Stupid Mac Trick: Restoring from newer TM Backup over old OS

[mikehalloran]

Stupid Mac Trick — Restoring from newer TM Backup over older MacOS

Funny that I've never run into this before. Migration Assistant doesn't like to restore over an older MacOS (Mojave backup when HS is installed) be it a TM volume or another Mac. Newer OS (Mojave backup to Catalina install)? No problem.

Normally, many ways around this such as boot from an OS USB Stick that you want to install but this is an iMac Pro from the Refurb Store and comes with High Sierra — my backups are Mojave.

Because I've not set up the new machine, it doesn't have an Admin password. The T2 chip prevents one from changing the security settings to allow the later OS until that is set up. Cloning is out since you can't boot from an external without changing the settings.

My choices included setting up a new User Account in HS first, update to Mojave, then use MA to restore… or set up the new account, then going into the Repair Partition to change Security to allow boot from an external, boot from a Mojave… there are a couple of others, all time consuming.

Well, I booted with ⌘ r held down and entered the Repair Partition. Among the choices was Restore from Time Machine — ok… I clicked on it just in case… Huh???

Unlike the normal Restore… menu that uses Migration Assistant, this let me chose any TM volume I want (as long as supported by the firmware) and after clicking through the erase/overwrite warning, the restore began. It's about halfway through, now.

Since I knew that my old iMP would no longer be here before this one arrived, I had disconnected my externals and ran a TM backup over Thunderbolt to a 2TB SSD to save time during the Restore. When I have finished Setup, I'll reconnect everything and let this machine inherit my old TM backups.

[mikehalloran]

Update: after the TM Restore, it flashed the spinning globe and countdown clock showing it was in Internet Recovery Mode. After awhile, it asked for the startup disk so I selected my 10.4.6 volume, the only choice, then hit Restart. It then showed the spinning globe again…

Eventually, it showed a message saying that, for the drive to boot, an update had to be run. I hit Ok… Well, many restarts and progress bars later, it finally finished and I'm good.

[HCMarkus]

NIce! Good info MIke.