Oh, for the archive I should also point out that this is also documented in the info pages. I will include a direct link to the documentation node.
Bob $ info coreutils 'Directory Setuid and Setgid' 26.4 Directories and the Set-User-ID and Set-Group-ID Bits ========================================================== On most systems, if a directory's set-group-ID bit is set, newly created subfiles inherit the same group as the directory, and newly created subdirectories inherit the set-group-ID bit of the parent directory. On a few systems, a directory's set-user-ID bit has a similar effect on the ownership of new subfiles and the set-user-ID bits of new subdirectories. These mechanisms let users share files more easily, by lessening the need to use `chmod' or `chown' to share new files. These convenience mechanisms rely on the set-user-ID and set-group-ID bits of directories. If commands like `chmod' and `mkdir' routinely cleared these bits on directories, the mechanisms would be less convenient and it would be harder to share files. Therefore, a command like `chmod' does not affect the set-user-ID or set-group-ID bits of a directory unless the user specifically mentions them in a symbolic mode, or sets them in a numeric mode. For example, on systems that support set-group-ID inheritance: # These commands leave the set-user-ID and # set-group-ID bits of the subdirectories alone, # so that they retain their default values. mkdir A B C chmod 755 A chmod 0755 B chmod u=rwx,go=rx C mkdir -m 755 D mkdir -m 0755 E mkdir -m u=rwx,go=rx F If you want to try to set these bits, you must mention them explicitly in the symbolic or numeric modes, e.g.: # These commands try to set the set-user-ID # and set-group-ID bits of the subdirectories. mkdir G H chmod 6755 G chmod u=rwx,go=rx,a+s H mkdir -m 6755 I mkdir -m u=rwx,go=rx,a+s J If you want to try to clear these bits, you must mention them explicitly in a symbolic mode, e.g.: # This command tries to clear the set-user-ID # and set-group-ID bits of the directory D. chmod a-s D This behavior is a GNU extension. Portable scripts should not rely on requests to set or clear these bits on directories, as POSIX allows implementations to ignore these requests. -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org