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From: mwm@eris.BERKELEY.EDU (Mike (No one lives forever.) Meyer)
Newsgroups: comp.unix.questions,comp.unix.wizards
Subject: Groups in 4BSD (Was: System V letting random users chown)
Message-ID: <2837@jade.BERKELEY.EDU>
Date: Tue, 17-Mar-87 20:14:23 EST
Article-I.D.: jade.2837
Posted: Tue Mar 17 20:14:23 1987
Date-Received: Thu, 19-Mar-87 07:23:05 EST
References: <713@aw.sei.cmu.edu.sei.cmu.edu> <15054@sun.uucp> <2454@mtgzy.UUCP> <15136@sun.uucp>
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Reply-To: mwm@eris.BERKELEY.EDU (Mike (No one lives forever.) Meyer)
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In article <15136@sun.uucp> guy%gorodish@Sun.COM (Guy Harris) writes:
>How it works:
>	When you log in, your effective group ID is set to the number
>	in the group field of your "/etc/passwd" entry.  Your group
>	set is initialized from { group ID in "/etc/passwd" } (union)
>	<set of groups in "/etc/group" that you belong to> (although

Not quite, Guy. I think it's just confusing terminolgy, though.

Your effective group id is set from the group field in /etc/passwd.

Your group set is the set of groups your in /etc/group, EXCEPT for the
group that is your group id. The operation is set difference, not
union.

In addition, if you use the setregid system call to set your real
group id to a group that's in your group set, it will be taken from
your group set. A second setregid back to the original group id will
not put things back, so that the group will have vanished from your
group set.

The semantics of the gid/group set aren't very clean. If you're going
to be writing code that dynamically deals with either one, be
carefull, or you'll surprise yourself.

Finally, notice that Guy's limit of 16 users is 4.3BSD. It was 8 in
4.2.

	<mike

--
But I'll survive, no you won't catch me,		Mike Meyer
I'll resist the urge that is tempting me,		ucbvax!mwm
I'll avert my eyes, keep you off my knee,		mwm@berkeley.edu
But it feels so good when you talk to me.		mwm@ucbjade.BITNET