GETGROUPLIST(3)

NAME
getgrouplist - list of groups a user belongs to

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 for all the groups user belongs to. Up to *ngroups group IDs corresponding to these groups are stored in the array groups; the return value from the function is the number of group IDs actually stored. The group group is automatically included in the list of groups returned by getgrouplist().

RETURN VALUE
If *ngroups is smaller than the total number of groups found, then getgrouplist() returns -1. In all cases the actual number of groups is stored in *ngroups.

VERSIONS
This function is present since glibc 2.2.4.

CONFORMING TO
This function is non-standard; it appears on most BSDs.

BUGS
The glibc 2.3.2 implementation of this function is broken: it overwrites memory when the actual number of groups is larger than *ngroups.

EXAMPLE
/* This crashes with glibc 2.3.2 */
#include <stdio.h>
#include <stdlib.h>
#include <grp.h>
#include <pwd.h>

int
main(void)
{
    int i, ng = 0;
    char *user = "who";       /* username here */
    gid_t *groups = NULL;
    struct passwd *pw = getpwnam(user);

    if (pw == NULL)
        exit(EXIT_SUCCESS);

    if (getgrouplist(user, pw->pw_gid, NULL, &ng) < 0) {
        groups = (gid_t *) malloc(ng * sizeof (gid_t));
        getgrouplist(user, pw->pw_gid, groups, &ng);
    }

    for (i = 0; i < ng; i++)
        printf("%d\n", groups[i]);

    exit(EXIT_SUCCESS);
}

SEE ALSO
getgroups(2), setgroups(2)

COLOPHON
This page is part of release 2.76 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/.