File create permissions, what am I missing?

Mike Meyer mwm-keyword-hackers.e471b2 at
Sat Aug 13 00:13:33 GMT 2005

In <20050812233728.GA22225 at>, Brooks Davis <brooks at> typed:
> On Fri, Aug 12, 2005 at 06:34:34PM -0300, João Carlos Mendes Luis wrote:
> > In a directory with -rwxrwxrwx, any user can create files, but who should 
> > be the owner/group of this file?
> > 
> > Long time ago in Unix history, the owner would be the user who created the 
> > file, and the group would be the users's primary group.
> > 
> > Later, IIRC, if the directory group was one of the user's secondary groups, 
> > the file would also be from this group.
> > 
> > A later modification defined that a setgid directory would effect in all 
> > files created belonging to the directory's user.
> > 
> > Am I correct?
> > 
> > But I have already tested 3 system, 2 with 5-stable and 1 with 4-stable, in 
> > which the created file inside a -rwxrwxrwx directory is created belonging 
> > to the directory's group, WITHOUT the setgid bit.  What did I miss?
> On BSD systems, the group of a file is always the group of the directory
> it is in.  This differs from SysV UNIX.  The resident grey-beard at work
> feels this is a new and annoying behavior. (i.e. it wasn't always this
> way. :)

SysV lets you toggle that behavior on a per-directory basis. Turn the
setgid bit on in the directory, and files created in it will be owned
by the group that owns the directory.

Mike Meyer <mwm at>
Independent Network/Unix/Perforce consultant, email for more information.

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