Access to rootfile system fails

Hello,

I am trying to access to my emdebian rootfs built using the steps 
described below (multistrap):

http://www.acmesystems.it/multistrap

I have a promt, but I don't know how i can log as root...

As the website describes, I have typed this command to set the root 
password:

*sudo chroot target-rootfs passwd*

However, if a type login:root, it does not work.

I really appreciate your help.

Best regards,

G.D