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GETGROUPS(2) Linux Programmer's Manual GETGROUPS(2)
NAME
getgroups, setgroups - get/set list of supplementary group IDs
SYNOPSIS
#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
DESCRIPTION
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 supple-
mentary 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.
RETURN VALUE
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.
ERRORS
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.
CONFORMING TO
SVr4, 4.3BSD. The getgroups() function is in POSIX.1-2001. Since set-
groups() requires privilege, it is not covered by POSIX.1-2001.
NOTES
A process can have up to NGROUPS_MAX supplementary group IDs in addi-
tion to the effective group ID. The constant NGROUPS_MAX is defined in
<limits.h>. 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 at run time
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. Since Linux 2.6.4, the maximum number of supplemen-
tary group IDs is also exposed via the Linux-specific read-only file,
/proc/sys/kernel/ngroups_max.
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.
SEE ALSO
getgid(2), setgid(2), getgrouplist(3), initgroups(3), capabilities(7),
credentials(7)
COLOPHON
This page is part of release 3.69 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
http://www.kernel.org/doc/man-pages/.
Linux 2013-10-18 GETGROUPS(2)
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