I am trying to flash OpenWrt to a pogoplug oxnas box using the snapshot uImage. However, I cannot log in, since there seems to be a pssword set for root (login without password gives "Permission denied", as does using "root" or "password" or "1234" as the password).
Thanks for your reply. However, I did not flash anything yet, I just loaded the kernel from a USB drive using netconsole. I changed that now to a uImage from 18.06.2 where I can log in. I guess, sysupgrade to a snapshot release should work from there, but I do not find the instructions at OpenWrt's product page particularly clear ...
Thus, I am currently trying to figure out exactly what to do in order not to mess things up.
You just described the instructions at Step 4. You seem to be comprehending them quite well. You could also install LuCI over the network and do the sysupgrade at the System > Backup / Flash Firmware page. If you need to inquire about flashing, consider making a new thread.
If your problem is solved, feel free to mark the relevant post as the solution.
Don't do that. It's a security risk to run things on your PC as root when you don't have to. All that needs to be done is tell the router you want to log in as root-- since in most cases the only defined user in OpenWrt is root.
This is done either with ssh email@example.com or ssh 192.168.1.1 -l root.
If you don't specify a remote user name, ssh by default requests a login as the same name you're running as on the PC.