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);

DESCRIPTION

getgroups()
    Up to size supplementary group IDs (of the calling process) 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 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, -1 is returned, and errno is set appropriately.

setgroups()
    On success, zero is returned. On error, -1 is returned, and errno is set 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 than the number of supplementary group IDs, but is not zero.

EPERM
    The calling process has insufficient privilege to call setgroups().

NOTES
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):
    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 _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 SVr3), X/OPEN, 4.3BSD. The getgroups() function is in POSIX.1. Since setgroups() requires privilege, it is not covered by POSIX.1.

SEE ALSO
getgid(2), setgid(2), initgroups(3), capabilities(7)