With a verifiably perfect System volume and firmware, if the Data volume has remained unmounted during the update, what could possibly have changed? The answer lies in what really does happen during a macOS update.īig Sur and Monterey run almost all their system software from the mounted snapshot of the System volume, but not everything can be installed there. In its Platform Security Guide, Apple states: “Finally, the user’s data volume is never mounted during a software update, to help prevent anything being read from or written to that volume during updates.” What’s confusing here is that Apple’s official word is that a modern update doesn’t alter the file system or data on the Data volume. Most of the problems experience by users, though, are more likely to be attributable to changes or errors in the Data volume, which isn’t sealed. At least on T2 and Apple silicon Macs, every byte in that snapshot is checked against a tree of cryptographic hashes, and only if the Seal at the top matches that prescribed by Apple will that system be bootable. But however they achieve it, at the end the snapshot your system runs from has to be bit-perfect.

While traditional macOS updates were fairly simple to understand, these modern updates are more complex. But since Big Sur, with the introduction of the SSV (signed and sealed System Volume), updates should have become extremely reliable. If you’re unlucky and a firmware update turns sour, or your Mac’s internal storage gets scrambled completely, then that’s fair cause. Updating macOS is widely held responsible for all manner of problems.

Spoof the installer mac os 10.12