union of effective & real permissions

[utzoo!decvax!ucbvax!unix-wizards]

>From chico!esquire!psl at Berkeley Wed Sep  9 22:13:49 1981
UUCP and other programs which need to restrict their own priveleges can,
of course use setuid() or setgid() to do so.  This, however, only works
if either the real uid is root, (or if it needs to become the effective uid,
in which case having it setuid was probably a waste of time).  A further
complication is the question of the "right to kill".  Do both the real and
effective uids have the right to kill the process?  There are problems with
either answer to this question...