GETGROUPLIST(3) Linux Programmer's Manual GETGROUPLIST(3)
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(): _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 getgrou-
plist(); 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 getgrou-
plist() 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.
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 speci-
fies 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 3.74 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
http://www.kernel.org/doc/man-pages/.
GNU 2014-08-19 GETGROUPLIST(3)
Czas wygenerowania: 0.00015 sek.
Created with the man page lookup class by Andrew Collington.
Based on a C man page viewer by Vadim Pavlov
Unicode soft-hyphen fix (as used by RedHat) by Dan Edwards
Some optimisations by Eli Argon
Caching idea and code contribution by James Richardson
Copyright © 2003-2023 Linux.pl
Hosted by Hosting Linux.pl