[TUHS] Additional groups and additional directory permissions

arnold at skeeve.com arnold at skeeve.com
Fri Aug 2 18:35:30 AEST 2019

[Subject line changed]


Doug McIlroy:
> Yet clean as the idea of groups was, it has been used only sporadically
> (in my experience).

I suspect this was true mainly at Research, where the whole place was
not large. Other people, as pointed out, found groups to be very useful.

"John P. Linderman" <jpl.jpl at gmail.com> wrote:
> This changed when you
> could be in multiple groups at the same time (a BSD invention?),

Yes, at 4.2 BSD. The so-called group set.

> and your
> primary group automatically changed to the group owning your current
> working directory (iff you belonged to that group).

No. Your process simply carried around a bunch of groups with it, and if
the group of the directory matched the primary group or a member of the
group set, you got group permission.

Arthur Krewat <krewat at kilonet.net>:
> There's also the setgid bit on directories, that when files are created, 
> they will be in the group that the parent directory has on it.

IIRC this was a Sun invention. It was in SunOS 4.x, and may even have
been in SunOS 3.x.

> Also, I don't think it's been mentioned, but there's the setuid bit on 
> directories - otherwise known as the sticky bit. When set, even if you 
> have rights to "write" the directory (meaning, delete files), you can't 
> delete those owned by other users. Useful for /tmp

Also a SunOS invention, IIRC.

> I have no idea what the timeline is for either of these features :)

Timeline is late 80s, SunOS 4.0, I believe. (Larry? :-)

These ideas later propogated into SVR4 / Solaris, Linux and most (if not all)
the other proprietary Unixes.



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