111、Enable the user(开启root账户)
assign the root user a password and thereby activate it

    sudo passwd root

Then type a new password that you’ll use in future when logging in as root user.
switch to root user at the command prompt by typing su
You won’t be able to login as root from the login window
Click System ! Administration ! Login Window, then click the Security tab, and put a check in Allow Local System Administrator Login. Then close the program and log out and back in again as root (provide root as your username). Note that running a GUI as root is about as dangerous as it gets but, then again,it’s your computer!