Hi! A friend just recommended the backup tool that comes with Ubuntu. I took a look at it and was wondering what you guys include and exclude from the backups. I just installed wire guard VPN and but the config file in the etc/wireguard folder, where it belongs. I would have to include this folder as well if I want to keep my configs. And I guess many programs do the same, so how do you know what to include, so you can just revert to the last backup if something breaks or you get a new machine? Maybe that is a stupid question, but it was going through my head for some time now. Thanks a lot!
Because if you’re not offline, something is writing to the filesystem and changing blocks while you’re copying. If you’re lucky what you copied would be outdated. If you’re less lucky it would cause fs inconsistency which would be cleaned up by fsck. If you are even less lucky you’d end up with silently corrupted files, e.g. a text file with old parts mixed with new. If you’re even less lucky, you’d hit a vital metadata part of the fs and it would not be mountable anymore.
To clarify, the filesystem being block-copied has to be offline or mounted RO, not the whole OS. However if that’s the root/home filesystem, then you can’t unmount it while the OS is online.
If you don’t want to deal with that you need a filesystem or volume manager that supports snapshots, then you can copy the snapshot. E.g. snapshot your root LVM vol, then block-copy the snapshot.