
domain may be NULL, signifying a "wild card" that matches all values in
that position of the triple.
The innetgr() function is safe for use in single-threaded and multi‐
The functions setnetgrent(), getnetgrent(), and endnetgrent() are used
to enumerate the members of a given network group.
The function setnetgrent() establishes the network group specified in
the parameter netgroup as the current group whose members are to be
Successive calls to the function getnetgrent() will enumerate the mem‐
bers of the group established by calling setnetgrent(); each call
returns 1 if it succeeds in obtaining another member of the network
group, or 0 if there are no further members of the group.
When calling either getnetgrent() or getnetgrent_r(), addresses of the
three character pointers are used as arguments, for example:
char *mp, *up, *dp;
getnetgrent(&mp, &up, &dp);
Upon successful return from getnetgrent(), the pointer mp points to a
string containing the name of the machine part of the member triple, up
points to a string containing the user name and dp points to a string
containing the domain name. If the pointer returned for mp, up, or dp
is NULL, it signifies that the element of the netgroup contains wild
card specifier in that position of the triple.
The pointers returned by getnetgrent() point into a buffer allocated by
setnetgrent() that is reused by each call. This space is released when
an endnetgrent() call is made, and should not be released by the call‐
er. This implementation is not safe for use in multi-threaded applica‐
The function getnetgrent_r() is similar to getnetgrent() function, but
it uses a buffer supplied by the caller for the space needed to store
the results. The parameter buffer should be a pointer to a buffer
allocated by the caller and the length of this buffer should be speci‐
fied by the parameter buflen. The buffer must be large enough to hold
the data associated with the triple. The getnetgrent_r() function is
safe for use both in single-threaded and multi-threaded applications.
The function endnetgrent() frees the space allocated by the previous
setnetgrent() call. The equivalent of an endnetgrent() implicitly per‐
formed whenever a setnetgrent() call is made to a new network group.
Note that while setnetgrent() and endnetgrent() are safe for use in
multi-threaded applications, the effect of each is process-wide. Call‐
ing setnetgrent() resets the enumeration position for all threads. If
multiple threads interleave calls to getnetgrent_r() each will enumer‐
ate a disjoint subset of the netgroup. Thus the effective use of these
functions in multi-threaded applications may require coordination by
The function getnetgrent_r() will return 0 and set errno to ERANGE if
the length of the buffer supplied by caller is not large enough to
store the result. See Intro(2) for the proper usage and interpretation
of errno in multi-threaded applications.
The functions setnetgrent() and endnetgrent() return 0 upon success.
See attributes(5) for descriptions of the following attributes:
│ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
│MT-Level │ See DESCRIPTION section. │
SEE ALSOIntro(2), Intro(3), netgroup(4), nsswitch.conf(4), attributes(5)WARNINGS
The function getnetgrent_r() is included in this release on an uncom‐
mitted basis only, and is subject to change or removal in future minor
Only the Network Information Services, NIS and NIS+, are supported as
sources for the netgroup database.
When compiling multi-threaded applications, see Intro(3), Notes On
Multithread Applications, for information about the use of the _REEN‐
Apr 5, 2004 GETNETGRENT(3C)