In case you want to backup a remote machine, which runs Ubuntu, and you do not want to grant root access to this machine you can tell rsync to run on the source (remote) machine as root.

Add --rsync-path="sudo rsync" so it looks like:

rsync -rltDv --delete --rsync-path="sudo rsync" source:/path target:/path

Just make sure the user you are connecting as on the source is able to sudo.