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setregid -- set real and effective group ID
Standard C Library (libc, -lc)
setregid(gid_t rgid, gid_t egid);
The real and effective group ID's of the current process are set to the
arguments. If the real group ID is changed, the saved group ID is
changed to the new value of the effective group ID.
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 argument.
The setregid() system call 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 system call did not work correctly, and its
purpose is now better served by the use of the setegid(2) system call.
When setting the real and effective group IDs to the same value, the
standard setgid() system call is preferred.
The setregid() function returns the value 0 if successful; otherwise the
value -1 is returned and the global variable errno is set to indicate the
[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.
getgid(2), issetugid(2), setegid(2), setgid(2), setuid(2)
The setregid() system call appeared in 4.2BSD.