SETREGID(2) BSD System Calls Manual SETREGID(2)
setregid -- set real and effective group IDs
setregid(gid_t rgid, gid_t egid);
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
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.
The setregid() 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 setegid(2) function.
When setting the real and effective group IDs to the same value, the
setgid(2) function is preferred.
Upon successful completion, the value 0 is returned; otherwise the
value -1 is returned and the global variable errno is set to indicate the
[EPERM] The current process is not the superuser and a change
other than changing the effective group ID to the real
group ID was specified.
getgid(2), setegid(2), setgid(2), setresgid(2), setreuid(2)
The setregid() function conforms to the IEEE Std 1003.1-2008
(``POSIX.1'') 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.
The setregid() system call first appeared in 4.1cBSD, predating POSIX. A
semantically different version appeared in 4.4BSD. The current version,
with the original semantics restored, appeared in OpenBSD 3.3.
BSD February 5, 2015 BSD