creating a new user or logging in as root from grub

In some circumstances it can be useful to create a new user when your having configuration issues and want to find out if user related configurations are the problem or if it gos further to the heart of your system:
To change the password, turn on the computer and press the ESC key when GRUB appears. Scroll down and highlight ‘Recovery Mode’ and press the ‘B’ key; this will cause you to enter ‘Single User Mode’.

You’re now at the prompt, and logged in as ‘root’ by default. Type ‘passwd’ and then choose a new password. This will change the root password to whatever you enter. If you’re interested in only gaining access to a single account on the system, however, then type ‘passwd username’ replacing ‘username’ with the login name for the account you would like to alter the password for.