real and effective group IDs
The real and effective group IDs of the current process are set according to the
arguments. The saved group ID will be set to the new value of the real group
ID if a real group ID is specified and either the new real group ID value is
different from the current value or the new value of the effective group ID
differs from the current saved group ID.
Unprivileged users may change either group ID to the current value of the real,
effective, or saved group ID. Only the superuser may make other changes.
Supplying a value of -1 for either the real or effective group ID forces the
system to substitute the current ID in place of the -1 parameter.
() function was intended to allow
swapping the real and effective group IDs in set-group-ID programs to
temporarily relinquish the set-group-ID value. This purpose is now better
served by the use of the
When setting the real and effective group IDs to the same value, the
function is preferred.
Upon successful completion, the value 0 is returned; otherwise the
value -1 is returned and the global variable
is set to indicate the error.
- The current process is not the superuser and a change other
than changing the effective group ID to the real group ID was
() function conforms to the
IEEE Std 1003.1-2008
specification, except that the conditions for
changing the saved group ID differ and that, if it is changed, the saved group
ID is set to the real group ID instead of the effective group ID.
() system call first appeared in
, predating POSIX. A semantically different
version appeared in 4.4BSD
. The current version, with
the original semantics restored, appeared in OpenBSD