I have a bundle of directories and sub-directories which I want other group
member to share. How could I set the directories and sub-directory with
sticky bit but leaving the files in 0644 mode instead.

I have tries chmod -R 1775 to a directory but the results are that all the
underlined files' file permission is changed as well. Any sugguestion. Do I
really have to do it by hand?

And go a bit further how to set umask so that users who are going create new
directory under these diectories observe the same rules to directory and
file ie. directory is 1775 and file is 644. Any sugguestion is welcome.

David Kwok