getgroupmembership(3) [netbsd man page]

GETGROUPLIST(3) 					   BSD Library Functions Manual 					   GETGROUPLIST(3)

NAME

     getgrouplist, getgroupmembership, -- calculate group access list

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <unistd.h>

     int
     getgrouplist(const char *name, gid_t basegid, gid_t *groups, int *ngroups);

     int
     getgroupmembership(const char *name, gid_t basegid, gid_t *groups, int maxgrp, int *ngroups);

DESCRIPTION

     The getgrouplist() and getgroupmembership() functions read through the group database and calculate the group access list for the user speci-
     fied in name.  The basegid is automatically included in the groups list.  Typically this value is given as the group number from the password
     database.

     The resulting group list is returned in the integer array pointed to by groups.

     For getgrouplist(), the caller specifies the size of the groups array in the integer pointed to by ngroups.

     For getgroupmembership(), the caller specifies the size of the groups array in maxgrp.

     The actual number of groups found is returned in ngroups.

     Duplicate group ids will be suppressed from the result.

RETURN VALUES

     The getgrouplist() and getgroupmembership() functions return 0 if successful, and return -1 if the size of the group list is too small to
     hold all the user's groups.  In the latter case, the groups array will be filled with as many groups as will fit and ngroups will contain the
     total number of groups found.

FILES

     /etc/group  group membership list

SEE ALSO

     setgroups(2), initgroups(3), group(5)

HISTORY

     The getgrouplist() function first appeared in 4.4BSD.  The getgroupmembership() function first appeared in NetBSD 3.0 to address an API defi-
     ciency in getgrouplist().

BUGS

     The getgrouplist() function uses the routines based on getgrent(3).  If the invoking program uses any of these routines, the group structure
     will be overwritten in the call to getgrouplist().

BSD
								  January 6, 2005							       BSD

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 getgrouplist() 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>
", 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
",
		       ngroups);
	    exit(EXIT_FAILURE);
	   }

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

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

	   exit(EXIT_SUCCESS);
       }

SEE ALSO

       getgroups(2), setgroups(2), getgrent(3), group(5), passwd(5)

COLOPHON

       This  page is part of release 3.27 of the Linux man-pages project.  A description of the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

GNU
								    2008-07-03							   GETGROUPLIST(3)