can not log in after jessie installation (2 replies)

I installed Debian Jessie on a pogoplug e02 using deboostrap on a different pogoplug. But after it boots up, I could not log in as root in ssh or serial. I have tried the following, but none worked.
1. write to /etc/shadow
2. delete the second field in /etc/shadow for root entry
3. copy a known working /etc/shadow from a known working machine

anyone has any idea?

thanks in advance