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); |
![[Note]](../stylesheet/note.png) |
Note | ||
|---|---|---|---|
|
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().
BUGS
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
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);
}
COLOPHON
This page is part of release 3.52 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/.
|
Copyright (C) 2008, Linux Foundation, written by Michael Kerrisk <mtk.manpagesgmail.com> A few pieces remain from an earlier version written in 2002 by Walter Harms (walter.harmsinformatik.uni-oldenburg.de) %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. %%%LICENSE_END |