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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | VERSIONS | ATTRIBUTES | CONFORMING TO | BUGS | EXAMPLES | SEE ALSO | COLOPHON |
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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():
Since glibc 2.19:
_DEFAULT_SOURCE
Glibc 2.19 and earlier:
_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.
For an explanation of the terms used in this section, see
attributes(7).
┌───────────────────────────────┬───────────────┬────────────────┐
│Interface │ Attribute │ Value │
├───────────────────────────────┼───────────────┼────────────────┤
│getgrouplist() │ Thread safety │ MT-Safe locale │
└───────────────────────────────┴───────────────┴────────────────┘
This function is nonstandard; 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)
Program source
#include <stdio.h>
#include <stdlib.h>
#include <grp.h>
#include <pwd.h>
int
main(int argc, char *argv[])
{
int ngroups;
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]);
gid_t *groups = malloc(sizeof(*groups) * ngroups);
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 (int 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_member(3),
group(5), passwd(5)
This page is part of release 5.13 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 2021-03-22 GETGROUPLIST(3)
Pages that refer to this page: capsh(1), getent(1), getgroups(2), getgrent(3), group_member(3), nsswitch.conf(5)
Copyright and license for this manual page
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