When trouble strikes a disk image, macOS normally refuses to accept and mount it. This details how to use hdiutil to attach the image as a device so it can be repaired by fsck_apfs.
diskutil
They come in a multitude of formats and variants, and are used throughout macOS and apps. How do you use them, and what should be wary of?
ASIF disk images are new in Tahoe, and promise to be space efficient, as they’re sparse files, and almost as fast as the disk they’re stored on. Ideal for VMs and general use.
What separates System and Data volumes, and how does macOS know they’re part of a boot volume group? What distinguished backup volumes, and what is Sidecar?
How to tell whether someone has been eating the (APFS) porridge on one of your disks, using Get Info and DiskUtility’s First Aid. And a surprise hidden volume from 3 years ago.
APFS or HFS+? Which can Time Machine back up to? What about hard disks? Which format for use on PCs? And which are supported by Disk Utility now?
This reference covers fsck_apfs, diskutil information, diskutil apfs, conversion of HFS+ to APFS, mount_apfs, and newfs_apfs.
What’s in APFS, and what are its tools? How to interpret the version number, and what do we know has changed with different versions? How compatible are they?
Repairing permissions has a long history in Mac OS X. The permissions concerned have changed over the years, and it’s no longer what it once was.
Here’s an APFS (Encrypted) volume that isn’t encrypted, and an unencrypted volume with FileVault active. Something must be wrong.
The Eclectic Light Company 