Stack Overflow (Ask Different) to the rescue

This is another one of those notes to me-from-the-future, but perhaps it will help someone else, too.

I was trying to install Apple’s Security Update 2019-005 on my old MacBookPro, which is running High Sierra (and can’t go to anything newer). When I tried to install the update, the machine never shut down properly; the display went black except for an arrow cursor, and it would stay that way indefinitely. Strangely enough, I could SSH into the machine while it was in that state and even shut it down – but when it rebooted, it would come up in normal mode without having installed the update.

I tried many things to fix the problem:

• Turned off Spotlight (sudo mdutil -a -i off) because mds and mdworker processes were using a lot of CPU
• Booted into recovery mode and ran Disk Utility in case there were any problems (there weren’t)
• Booted into recovery mode and reinstalled the OS
• Manually reinstalled Safari 13.0.1

but no matter what I did, the machine still hung when I tried to reboot it.

Eventually, after much searching, I found this Ask Different post and tried the commands it suggested:

sudo rm -rf /var/folders/zz/zy*
sudo shutdown -r now

and it worked – the machine rebooted into the installer, and a few minutes later, the system was up and running at the proper level (build 17G8037).

Thanks, Damian Krawczyk!