Whenever you can't remember Root password, you can read this TUTorial and do step by step 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
- press ESC 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.
Source: http://www.linux.org ; http://www.redhat.com/