Did you forgot root password in linux?
You are in login screen and u forgot root password? Don't worry..Follow these easy steps ..
1. Reboot, as soon as u see GRUB on screen press Escape. Highlight first entry and press ‘e‘.
2. Go to the kernel line (something like “kernel /boot/vmlinuz-. . .“) and press ‘e‘ again.
3. Using arrow keys, go the very end of the line and leaving one space, type: single
4. Press that ESC key again, and then press ‘b‘ key to boot your machine.
5. You will get a command prompt. Type "passwd" and give "yourpassword".
6. Thats it..u change the root password and reboot to login in normal mode. No need to change anything while grub comes.