root priv in Terminal (Ubuntu)

[Michael Hoy]

I lost all my old emails so I can't respond to my last one about the 
lost drive space. Basically I just reinstalled windows and gave up on 
dual boot.

Now I'm using virtual box to run Ubuntu. I've got it installed, but 
having trouble gaining admin privileges  in  a terminal window. Perhaps 
I'm not typing it right.

I'm trying: su
then typing the password, but it says Authentication Failure. I'm using 
the same password I would use when prompted for it in graphical. Is 
there some other command to gain root in terminal on Ubuntu?