real and effective user IDs
The real and effective user IDs of the current process are set according to the
arguments. The saved user ID will be set to the new value of the real user ID
if a real user ID is specified and either the new real user ID value is
different from the current value or the new value of the effective user ID
differs from the current saved user ID.
Unprivileged users may change either user ID to the current value of the real,
effective, or saved user ID. Only the superuser may make other changes.
Supplying a value of -1 for either the real or effective user 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 user IDs in set-user-ID programs to
temporarily relinquish the set-user-ID value. This purpose is now better
served by the use of the
When setting the real and effective user 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 user ID to the real user ID was
() function conforms to the
IEEE Std 1003.1-2008
specification, except that the conditions for
changing the saved user ID differ and that, if it is changed, the saved user
ID is set to the real user ID instead of the effective user 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