How to Boot into single user mode

You can do that by modifying the grub boot option on startup.

1. Press 'e' to edit startup
2. Use the arrow keys to highlight the kernel line and press 'e' to edit the parameters
3. At the end of the line, add the word 'single' (without the ' ) and press Enter
4. Press 'b' to boot the system

GRUB will boot single-user Linux mode. After it finishes loading, you will be presented with a shell prompt similar to the following:

You can now change the root password by typing