GETGROUPS(2) Linux Programmer's Manual GETGROUPS(2)
NAME
getgroups, setgroups - get/set(7,n,1 builtins) 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);
DESCRIPTION
getgroups
Up to size supplementary group IDs (of the calling process) are
returned in(1,8) list. It is unspecified whether the effective group
ID of the calling process is included in(1,8) 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 modi-
fied, but the total number of supplementary group IDs for the
process is returned.
setgroups
Sets the supplementary group IDs for the process. Appropriate
privileges (Linux: the CAP_SETGID capability) are required.
RETURN VALUE
getgroups
On success, the number of supplementary group IDs is returned.
On error(8,n), -1 is returned, and errno is set(7,n,1 builtins) appropriately.
setgroups
On success, zero is returned. On error(8,n), -1 is returned, and
errno is set(7,n,1 builtins) appropriately.
ERRORS
EFAULT list has an invalid address.
EINVAL For setgroups, size is greater than NGROUPS (32 for Linux
2.0.32). For getgroups, size is less(1,3) than the number of supple-
mentary group IDs, but is not zero.
EPERM The calling process has insufficient privilege to call set-
groups.
NOTES
A process can have up to at least NGROUPS_MAX supplementary group IDs
in(1,8) addition to the effective group ID. The set(7,n,1 builtins) of supplementary group
IDs is inherited from the parent process and may be changed using set-
groups. The maximum number of supplementary group IDs can be found
using sysconf(3):
long ngroups_max;
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(3,n) _BSD_SOURCE is defined
(either explicitly, or implicitly, by not defining _POSIX_SOURCE or
compiling with the -ansi flag).
CONFORMING TO
SVr4, SVID (issue 4 only; these calls were not present in(1,8) SVr3),
X/OPEN, 4.3BSD. The getgroups function is in(1,8) POSIX.1. Since setgroups
requires privilege, it is not covered by POSIX.1.
SEE ALSO
getgid(2), setgid(2), initgroups(3), capabilities(7)
Linux 2.6.6 2004-05-27 GETGROUPS(2)