| NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON | The Linux Programming Interface |
GETGROUPS(2) Linux Programmer's Manual GETGROUPS(2)
getgroups, setgroups - get/set list of supplementary group IDs
#include <sys/types.h>
#include <unistd.h>
int getgroups(int size, gid_t list[]);
#include <grp.h>
int setgroups(size_t size, const gid_t *list);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
setgroups(): _BSD_SOURCE
getgroups() returns the supplementary group IDs of the calling process in
list. The argument size should be set to the maximum number of items that can
be stored in the buffer pointed to by list. If the calling process is a
member of more than size supplementary groups, then an error results. It is
unspecified whether the effective group ID of the calling process is included
in the returned list. (Thus, an application should also call getegid(2) and
add or remove the resulting value.)
If size is zero, list is not modified, but the total number of supplementary
group IDs for the process is returned. This allows the caller to determine
the size of a dynamically allocated list to be used in a further call to
getgroups().
setgroups() sets the supplementary group IDs for the calling process.
Appropriate privileges (Linux: the CAP_SETGID capability) are required. The
size argument specifies the number of supplementary group IDs in the buffer
pointed to by list.
On success, getgroups() returns the number of supplementary group IDs. On
error, -1 is returned, and errno is set appropriately.
On success, setgroups() returns 0. On error, -1 is returned, and errno is set
appropriately.
EFAULT list has an invalid address.
getgroups() can additionally fail with the following error:
EINVAL size is less than the number of supplementary group IDs, but is not
zero.
setgroups() can additionally fail with the following errors:
EINVAL size is greater than NGROUPS_MAX (32 before Linux 2.6.4; 65536 since
Linux 2.6.4).
ENOMEM Out of memory.
EPERM The calling process has insufficient privilege.
SVr4, 4.3BSD. The getgroups() function is in POSIX.1-2001. Since setgroups()
requires privilege, it is not covered by POSIX.1-2001.
A process can have up to NGROUPS_MAX supplementary group IDs in addition to
the effective group ID. The set of supplementary group IDs is inherited from
the parent process, and preserved across an execve(2).
The maximum number of supplementary group IDs can be found using sysconf(3):
long ngroups_max;
ngroups_max = sysconf(_SC_NGROUPS_MAX);
The maximum return value of getgroups() cannot be larger than one more than
this value.
The original Linux getgroups() system call supported only 16-bit group IDs.
Subsequently, Linux 2.4 added getgroups32(), supporting 32-bit IDs. The glibc
getgroups() wrapper function transparently deals with the variation across
kernel versions.
getgid(2), setgid(2), getgrouplist(3), initgroups(3), capabilities(7),
credentials(7)
This page is part of release 3.32 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/.
Linux 2010-11-22 GETGROUPS(2)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface