Sticky Bit

The sticky bit is a permission bit that protects the files within a directory. If the directory has the sticky bit set, a file can be deleted only by the owner of the file, the owner of the directory, or by root. This prevents a user from deleting other users' files from public directories such as uucppublic:

drwxrwxrwt   2 uucp   uucp   512 May 24 09:48 /var/spool/uucppublic

Be sure to set the sticky bit manually when you set up a public directory on a TMPFS file system.