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From: aglew%mycroft@gswd-vms.arpa (Andy Glew)
Newsgroups: comp.unix.wizards
Subject: Groups in 4BSD
Message-ID: <5035@brl-adm.ARPA>
Date: Thu, 19-Mar-87 11:35:04 EST
Article-I.D.: brl-adm.5035
Posted: Thu Mar 19 11:35:04 1987
Date-Received: Sat, 21-Mar-87 04:36:15 EST
Sender: news@brl-adm.ARPA
Lines: 34

...> Groups in 4BSD

    In a previous post someone said <<4.2 BSD's group system makes
    System V style chown'ing by non-root unnecessary - newgrp isn't
    necessary in BSD>>. To which I made the rather cryptic comment
    <<Only 16 groups.  Newgrp isn't necessary. Really?>>

I apologize for being cryptic. What I meant to say was that BSD does
have the equivalent of newgrp - it's just not accessible to the user.
As is obviously necessary when you could possibly be a member of an 
>NGROUPS groups. So I reject "newgrp isn't necessary". Newgrp isn't
AS necessary, but it's still occasionally necessary.

16 is too small a number. There should be a way to dynamically add groups
to your group set, with some sort of replacement algorithm. I don't 
accept "static during your terminal session"; effectively, it's globally
static, unless you allow people to do their own editing of /etc/groups,
if only to reorder the list of groups and determine which subset of
the greater than 16 groups they belong to are installed as their groupset.

Of course, there is a way - setgroups(2), with setgid(2) for the first
function, changing the default gid for file creation. Unfortunately,
setgroups is a super-user call.

So there is a need for newgrp - although it's provided as a system call,
not a "standard" command. This breaks the rule "anything you can do in C
should have a command level interface".

Obviously, the command level interface for setgroups would be a setuid 
program that checked whether the groups that the user is requesting 
be added (set) into his active groupset are permitted to him.

Andy "Krazy" Glew. Gould CSD-Urbana.    USEnet:  ihnp4!uiucdcs!ccvaxa!aglew
1101 E. University, Urbana, IL 61801    ARPAnet: aglew@gswd-vms.arpa