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 getgrouplist(); 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 com-
       plete 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 specifies 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(5), passwd(5)

COLOPHON
       This page is part of release 3.25 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)