GETGROUPLIST
Section: Linux Programmer's Manual (3)
Updated: 2017-09-15
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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);
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
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().
VERSIONS
This function is present since glibc 2.2.4.
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).
| Interface | Attribute | Value
|
|
getgrouplist()
| Thread safety | MT-Safe locale
|
CONFORMING TO
This function is nonstandard; it appears on most BSDs.
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);
}
SEE ALSO
getgroups(2),
setgroups(2),
getgrent(3),
group_member(3),
group(5),
passwd(5)
COLOPHON
This page is part of release 4.13 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/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- VERSIONS
-
- ATTRIBUTES
-
- CONFORMING TO
-
- BUGS
-
- EXAMPLE
-
- Program source
-
- SEE ALSO
-
- COLOPHON
-
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