root access worked on my EC2 instance for a couple of weeks until I did
sudo aptitude update
sudo aptitude upgrade
and now sudo asks for a password (which I have never been given). I can't log in as root (says "Please login as the user "ubuntu" rather than the user "root".").
Does anyone know a way out of this mess ?
SOLVED: the solution is here in the accepted response: Amazon EC2 asking me to move AMI, how to go about doing it?