howtos/files_directories/chmod.md

We are aware of permissions for the owner(u), group(g), and other(o), however the set-uid, set-gid and sticky bit are other special permissions.

setting	description
set-uid	setting uid on an executable file allows the file to be executed with the original owners permissions.e.g.A script owned by root is executed with root priviledges when run by an ordinar user
set-gid	in files, set-gid files are executed with the group's permissions, while in directories all new files belong to the group by default
sticky bit	In a shared environment, allows deletion only by the owner of the file

chmod u+s file  # sets uid, use - to unset
chmod g+s directory # sets gid
chmod +t   # sets the sticky bit
chmod 1770 directory # sets sticky bit, grants rwx permissions for u and g