If you have forgotten or lost your root password and unable to login to your Ubuntu 14.04 linux system then follow the instructions below to recover your root password. First reboot/reset your system to GRUB2 boot loader menu. Navigate to the menu item you normally boot you Ubuntu system from and press "e" for edit.
Step 2 - Modify boot options
Find the line which starts with "linux". Navigate to the end of the line and add:
as illustrated on the screen-shot below:
Step 3 - Boot your system
Once you have changed boot options as indicated in the previous step press F10 to instruct your Ubuntu system to boot. Your system will boot and you will be provided with root command line prompt.
Step 4 - Reset your Lost Password
Once you get to the command line prompt enter the following linux command
# mount -o remount,rw /
HERE YOU CHANGE YOUR PASSWORD
# reboot -f
Lost Password Recovery complete.
Step 5 - Login with your new password
Once you reboot login as root user with your new password.