How to Reset your Linux Root Password

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 (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