[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]
Hi.
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.
HTH,
Arnold
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