[TUHS] Additional groups and additional directory permissions

Tony Finch dot at dotat.at
Fri Aug 2 21:18:30 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.

When Bill Joy added the "multi-group stuff" to BSD all directories became
implicitly set-gid:


This is in SCCS revision 4.8 so I think it appeared in 4.2BSD

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

> > 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


f.anthony.n.finch  <dot at dotat.at>  http://dotat.at/
Mull of Galloway to Mull of Kintyre including the Firth of Clyde and North
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