Mashey and crew basically did most of the original group work as part of PWB.   If you look at the Sixth Edition sources and the PWB 1.0 stuff, that is one of the places you will find differences.  With Seventh Edition (or I believe as part of the UNIX/TS work that Ken picked up), the Mashey group changes went back into the Research stream. With one of the predecessors to 4.2BSD (it may have 4.1A or 4.1B but frankly I have forgotten) Joy introduced the group scheme we all use today.

The Mashey scheme allowed an UID to be assigned to multiple groups, but only use (be in) a single group during the process lifetime.  IIRC the RJE system was based on it, but there were some other scripts that the PWB team needed. Check the original PWB docs, there is some explanation of them.  FWIW: new group was added to be similar to switch user (su), to change the gid when the setguid bit was not set on the file.   The truth is the early group stuff was not used by most admins.

With BSD and use of UNIX for large systems (particularly academic teaching systems), the desire to have some processes be in more than one group and be able to test the group file protections accordingly was desired -- for things like creating a group for each class - where the hand in system was write-only to the class's TA who was also part of the group.

I'm sure it was used in many other ways, but that was certainly one scheme we used at UCB when wnj added them.  Again check the 4.2 docs, where the BSD group scheme is explained.   This did seem useful and System V picked it up also fairly soon after BSD released it to the world, and fortunately did not change the BSD semantics.  

On Mon, Nov 15, 2021 at 11:12 AM Grant Taylor via COFF <> wrote:

Will someone please explain the history and usage of gpasswd / newgrp / sg?

I've run across them again recently while reading old Unix texts.  I've
been aware of them for years, but I've never actually used them for
anything beyond kicking the tires.  So I figured that I'd inquire of the
hive mind that is TUHS / COFF.

When was the concept of group passwords introduced?

What was the problem that group passwords were the solution for?

How common was the use of group passwords?

I ran into one comment indicating that they used newgrp to work around a
limitation in the number of (secondary) groups in relation to an NFS
implementation.  Specifically that the implementation of NFS they were
using didn't support more than 16 groups.  So they would switch their
primary group to work around this limit.

Does anyone have any interesting stories related to group passwords /
gpasswd / newgrp / sg?

Grant. . . .
unix || die

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