If you forgot your Ubuntu Linux User Password and unable to get in..here is how you can reset your password by following these simple steps..
Restart your Computer.
A GNU GRUB menu will appear.
Select the Ubuntu option. Do not click Enter.. just select the ubuntu option and press e on your keyboard to edit the boot parameters..
Then a box will appear.Find the line that start with Linux.
At the end of that line we will find something like this ro quiet splash $vt_handoff.
Remove this last line starting from ro and replace it with rw init=/bin/bash.
After writing this command press ctrl+x or f10 to boot with the modified parameters.
This will boot you into a root shell prompt without requiring a password.
If you want to see the partition type mount | grep -w /
Now you can reset the password for any user account using the passwd command..
passwd kitty
Replace kitty with the actual username for which you want to reset the password of your ubuntu user.
After resetting the password, remount the filesystem as read-write..
mount -o remount,rw /
Type sync to flush any pending write to disk..
we will reboot our system..
reboot -f
you should now be able to log in with the new password for the specified user account. :)