Can't set root password on ALPHA9 for RPI3

[bob prohaska]

In setting up ALPHA9 on an RPI3 an error comes up in trying to 
set a password using single-user mode on the serial console.

Initially the machine came up  multi-user, whence I realized
I'd forgotten to set a root password. I pulled the plug and
booted to single user successfully. However, when I typed

# passwd
Changing local password for root
New Password:
Retype New Password:
passwd: pam_chauthtok(): Error in service module

Fsck says the filesystem is clean. I could re-image
the microSD card and start over, but would rather
save the configuration done so far if it's possible.

Thanks for reading, and any guidance!

bob prohaska