I upgraded my docker container from linuxserver/duplicati:2.0.7 to linuxserver/duplicati:2.0.8. Since then, my backups are not being made and I get this error (now the second day):
[Error-Duplicati.Library.Main.Operation.BackupHandler-FatalError]: Fatal error HostKeyException: Validation of server fingerprint failed. Server returned fingerprint "…". Cause of this message is either not correct configuration or Man-in-the-middle attack!
The fingerprint is correct, and I don’t think it is a man-in-the-middle attack, as it only appears since the update to 2.0.8.
I haven’t done anything yet because I am afraid of messing things up.
If you see message that ssh-ed25519 32 host key has changed to an ssh-ed25519 256, with values to the right staying the same, this was a bug fix in SSH.NET to now display key’s length in bits, not bytes.
Alright, so I could fix it. Very easily. I think you were right about the “changed host key”.
Solution: Open Duplicati, edit the configurations of your backup, then go to Destination and hit Test connection, you will get a modal that offers to change the host key, hit OK and save the settings. Manually trigger a backup job and everything should work again.
