#When you forget root password, there is a way to set a new password accessing the console after booting or restarting the system.
When grub load, edit the line kernel and add in the end of kernel parameters:
The system will go up without requesting root password like in single user.
After the system is up, re-mount / filesystem
# mount -o remount,rw /
Now the / filesystem is accesible and you can change root password with:
# passwd root
Now reboot the machine normally and let the system boot.