Eight BSD flags are available in APFS to lock files, hide them, and restrict them in other ways. None of them synced correctly in iCloud Drive, and four caused other problems.
APFS
How to use the Finder’s Lock feature, and as the Immutable flag in Terminal. What its effects are, and how well it’s retained. How iCloud Drive can’t cope with it, and how you can use it in your own lightweight versioning system.
You’re in a rush, and need to disconnect your MacBook Pro’s external drive. But when you try to eject it, one or more programs may be using it. What do you do next?
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.
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.
The Eclectic Light Company 