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GETGROUPLIST(3)		   Linux Programmer's Manual	       GETGROUPLIST(3)

NAME
       getgrouplist - get list of groups to which a user belongs

SYNOPSIS
       #include	<grp.h>

       int getgrouplist(const char *user, gid_t	group,
			gid_t *groups, int *ngroups);

   Feature Test	Macro Requirements for glibc (see feature_test_macros(7)):

       getgrouplist(): _BSD_SOURCE

DESCRIPTION
       The  getgrouplist() function scans the group database (see group(5)) to
       obtain the list of groups that user belongs  to.	  Up  to  *ngroups  of
       these groups are	returned in the	array groups.

       If  it was not among the	groups defined for user	in the group database,
       then group is included in the  list  of	groups	returned  by  getgrou-
       plist();	 typically this	argument is specified as the group ID from the
       password	record for user.

       The ngroups argument is a value-result argument:	on  return  it	always
       contains	 the  number  of  groups found for user, including group; this
       value may be greater than the number of groups stored in	groups.

RETURN VALUE
       If the number of	groups of which	user is	a member is less than or equal
       to *ngroups, then the value *ngroups is returned.

       If  the	user  is  a member of more than	*ngroups groups, then getgrou-
       plist() returns -1.  In this case, the value returned in	 *ngroups  can
       be used to resize the buffer passed to a	further	call getgrouplist().

VERSIONS
       This function is	present	since glibc 2.2.4.

CONFORMING TO
       This function is	nonstandard; it	appears	on most	BSDs.

BUGS
       In  glibc  versions  before  2.3.3, the implementation of this function
       contains	a buffer-overrun bug: it returns the complete list  of	groups
       for  user  in  the array	groups,	even when the number of	groups exceeds
       *ngroups.

EXAMPLE
       The program below displays the group list for the  user	named  in  its
       first  command-line  argument.  The second command-line argument	speci-
       fies the	ngroups	value to be supplied to	getgrouplist().	 The following
       shell session shows examples of the use of this program:

	   $ ./a.out cecilia 0
	   getgrouplist() returned -1; ngroups = 3
	   $ ./a.out cecilia 3
	   ngroups = 3
	   16 (dialout)
	   33 (video)
	   100 (users)

   Program source

       #include	<stdio.h>
       #include	<stdlib.h>
       #include	<grp.h>
       #include	<pwd.h>

       int
       main(int	argc, char *argv[])
       {
	   int j, ngroups;
	   gid_t *groups;
	   struct passwd *pw;
	   struct group	*gr;

	   if (argc != 3) {
	       fprintf(stderr, "Usage: %s <user> <ngroups>\n", argv[0]);
	       exit(EXIT_FAILURE);
	   }

	   ngroups = atoi(argv[2]);

	   groups = malloc(ngroups * sizeof (gid_t));
	   if (groups == NULL) {
	       perror("malloc");
	       exit(EXIT_FAILURE);
	   }

	   /* Fetch passwd structure (contains first group ID for user)	*/

	   pw =	getpwnam(argv[1]);
	   if (pw == NULL) {
	       perror("getpwnam");
	       exit(EXIT_SUCCESS);
	   }

	   /* Retrieve group list */

	   if (getgrouplist(argv[1], pw->pw_gid, groups, &ngroups) == -1) {
	       fprintf(stderr, "getgrouplist() returned	-1; ngroups = %d\n",
		       ngroups);
	       exit(EXIT_FAILURE);
	   }

	   /* Display list of retrieved	groups,	along with group names */

	   fprintf(stderr, "ngroups = %d\n", ngroups);
	   for (j = 0; j < ngroups; j++) {
	       printf("%d", groups[j]);
	       gr = getgrgid(groups[j]);
	       if (gr != NULL)
		   printf(" (%s)", gr->gr_name);
	       printf("\n");
	   }

	   exit(EXIT_SUCCESS);
       }

SEE ALSO
       getgroups(2),  setgroups(2),  getgrent(3),  group_member(3),  group(5),
       passwd(5)

COLOPHON
       This page is part of release 3.74 of the	Linux  man-pages  project.   A
       description  of	the project, information about reporting bugs, and the
       latest	 version    of	  this	  page,	   can	   be	  found	    at
       http://www.kernel.org/doc/man-pages/.

GNU				  2014-08-19		       GETGROUPLIST(3)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | VERSIONS | CONFORMING TO | BUGS | EXAMPLE | SEE ALSO | COLOPHON

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