sgid bit on dirs Was: Re: problems w/pppd 2.3.7

[rir@mediaone.net]

On Wed, 14 Apr 1999, Jeremy wrote:
> On 14 Apr 1999, John Hasler wrote:
> 
> > Jeremy writes:
> > > drwxr-s---   2 root     dip          1024 Apr 12 08:17 /etc/chatscripts
> > > ...
> > 
> > Set group ID on execution on a directory does nothing useful that I know
> > of.  The group needs execute permission to search the directory:
> > 
> > drwxr-x---   2 root     dip          1024 Apr 12 08:17 /etc/chatscripts

The following applies to linux, and I suspect to most recent
versions of unix.  This info is should be more well known.

The set group id on a directory aids in the sharing of files under
a directory by forcing created files to take on the same group ownership
as the directory.  If root creates a file in Jeremy's /etc/chatscripts 
example, the ownership will be root.dip not root.root.

A related point:

The sticky bit on a directory prevents another user from
deleting your file, unless he owns the directory.  
Good for TMPDIR's:

    drwxrwxrwt   2 root     root         1024 Apr 15 08:90 /tmp