man pages section 3: Basic Library Functions

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Updated: July 2014
 
 

endnetgrent(3C)

Name

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

Synopsis

#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);

Description

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; 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 enumerated.

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 caller.

Errors

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.

Files

/etc/nsswitch.conf

Attributes

See attributes(5) for descriptions of the following attributes:

ATTRIBUTE TYPE
ATTRIBUTE VALUE
MT-Level
See DESCRIPTION section.

See Also

Intro(2), Intro(3), netgroup(4), nsswitch.conf(4), attributes(5)

Warnings

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.

Notes

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 _REENTRANT flag.