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macos apfs preboot bless

After converting your MacOS hard disk to APFS, you could run into a situation where your Mac is no longer bootable and you get errors like “Building boot caches on boot helper partition failed” or “Running bless to place boot files failed”. In my case, I restored a recently repaired Mac from a Time Machine backup and even though the backup had MacOS Mojave, it didn’t use the APFS file system after the restore, so Mojave couldn’t install any updates. After booting into recovery, I was able to convert the SSD to APFS, but then I couldn’t select it as the startup disk because I would get these errors. I couldn’t even run the Reinstall MacOS option because it would give me errors about preboot.

Convert Mac SSD to APFS

  • Boot into recovery using Command+R at startup
  • Select Disk Utility
  • Select your Macintosh HD (or whatever your’s is called)
  • Click the Unmount button
  • Click Edit then Convert to APFS

How To Fix Boot Errors After Converting MacOS To APFS

  • Boot into recovery using Command+R at startup
  • Go to Utilities > Terminal
  • Use this command to update the Preboot section of the disk to APFS
    diskutil apfs updatePreboot /Volumes/Macintosh\ HD/
    Replace “/Macintosh\ HD/” with the name of your boot volume
  • Exit Terminal and restart
    When Prompted, select your disk and you shoot be able to boot to it now

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