If you forgot your root password for your Debian server use the following procedure to reset. This has been tested on ‘Wheezy’

Press SHIFT on boot to get into the GRUB menu. Select the option to edit the commands (c?). Move the cursor down until you see the line starting ‘linux’ and append the text to below to that line. Press CTRL+x to boot the system.

You will shortly get the command line. At this point, the root file system is still mounted read-only, so enter the following to remount it READ WRITE –

Then type –

Enter your new password. Retype if asked to confirm.
Then restart the machine by typing –

Now you should be able to login with your new root password as required.