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From: guy@gorodish.UUCP
Newsgroups: comp.unix.questions
Subject: Re: Groups in 4BSD (Was: System V letting random users chown)
Message-ID: <15529@sun.uucp>
Date: Tue, 24-Mar-87 14:19:55 EST
Article-I.D.: sun.15529
Posted: Tue Mar 24 14:19:55 1987
Date-Received: Thu, 26-Mar-87 04:31:46 EST
References: <2454@mtgzy.UUCP> <2940005@hpisod2.HP.COM> <2242@ptsfa.UUCP>
Sender: news@sun.uucp
Reply-To: guy@sun.UUCP (Guy Harris)
Organization: Sun Microsystems, Mountain View
Lines: 21

>>Nothing is wrong with it until you decide that you want to access files
>>belonging to two different groups in the same process.  BSD has a list
>>of groups for each process.
>
>/etc/group in SysV does the same thing.

No, it doesn't.  "/etc/group" in systems that haven't picked up the
4.2BSD "group set" notion merely indicates which people can "newgrp"
to a particular group.  A process can only have one group that it
belongs to.  If you want to access a file that's only accessible to
members of a particular group, and you're not currently running with
that as your group ID, you have to "newgrp" to that group.

In systems that have picked up the 4.2BSD "group set" notion, "login"
adds the first N (for some value of N, ~8 on 4.2BSD, ~16 on 4.3BSD)
groups that a user is listed as a member of to the "group set" for
that user's login shell process.  (It uses "/etc/group" for this, of
course; the file has the same format that it does in other UNIX
systems.)  That process, and its descendants (unless they change
their effective group ID or group set), can access files accessible
to any of those groups.