[TUHS] Additional groups and additional directory permissions

arnold at skeeve.com arnold at skeeve.com
Sun Aug 4 16:40:47 AEST 2019

> arnold at skeeve.com <arnold at skeeve.com> wrote:
> > 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.

Tony Finch <dot at dotat.at> wrote:
> When Bill Joy added the "multi-group stuff" to BSD all directories became
> implicitly set-gid:

Yes.  But the commercial world had backwards compatibility to worry about.
Thus the setgid bit on directories. I'm no longer sure who first came
up with it.

> As I understand it, when group support was improved in System V they did
> not change creat() to match BSD but instead used the directory set-gid bit
> to provide opt-in BSD semantics. I don't know if this was in Solaris or
> earlier?

Correct, but not sure when it was first done.

> > > 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.
> BSD again :-) SCCS revision 6.6 so I think it appeared in 4.3BSD

That sounds right. I stand corrected.



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