[Bug 927218] Re: Unable to unset setguid bit

[Andrew McCarthy]

Thanks for taking the time to report this. The behaviour you describe
may seem surprising (and it was to me, too!), but is actually what the
man page describes:

       chmod preserves a directory's set-user-ID and set-group-ID bits  unless
       you  explicitly  specify otherwise.  You can set or clear the bits with
       symbolic modes like u+s and g-s, and you can set (but  not  clear)  the
       bits with a numeric mode.

So, you can clear the setgid bit on the directory in your example with
"chmod g-s Y", but not with "chmod 0775 Y". Since this is the defined
behaviour that others may have come to expect for both interactive use
and in long-established scripts, it's unlikely to be changed now.

** Package changed: bash (Ubuntu) => coreutils (Ubuntu)

** Changed in: coreutils (Ubuntu)
       Status: New => Invalid

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https://bugs.launchpad.net/bugs/927218

Title:
  Unable to unset setguid bit

Status in “coreutils” package in Ubuntu:
  Invalid

Bug description:
  In Precise, it is possible to set the guid bit for a directory but not
  to unset it.

  $ chmod g=rwxs Y
  foo at precise:/tmp/X$ ls -l
  total 4
  drwxrwsr-x 2 foo adm 4096 Feb  5 18:48 Y

  foo at precise:/tmp/X$ chmod g= Y
  foo at precise:/tmp/X$ ls -l
  total 4
  drwx--Sr-x 2 maintenance adm 4096 Feb  5 18:48 Y
  foo at precise:/tmp/X$ chmod g=rwx Y
  maintenance at precise:/tmp/X$ ls -l
  total 4
  drwxrwsr-x 2 foo adm 4096 Feb  5 18:48 Y

  foo at precise:/tmp/X$ chmod 0775 Y
  foo at precise:/tmp/X$ ls -l 
  total 4
  drwxrwsr-x 2 foo adm 4096 Feb  5 18:48 Y

  ProblemType: Bug
  DistroRelease: Ubuntu 12.04
  Package: bash 4.2-1ubuntu1
  ProcVersionSignature: Ubuntu 3.2.0-14.23-generic-pae 3.2.3
  Uname: Linux 3.2.0-14-generic-pae i686
  ApportVersion: 1.91-0ubuntu1
  Architecture: i386
  Date: Sun Feb  5 18:52:29 2012
  InstallationMedia: Ubuntu-Server 12.04 LTS "Precise Pangolin" - Alpha i386 (20111129)
  ProcEnviron:
   LANGUAGE=en_US:en
   PATH=(custom, no user)
   LANG=en_US.UTF-8
   SHELL=/bin/bash
  SourcePackage: bash
  UpgradeStatus: No upgrade log present (probably fresh install)

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