Look at this from Fedora FAQ -
Q:How do I reset my root password?A: If you’ve forgotten your root password, and you want to change it, don’t worry! It’s possible. You need to boot into what’s called “single-user mode.” You must be in front of the computer to do this – you can not do it remotely:
- Using the instructions in the runlevel question (under the “While You Are Booting the Computer” section), boot into runlevel 1.
- Set the new root password with by typing: passwd
And then enter your new root password when asked.
- Reboot your machine, and you will now be able to log in as root with the new password that you entered.
And here’s that runlevel question -
While You Are Booting the Computer:
- When you first start your computer, the GRUB screen (where you choose your Operating System) appears. Select the Fedora that you want to boot into, but press the a key instead of pressing Enter.
- You will see a line somewhat like the following: kernel /vmlinuz-2.6.9-1.667 ro root=LABEL=/ acpi=on rhgb quiet
Add the number of your runlevel to the end of that line, and then press Enter. For example, to boot into text-only mode, the line would look like:
kernel /vmlinuz-2.6.9-1.667 ro root=LABEL=/ acpi=on rhgb quiet 3
You will then boot into the new runlevel this time only.
This just shows how easy it is hack into our systems unless we secure our grub!