APFS volume won't boot
iMac recently updated to High Sierra and at same time, boot volume migrated to APFS. Installed the driver for my Evoluent mouse (which did ask for a Security 'Allow") and following reboot, Mac stalls at the end of the startup progress bar. Force restart. Same thing. Safe Boot. Same thing. Started up in verbose mode. Attached screen shot shows what I'm seeing.
It gets to the line near the top that says "apfs_vfsoop_unmount:1846 all done going home" in the expected amount of time, but then stalls for several minutes on the next line about the AppleKeyStore and the special bag -503. then another few minutes to the get the 'apfs_keybag_get:1320: failed to get apfs volume keybag, err = 2'. The rest of the showed up over the next 30-40 minutes, where apparently it's looking for some snapshot data.
Can anyone make any sense of this? Is there a way to fix this APFS failure? How could installing a driver damage APFS to this extent?
You might try Single User mode then run an fsck to see what it reports. Or boot into recovery & run Disk Utility repair.
My suspicion is a corrupt APFS snapshot.
On my MBP I was experiencing extremely slow Safe Mode restart & disk checking and when I dived deeper into error messages I found that one snapshot was reporting an error. I had to clone/erase/reinstall/migrate to resolve that particular problem because there is not yet (as far as I know?) any 3rd party tool for repairing APFS.