I've called it a victory too early!
i've restored the entire / in the target machine, which means even the /root/.ssh folders, which led to an unmatching couple of ssh-rsa keys, and consequently the backup is not working after the restore.
I've successfully created 2 new ssh-rsa keys, following your tutorial, and now I get to log password-less as backuppc becoming root:
$ ssh -l root 192.168.1.1 whoami
Nonetheless, I get the same hideous error:
Running: /usr/bin/ssh -q -x -l root efbujagateway /usr/bin/rsync --server --numeric-ids --perms --owner --group -D --links --hard-links --times --block-size=2048 --relative --ignore-times --recursive . /
Xfer PIDs are now 15583
Read EOF: Connection reset by peer
Tried again: got 0 bytes
Done: 0 files, 0 bytes
restore failed: Unable to read 4 bytes
I really don't see how I can troubleshoot this any further
Where should I look? Which logs?