GETGROUPLIST(3) | Linux Programmer's Manual | GETGROUPLIST(3) |
NAME
getgrouplist - get list of groups to which a user belongsSYNOPSIS
#include <grp.h>Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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.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.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 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(5), passwd(5)COLOPHON
This page is part of release 3.53 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/.2008-07-03 | GNU |