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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ATTRIBUTES | STANDARDS | HISTORY | BUGS | EXAMPLES | SEE ALSO | COLOPHON |
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getgrouplist(3) Library Functions Manual getgrouplist(3)
getgrouplist - get list of groups to which a user belongs
Standard C library (libc, -lc)
#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
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.
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 to getgrouplist().
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────┬───────────────┬────────────────┐
│ Interface │ Attribute │ Value │
├──────────────────────────────┼───────────────┼────────────────┤
│ getgrouplist() │ Thread safety │ MT-Safe locale │
└──────────────────────────────┴───────────────┴────────────────┘
None.
glibc 2.2.4.
Before glibc 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.
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 <errno.h>
#include <grp.h>
#include <pwd.h>
#include <stdio.h>
#include <stdlib.h>
int
main(int argc, char *argv[])
{
int ngroups;
gid_t *groups;
struct group *gr;
struct passwd *pw;
if (argc != 3) {
fprintf(stderr, "Usage: %s <user> <ngroups>\n", argv[0]);
exit(EXIT_FAILURE);
}
ngroups = atoi(argv[2]);
groups = malloc(sizeof(*groups) * ngroups);
if (groups == NULL) {
perror("malloc");
exit(EXIT_FAILURE);
}
/* Fetch passwd structure (contains first group ID for user). */
errno = 0;
pw = getpwnam(argv[1]);
if (pw == NULL) {
if (errno)
perror("getpwnam");
else
fprintf(stderr, "no such user\n");
exit(EXIT_FAILURE);
}
/* 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 (int 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);
}
getgroups(2), setgroups(2), getgrent(3), group_member(3),
group(5), passwd(5)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.9.1.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2024-06-26. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.9.1 2024-06-15 getgrouplist(3)
Pages that refer to this page: capsh(1), getent(1), getgroups(2), getgrent(3), group_member(3), nsswitch.conf(5)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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