A crashed startup disk? Keep calm and carry on finding a fix
Last Thursday morning I tapped the keyboard to awaken my Mac, and nothing happened. So I held down the power/eject key until I heard the comforting startup chime and soft whirring of fans.
My comfort was short-lived. When I tried to launch any app, I got a message that the app was damaged and couldn’t be opened. I also noticed that all of the previously colorful icons in my dock were replaced with gray question marks, telling me the dock couldn’t locate the apps.
I remained calm while performing the usual tricks and techniques you perform when your Mac goes wonky:
• I rebooted. No help.
• I rebooted again, just in case. Again, no help.
• I tried zapping the NVRAM by restarting while pressing Command + Option + P + R. That didn’t help, either.
• I tried a safe boot by restarting while pressing the Shift key. That didn’t help, either.
• I booted from a clone of my startup disk (cloned the night before), and then used Carbon Copy Cloner to clone it back onto my (original, internal) startup disk.
Somehow, that made things worse. When I restarted the MacBook Pro, the Apple logo and progress bar appeared briefly, and then the screen went black and stayed that way.
The fans were still whirring, so I thought something might be going on behind the scenes. I waited an hour, but nothing changed.
I was unfazed. I figured that the operating system was hosed, so, I booted into macOS Recovery mode by restarting while holding down Command + R. In Recovery mode, I first ran Disk First Aid on the recalcitrant disk. After it passed the tests, I reinstalled High Sierra.
Holding my breath, I rebooted (for about the 20th time), only to see the Apple logo (briefly), followed by the black screen of death. Again.
Now I got serious. I put my MacBook Air into Target Disk mode and connected it to the MacBook Pro via Thunderbolt. I restarted the MacBook Pro while holding down the Option key, and selected the MacBook Air (in Target Disk mode) as the startup disk for the MacBook Pro.
I ran my go-to third-party disk utilities — DiskWarrior and Drive Genius — but neither found any issues.
At this point I decided to erase the uncompliant drive and start over. I restarted into Recovery mode, erased the troubled drive, and reinstalled High Sierra.
Bingo. It turns out that erasing the disk before reinstalling High Sierra was the solution.
It took the better part of four hours before everything was back to normal. But because I had good backups and stayed calm, I was back to work within a few hours without losing a drop of data.
It wasn’t fun, but in retrospect, it could have been a lot worse.