GETGROUPLIST

NAME

SYNOPSIS

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

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 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

CONFORMING TO

BUGS

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

COLOPHON