"If you forget system Login password in UBUNTU system, You can Recover it back by the following trick"
-Turn your computer on.
-Press ESC at the grub prompt
-Press e for editing.
-Highlight the line that begins kernel
-Press e
-Go to the very end of the line, and add rw init=/bin/bash
-Press enter,and then press b to boot your system.
-Your system will boot up to a password-less root shell.
-Type in password username
-Set your password.
-Type in reboot
Note: This "Password Recovery Trick" was not prepared or explained by me, After I got a query...