Don't know my database username and password apparently

I am on Ubuntu and am trying to run ./install_amp from /usr/src/freepbx-2.5.2

I keep getting “Cannot connect to database” error when I try to run ./install_amp

I can login to mysql as root from the command line, but when I specify ./install_amp --username=user --password=pass (substituing the actual credentials for user and pass of course), it fails. Is there a default? How can I get this to work?