In some case if you have lost your administrative account access on Ubuntu, you can reset it within clicks. Follow below steps to reset password.
- Restart you Ubuntu system.
 - On Grub loading screen press ESCto view list.
 - Now select “Advanced options for Ubuntu” and press enter.\
 - Now select (recovery mod) option and press enter.
 - Here you will see Recovery menu. Select “Drop to root shell prompt”.
 - Change password of your administrative user. In this example, I am changing password of user “root”
 - In case if you get error like below:
 
[wpfmb type=’error’ theme=2]passwd: Authentication token manipulation errorpasswd: password unchanged[/wpfmb]
- remount your file system in read/write mode using following command and try reset to password again.
 
root@ubuntu:~# mount -o remount,rw /
Done!!