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.
fsck_apfs
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.
Safe mode is claimed to do 3 things: block 3rd party extensions, clear caches, and check your startup disk. But what disk checks does it really make, and how are they different?
First Aid in Disk Utility, or running fsck_apfs in Terminal, return warnings or errors on one of your Mac’s volumes. Here’s what to do next.
Should you run First Aid on your Data volume before updating macOS, or as routine housekeeping? And how should you run it?
What disk checks are made in Safe mode? How are they different from those run during normal startup? If Disk Utility is to be our only APFS repair tool, shouldn’t have more and better features?
What if you want to boot your Mac using two or more different versions of macOS, with different versions of APFS? Here’s how to avoid problems.
This reference covers fsck_apfs, diskutil information, diskutil apfs, conversion of HFS+ to APFS, mount_apfs, and newfs_apfs.
Two problems undermine Disk Utility’s First Aid: it persisting bug in failing to unmount volumes to check and repair, and its default omission of containers. And errors in APFS seem to be on the rise.
How to use First Aid in Disk Utility to check and repair APFS storage, whether it’s part of your boot disk, or general storage.
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