Path: utzoo!attcan!cmtl01!matrox!uvm-gen!uunet!lll-winken!ames!pasteur!ucbvax!decwrl!decvax!eagle_snax!geoff
From: geoff@eagle_snax.UUCP ( R.H. coast near the top)
Newsgroups: comp.protocols.tcp-ip.ibmpc
Subject: Re: pc-nfs group access permissions
Summary: it works, but it's easy to go wrong.
Message-ID: <452@eagle_snax.UUCP>
Date: 25 Jan 89 13:46:33 GMT
References: <3031@uhccux.uhcc.hawaii.edu>
Reply-To: geoff@eagle_snax.UUCP (Geoff Arnold @ Sun ECD - R.H. coast near the top)
Organization: Sun Microsystems - East Coast Division
Lines: 49

In article <3031@uhccux.uhcc.hawaii.edu> richard@uhccux.uhcc.hawaii.edu (Richard Foulk) writes:
>I'm trying to use unix group permissions to allow two PC users on
>our network to share files (read and write).  According to the
>pc-nfs manual a single group is supported.  Unfortunately, so far
>my attempts to make it work have failed.
>

When I read your posting, I sat down to try it at once. I began by
creating a directory from Unix, then mounting the file system and
CHDIR'ing to it on DOS with a different UID but the same GID. Ooops -
it DOES seem to be broken. Then I tried again, but created the
directories under PC-NFS. This time, it seemed to work. What's
going on here?

What I was running into (and what I suspect that Richard encountered)
is one of the more common misunderstandings under BSD-based Unix
systems. When you create a directory...

     The directory's owner ID is set to the  process's  effective
     user  ID.   The  directory's  group ID is set to that of the
     parent directory in which it is created.

from mkdir(2) under SunOS 3.2 - under SunOS4.0 it's different:

    The directory's owner ID is set to the  process's  effective
     user ID.
 
     The directory's group ID is set to either:

          +  the effective  group  ID  of  the  process,  if  the
             filesystem  was  not  mounted  with  the  BSD  file-
             creation semantics flag (see mount(2)) and the  set-
             gid bit of the parent directory is clear, or

          +  the group ID of the directory in which the  file  is
             created.

PC-NFS always sets the GID to that of the "creating process" (i.e.
the user's GID from "net name"). Many folks assume that this
happens under Unix, but 'taint necessarily so...

Geoff


-- 
Geoff Arnold, Sun Microsystems Inc.  | "It is well known that the longer one
PC Dist. Sys. Group (home of PC-NFS) |postpones a pleasure, the greater the
UUCP: {hplabs,decwrl...}!sun!garnold |pleasure when it arrives. Therefore, if
ARPA: garnold@sun.com                |one postpones it forever..." (Smullyan)