How to reset root/single_user password in Ubuntu on a Virtual Machine

In order to access the grub menu on a virtual machine, you need to hold the shift key down for a while. You must let your virtual machine to capture your mouse before holding the shift key. Follow the steps to change your password:

1. Let your virtual Machine to capture your mouse.
2. Hold the shift key down to get the grub menu.
3. Select the recovery mode option.
4. Select drop to root shell prompt.
5. Now, change with # passwd [username] (You can also see the list of users using # nano /etc/passwd).