Best Way to Upgrade to Disco Dingo 19.04 Using BTRFS Backups?

[PhysicistSarah]

I have my @home and @ folders backed up, and I'm insterested in upgrading to Kubuntu 19.04.

What's the best way to do this? I would imagine that I can't just replace the @/@home directories of the new install with the old one. Are more traditional methods more of use here like Aptik? Can the @home directory just be placed on the new OS without anything breaking? Or should I just make my backup read-write and transfer the files over?

[claydoh]

Do an in-place upgrade, instead of a clean install? Your home is not touched, and your existing volumes stay the same, and work the same. If there were a problem, just roll back to to your pre-upgrade backup and be back in your previous Kubuntu version.



caveat: I have zero clues about btrfs, but it seems to be extremely useful , and specifically designed, for these kind of situations.

I normally suggest most people wait a bit after the upgrade prompt comes, just to see if there are any issues folks may have.
I regularly ignore this suggestion myself though

[PhysicistSarah]

Oh, that's a great suggestion actually.

[jlittle]

The simple approach is to snapshot @ and @home to snapshots at the top level, that is the same level as @ and @home, then do the upgrade (do-release-upgrade), and check it out. If it's good, sweet, those snapshots become part of your snapshot strategy, to be managed as such. If not, rename @ to @_dud, @home to @home_dud, and rename the snapshots to @ and @home, reboot, then delete @_dud and @home_dud; takes seconds.

What I will do is a bit more:

1. Firstly, every release I run I rename @ and @home. F.ex. presently I have @_cosmic and @home_cosmic, and @_bionic and @home_cosmic. I have to adjust /etc/fstab (subvol=@ to subvol=@_cosmic and the same for @home) and set up a grub "menuentry" that points to @_cosmic.
2. I'll do backups, internal and external. Just to have a backstop.
3. I'll do a clean install of disco. (I could run ubiquity with the -b flag to stop it trampling my grub set up, but I solve that problem another way these days.) It will install to @ and @home, which I'll immediately rename to, say, @_disco_clean and @home_disco_clean, using step 1.
4. I'll snapshot @_cosmic to, say, @_disco_ru (ru for release upgraded) and @home_cosmic to @home_disco_ru, and adjust stuff like step 1. Then I'll boot into @_disco_ru and run do-release-upgrade there.

Then, I'll be able to boot to bionic, cosmic, a clean install of disco, and a disco upgraded from cosmic. Only the clean install will take all new space; the space for a lot of the bionic, cosmic, and upgraded disco installs will be shared under the hood in the btrfs. IMO the trickiest part is keeping grub under control, and I've posted here in KFN about the various tricks I use.