I'm using Deja-Dup to store my backups from multiple systems to my UbuntuOne subscription. I have setup weekly backups that should be keep at least 28 days. Yet it seems that Deja-Dup will keep the backups longer. I wish I could configure Deja-Dup to run duplicity's "duplicity remove-all-but-n-full" every time a backup completes with a configurable 'n'. I was now going to write a cronjob to do that as a workaround. But that command needs a URL probably with credentials. But I have no idea where to find the URL for the UbuntuOne storage. I have found some indication that scheme must be something like "u1+https://firstname.lastname@example.org/some/path" but I have no idea how to construct the URL for my account and how to add the account credentials.
According to the duplicity documentation:
The URL Format documentation suggests the url should take the form