Apple recently released macOS 11.2, which is supposed to help with some bluetooth issues. I was eager to update ASAP, but my MBP had other ideas.

The problem

My mac could download the update, and was able to complete the "preparing" stage... but any time it rebooted to install, it ran into some kind of problem. Then it prompted me to download the update again, let it prepare the update again, and reboot to try again. Again, to no avail.

Troubleshooting

  1. The first thing I tried was going through the usual process, again. Download the update, let it prepare it, and try installing again. That didn't work.
  2. So I rebooted the computer, and then tried it all over again. That didn't help either.
  3. I looked online for ideas, but many required disabling system integrity protection. I wasn't ready for that.
  4. I thought that resetting the SMC and NVRAM sometimes fixes weird issues, so I gave that a shot. I shut down the mac, held Command, Option, P, and R, turned it on, got confirmation that it worked, and let the computer boot back to the login screen. Then I shut it down again and held the left Option, Command, and Control keys while holding the power button down for 10 seconds to reset the SMC. It worked too, so I let the computer boot to the login screen, typed my password and it... rebooted itself mid boot.
  5. Well crap, I made it worse. So I tried booting again. Same problem. I tried booting into safe mode, and got the same problem again.
  6. I drove to an appointment having nothing to do with this infernal computer.

The solution

It turns out I didn't actually make it worse. Resetting the NVRAM and SMC caused my mac to use the broken update partition as the default startup disk. I held option while booting to select the correct startup disk. Everything was back to normal. No data lost. For good measure, I took a new set of backups and copied some important data off of my laptop before doing anything else.

So what about the original update for 11.2? My mac recognized that the update didn't work. It downloaded the update again, went through the whole pre-update process again, and asked to reboot to install the update... again. And this time it worked. I'm now running macOS 11.2. I suspect the original problem was solved when resetting the NVRAM or SMC.

Takeaways

  1. Keep recent backups. I was worried that I lost a few days worth of virtual machine data that is excluded from my time machine backups.
  2. Sometimes resetting the NVRAM and SMC helps. It's probably not the first thing to try, but is good for low level issues, and apparently, OS updates that segfault without a stack trace.
  3. Resetting the NVRAM and/or SMC can change your startup disk. Be aware when dealing with system updates.
  4. Apple has documented all of the startup key combinations you can use for Intel macs.

Have you had issues installing macOS updates? Did this help? Did something else make it work for you? Let me know on Twitter.