Very interesting. Upgrade to PR1.2009.51-1, and restored backup, everything worked, so far, upon SSH, "...authentication failed.", password has been changed, or password has NOT been restored.

no sweat, do some guessing work, it turned out, it used the generic one, "rootme"

Anyhow, just in case, whatever reason you need to change your password for root, but does not know the password, you can do this, it does NOT require you to know the password, very strange (?)

xterm
sudo gainroot
passwd
type a new password
re-type the new password

password changed.

I still puzzled by the fact, that you do not need to know the password in order to change to new password. Witchcraft.

bun

Root is never asked for the existing password when changing a password because as root - linux does not question you. What root says, linux does. Which is why having root is both incredibly dangerous, and powerful.

Sudo gainroot is configured to not prompt the user for a password to, naturally, "gain root". Normally, sudo WOULD ask for a password.. however this was intentionally configured not to both because there is no passwords on the device by default... and it's simply easier.