Step 2. If grub has password press "p" and enter the password or select and click "enter" to select the kernel you want to login.
Step 3. Select the line starting with "kernel" and press "e" to edit.
Step 4. Add the word "single" to the end of the line and click escape to save. Press "b" to boot with the modified grub entry.
Step 5. Linux will boot into the shell without any password prompt. Use the command "passwd root" to reset the root user password.
Restart and login with new root password.