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getgrouplist

NAME

getgrouplist - list of groups a user belongs to

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 for all the groups user belongs to. Up to *ngroups group IDs corresponding to these groups are stored in the array groups; the return value from the function is the number of group IDs actually stored. The group group is automatically included in the list of groups returned by getgrouplist().

RETURN VALUE

If *ngroups is smaller than the total number of groups found, then getgrouplist() returns -1. In all cases the actual number of groups is stored in *ngroups.

VERSIONS

This function is present since glibc 2.2.4.

CONFORMING TO

This function is non-standard; it appears on most BSDs.

BUGS

The glibc 2.3.2 implementation of this function is broken: it overwrites memory when the actual number of groups is larger than *ngroups.

EXAMPLE

 /* This crashes with glibc 2.3.2 */
 #include <stdio.h>
 #include <stdlib.h>
 #include <grp.h>
 #include <pwd.h>
 
 int
 main(void)
 {
     int i, ng = 0;
     char *user = "who";       /* username here */
     gid_t *groups = NULL;
     struct passwd *pw = getpwnam(user);
 
     if (pw == NULL)
         exit(EXIT_SUCCESS);
 
     if (getgrouplist(user, pw->pw_gid, NULL, &ng) < 0) {
         groups = (gid_t *) malloc(ng * sizeof (gid_t));
         getgrouplist(user, pw->pw_gid, groups, &ng);
     }
 
     for (i = 0; i < ng; i++)
         printf("%d\n", groups[i]);
 
     exit(EXIT_SUCCESS);
 }
 

SEE ALSO

getgroups(2), setgroups(2)