I follow instructions on Gumstix Wiki to install Ubuntu 10.04 onto Gumstix Overo.  Installation was success and system booted correctly.  At the user prompt, I cannot login as root.  So I follow instructions from the wiki:

The rootstock utility doesn't make passwords properly. For now, it is easiest to remove the root password, boot your system to create new users and choose a new root password. To do this, open the /etc/shadow file on the second partition and delete the '*' for the root entry. E.g.
$ sudo gedit /path/to/second/partition/etc/shadow
Note: remember to put the ‘*’ back after you have created a user so someone can’t login as root and screw up your system

but I have no shadow file in this path!  I created an empty shadow file, and re-booted Overo.  Still same problem, cannot login as root or as any other user.  What can I do?  Do I also need to edit  /etc/passwd ?