NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | VERSIONS | CONFORMING TO | BUGS | EXAMPLE | SEE ALSO | COLOPHON
GETGROUPLIST(3) Linux Programmer's Manual GETGROUPLIST(3)
getgrouplist - get list of groups to which a user belongs
#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
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.
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().
This function is present since glibc 2.2.4.
This function is non-standard; it appears on most BSDs.
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.
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)
#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);
}
getgroups(2), setgroups(2), getgrent(3), group(5), passwd(5)
This page is part of release 3.08 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)