How to Reset debian Root Password

if you forgot your password root debian server or debian desktop use the following procedure to reset.

• Boot into grub, select single user but do not press enter.

• Press "e" to go into edit mode.

• Scroll down to the kernel line, it starts with "linux /boot/vmlinuz-3.2……."

• Scroll to the end of that line and press space key once and typeinit=/bin/bash

• Press Ctrl X to boot

At this point, the root file system is still mounted read-only, so enter the following command:

#mount -n -o remount,rw /

Then type

#passwd

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

#reboot

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

Source:

http://www.debianadmin.com/how-to-reset-debian-root-password.html