Whenever you can’t remember your Root password, you can do this steps to reset it.

You can log in with single-user mode and create a new root password.

Reboot your computer. When GRUB is presenting the menu list, follow those instructions:

use the arrows to select the boot entry you want to modify
press e to edit the entry
use the arrows to go to kernel line
press e to edit this entry
at the end of the line add the word single (there should be a space between like / single)
press ENTER to go back to the parent menu
press b to boot this kernel

As root, changing password does not ask for your old password. Now, you can change root’s password by typing:

bash# passwd root

You’ll be asked to re-type the password for verification. Once you’re finished, the password will be changed and you can reboot by typing shutdown -r now at the prompt; then you can log in to root as before

If your boot loader is LILO follow this

At LILO boot loader type linux single and press [ENTER] key:

Boot: linux single

When you get the # prompt you will need to type passwd root to reset password:

# passwd root

Reboot system:

# sync
# reboot