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 [email protected]
with a subject of "unsubscribe". Trouble? Contact [email protected]
