Manpage of GETGROUPLIST

GETGROUPLIST

Section: Linux Programmer's Manual (3)
Updated: 2016-03-15
Index
 

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 userbelongs to. Up to *ngroupsof these groups are returned in the array groups.

If it was not among the groups defined for userin the group database, then groupis 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 ngroupsargument 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 useris a member is less than or equal to *ngroups, then the value *ngroupsis returned.

If the user is a member of more than *ngroupsgroups, then getgrouplist() returns -1. In this case, the value returned in *ngroupscan 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).
InterfaceAttributeValue
getgrouplist() Thread safetyMT-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 userin 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 ngroupsvalue to be supplied to getgrouplist(). The following shell session shows examples of the use of this program:

$ ./a.out cecilia 0getgrouplist() returned -1; ngroups = 3
$ ./a.out cecilia 3ngroups = 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)


 

Index

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
VERSIONS
ATTRIBUTES
CONFORMING TO
BUGS
EXAMPLE
Program source
SEE ALSO

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