GETNETGRENT(3C) Standard C Library Functions GETNETGRENT(3C)


getnetgrent, getnetgrent_r, setnetgrent, endnetgrent, innetgr - get
network group entry


#include <netdb.h>

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 endnetgrent(void);

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(5)).

These functions consult the source specified for netgroup in the
/etc/nsswitch.conf file (see nsswitch.conf(5)).

The function innetgr() returns 1 if there is a netgroup netgroup that
contains the specified machine, user, domain triple as a member;
otherwise 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
multithreaded applications.

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 members
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 caller.
This implementation is not safe for use in multi-threaded applications.

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 specified 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
performed 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. Calling
setnetgrent() resets the enumeration position for all threads. If
multiple threads interleave calls to getnetgrent_r() each will enumerate
a disjoint subset of the netgroup. Thus the effective use of these
functions in multi-threaded applications may require coordination by the


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(7) for descriptions of the following attributes:

|MT-Level | See DESCRIPTION section. |


Intro(2), Intro(3), netgroup(5), nsswitch.conf(5), attributes(7)


The function getnetgrent_r() is included in this release on an
uncommitted basis only, and is subject to change or removal in future
minor releases.


Network groups are usually stored in network information services, such
as LDAP, or NIS, but may alternatively be stored in the local
/etc/netgroup file. The netgroup line of the nsswitch.conf(5) file
determines which of those sources are used.

When compiling multi-threaded applications, see Intro(3), Notes On
Multithread Applications, for information about the use of the _REENTRANT

February 25, 2017 GETNETGRENT(3C)