#include <sys/types.h>

setregid(rgid, egid)

gid_t rgid, egid;
 DESCRIPTION
The real and effective group ID's of the current process
are set to the arguments.
Unprivileged users may change the real group
ID to the effective group ID and vice-versa; only the super-user 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.
 "RETURN VALUE
Upon successful completion, a value of 0 is returned. Otherwise,
a value of -1 is returned and errno is set to indicate the error.
 "ERRORS
 15
[EPERM]
The current process is not the super-user and a change
other than changing the effective group-id to the real group-id
was specified.
 "SEE ALSO"
getgid(2), setreuid(2), setgid(3)