Normal users, for the most part, can modify only the files they own. One special user, called the superuser or root, has full access to the machine and can do anything on it. To become the superuser, log in as yourself and type:

$ su -l
Password: *******
#

You will be prompted for the superuser password (which we presume you know, if it’s your computer). Your shell prompt will change to a hash mark (#) to indicate you are the superuser. When finished executing commands as the superuser, type ^D or run exit to end the superuser shell and become yourself again.

If you provide a username to su:

$ su -l sophia
Password: ********

you can become that user (provided you know her password).

$ sudo rm protected_file
Password: ********         Your own password