Ok, i have a user "nas" on my ubuntu server. In his home directory i have a "shared" folder but I also want to let a user create their own folder at this level for personal use. so any user that logs in can create a folder that they will have exclusive (unreadable by anyone else) access to, and if they want to share something they put it in the shared folder. How would I achieve this? I was reading about the permissions on the /tmp directory using setuid and think that may be a clue to it...
Option 1: Make the top-level directory world-writable.
Option 2: Make the top-level directory owned by root. Create a subdirectory for each user when you create their account.