Demonstrated 10 years ago as a major new feature in APFS, and capable of blazingly fast rollback preserving data including document versions, snapshots still aren’t fully accessible or documented.
APFS
Introduced in Mac OS X 10.4 to extend resource forks, they have flourished since. Explains their storage, how they persist or don’t, with an appendix explaining their flags.
If you’ve installed the new Creator Studio versions of Keynote, Numbers and Pages you’ll have noticed those apps have the same name as the iWork ones, and can sit side-by-side with them. What trickery was used to do this?
Should you attempt a repair in Recovery mode? Is it just a warning? How to identify the file or folder with a problem, and what to do to fix or prevent it from recurring.
If you’ve upgraded to Tahoe, your Time Capsule should still back up normally. But erase it to start new backups, and Time Machine refuses to back up to it any more.
After the Boot ROM, LLB and iBoot (stage 2), kernel boot starts setting up security services and putting the hardware to work. CPU cores are started up before file systems are mounted, and the Mac starts userspace boot.
As Time Machine has changed, first to back up APFS volumes, then to create backups as snapshots, its needs have changed. This makes it complicated to decide which local snapshots you can delete without affecting its backups.
Fundamentally simple: a preserved copy of a volume at a moment in time. How its size can only increase with time, how they’re managed, what they’re used for, and the tools for using them.
It makes a big difference whether an app, file or folder is in the System or Data volume, or maybe somewhere else. Here’s how to tell accurately, rather than according to one of the Finder’s illusions.
How to read a UUID to determine whether it’s supposed to be random, or has a specific meaning. Where you’ll find them, and whether you’ll ever see two the same.
The Eclectic Light Company 