I am using Ubuntu 16.04.1 LTS through the Oracle VM Virtualbox. At the beginning of my installation, I was asked to set a password for my login, which works perfectly every time I log in to my virtual box.

However, when I tried today to change my password with passwd, I get the following error messages:

passwd: Authentication token manipulation error
passwd: password unchanged

Therefore, I cannot change my password. The point is that I am pretty sure I am typing correctly my password since it is also my log-in password (it consists of characters [some in upper case], numbers, and an asterisk *).

Is there anything I could do to find out what's happening or a way to change my password?

PS: Everything began from my attempt to use sudo -, where again my typed password gets rejected.