UNIX groups (/etc/group)

[jeffrey w percival]

A while ago I posted a request about groups in UNIX, and received no
information, so I'd like to try again.  I can see why lumping several
users into a group so they can take advantage of group permissions is
useful, but I don't understand why there are groups (and users) such
as "bin" and "sys".  Names like these came on our 2.9BSD distribution
tape.  Can anybody tell me why "bin" and "sys" exist as users and groups,
why, for example, "sys" belongs to group "bin" and vice-versa?  what
is the "correct" usage of these entries in /etc/passwd and /etc/group?

I'd really appreciate even just a short note on this subject.  Thanks.

-- 
	Jeff Percival ...!uwvax!uwmacc!jwp