When attempting to do a backup using the “Rsync over SSH” option the following error is reported.
ERROR (root@localhost) Error performing backup or restore; rsync returned failure, rc='255', out='rsync: connection unexpectedly closed (0 bytes received so far) [sender] rsync error: unexplained error (code 255) at io.c(235) [sender=3.1.2]'
Rsync over SSH is not configured correctly. The public key from the Authentication key was not imported to the remote server.
The Admin Guide details how to create a backup policy using Rsync over SSH.
Step 8 has the following requirement.
“The public key of this keypair must be imported to the remote server.”
To import the public key to the remote server.
To troubleshoot an "Rsync over SSH" connection using public key authentication please see the following KB article.