Wednesday, June 30, 2021

Why You Can’t Roll Back Big Sur’s System Volume

Howard Oakley:

If you as a user make a snapshot of the System volume, you’ll get an unsealed replica of the System volume that can’t be used to replace the new sealed snapshot, and hasn’t even been blessed to make it bootable. Trying to roll back to that would only end in failure.

What has been tried earlier in Big Sur is preserving the previous bootable sealed snapshot rather than deleting it once a macOS update has been completed. This isn’t a cheap option, though: it would probably require up to 15 GB of free space on the System volume. Because of that, macOS would need to remove it automatically after a period of a week perhaps, which sets a time limit on its use for a rollback.

It’s unclear why Apple doesn’t provide an option in its updaters to automatically preserve the old snapshot for a maximum of one week, to support rollback over that time. Unfortunately, it’s not something the user can achieve any other way.


3 Comments RSS · Twitter

Why didn't Apple simply delay this feature until they had tooling to seal and bless old snapshots? What was the pressing need?

Harald Striepe

Hi Howard!
One problem is that not just the system volume is updated, but in some cases also user databases suh as Mail and the Music library. Rolling back means you would have to initialize those from scratch.

With some care, all of this could be handled, but Apple NEVER LOOKS BACK!

@Harald With Mojave (I think it was) you could roll back everything at once (system and user, all on the same vlume), so the databases would remain consistent with the version of the OS that was running. It seems like this could still be done, just by snapshotting two volumes instead of one.

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