GETGROUPS(2) Linux Programmer's Manual GETGROUPS(2)
getgroups, setgroups - get/set list of supplementary group IDs
int getgroups(int size, gid_t list);
int setgroups(size_t size, const gid_t *list);
Up to size supplementary group IDs are returned in list. 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 supplemen-
tary group IDs for the process is returned.
Sets the supplementary group IDs for the process. Only the super-user may use this
On success, the number of supplementary group IDs is returned. On error, -1 is
returned, and errno is set appropriately.
On success, zero is returned. On error, -1 is returned, and errno is set appropri-
EFAULT list has an invalid address.
EPERM For setgroups, the user is not the super-user.
EINVAL For setgroups, size is greater than NGROUPS (32 for Linux 2.0.32). For getgroups,
size is less than the number of supplementary group IDs, but is not zero.
A process can have up to at least 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 may be changed using setgroups. The maximum number of supplementary group IDs
can be found using sysconf(3):
ngroups_max = sysconf(_SC_NGROUPS_MAX);
The maximal return value of getgroups cannot be larger than one more than the value
obtained this way.
The prototype for setgroups is only available if _BSD_SOURCE is defined (either explic-
itly, or implicitly, by not defining _POSIX_SOURCE or compiling with the -ansi flag).
SVr4, SVID (issue 4 only; these calls were not present in SVr3), X/OPEN, 4.3BSD. The get-
groups function is in POSIX.1. Since setgroups requires privilege, it is not covered by
initgroups(3), getgid(2), setgid(2)
Linux 2.0.32 1997-12-10 GETGROUPS(2)