Setting the group ID for file creation in a directory
By default, the GID (group identifier) of a newly created
file is set to the GID of the creating process or user.
Setting the SGID bit on a directory causes all subsequent
new files to take the GID of that directory.
This makes it easier for users to share files, because it ensures
that all files will have the same GID, even if the users
don't have the same login group.
To set the SGID bit on a directory, use this command,
substituting the directory name for directory:
chmod g+s directory
To remove the bit, replace the ``+'' with a ``-'' in the chmod command.