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

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

NAME         top

       getgrouplist - get list of groups to which a user belongs

SYNOPSIS         top

       #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():
           Since glibc 2.19:
               _DEFAULT_SOURCE
           Glibc 2.19 and earlier:
               _BSD_SOURCE

DESCRIPTION         top

       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         top

       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         top

       This function is present since glibc 2.2.4.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see
       attributes(7).

       ┌───────────────┬───────────────┬────────────────┐
       │Interface      Attribute     Value          │
       ├───────────────┼───────────────┼────────────────┤
       │getgrouplist() │ Thread safety │ MT-Safe locale │
       └───────────────┴───────────────┴────────────────┘

CONFORMING TO         top

       This function is nonstandard; it appears on most BSDs.

BUGS         top

       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         top

       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         top

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

COLOPHON         top

       This page is part of release 4.08 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
       https://www.kernel.org/doc/man-pages/.

GNU                              2016-03-15                  GETGROUPLIST(3)