If you use rsync to backup your system, and the system you’re backing up to has different uids for some userids, it converts them as it stores! I just found this out because after restoring my xen1 backup, I’ve discovered that all my postgres files belong to 114, which is the uid of postgres on my home server, not on xen1.
This is going to make restoring all the xen backups a royal pain in the ass.