Tricking the Migration Assistant into migrating a user-account to an earlier OS (i.e., end-running "source contains a newer release of macos" errors)

[Minghold]

Quandary: I am happily running MacOS Mojave on a 2009 C2D Macbook Pro (via Open Core Legacy), and would like to port a painstakingly tweaked-for-years user settings and installed software to early i-series processor-equipped machines of the non-metal era. As it appears that a solution hack-enabling hardware-acceleration on non-metal Macs is not forthcoming with Mojave, my intention is move all user-account settings to the last MacOS version that ran adequately on those machines: High Sierra. Naturally, the otherwise ideal solution -- the Migration Assistant -- won't let you do that, which relegates the user to laborious reinstallation and settings tweaking of dozens of applications.

Goal: trick the Migration Assistant into importing a user-account from a newer version of the OS. (This will probably entail cloning the source OS, in this case Mojave, to a new temporary drive partition, then stripping out and/or replacing various software bits that the tool checks for. --It is not necessary that the temporary drive partition remain bootable, only that it be rendered kosher as an import source by High Sierra's Migration Assistant, and that the High Sierra destination user account successfully boot after importation. There will probably be other clean-up involved afterwards, such as too-new application versions that will need to be backpeddled, but that can wait.)

Assume possession of any required MacOS installation files, knowledge of disabling SIP and Terminal use, possession of cloning tools such as Carbon Copy Cloner 5 (if those are necessary in your ventured solution), and knowledge of proper drive preparation.

 

[Slartibart]

Using

ditto -c -k --sequesterRsrc --keepParent the-user-folder-of-interest archive-of-that-user.zip

in the terminal and then

ditto -x -k archive-of-that-user.zip destination

after copying to the new machine does not work?

Or just using Target Mode (High Sierra supports APFS) to connect and copy?

 

[Minghold]

Using

ditto -c -k --sequesterRsrc --keepParent the-user-folder-of-interest archive-of-that-user.zip

in the terminal and then

ditto -x -k archive-of-that-user.zip destination

after copying to the new machine does not work?

Please explain exactly what is occurring with these commands. TIA.

Or just using Target Mode (High Sierra supports APFS) to connect and copy?

Cloning MacOS boot partitions is not an issue (i.e., there should be no need for target mode). Porting a user-account backwards from Mojave into High Sierra is what I am trying to do. (The Mojave installation was cloned into an HFS+ partition, so the annoyances of dealing with APFS security recalcitrance is not an issue either. I just want to trick the Migration Assistant into the using a future-OS source. (The same procedure, once derived, should presumably work for any other move backwards among HFS+ partitioned MacOSes.)

 

[Slartibart]

the ditto command sequence can be used to archive e.g. the complete content of user folder - basically a .zip-archive (you can similarly use e.g. disk image for that, or rar, …) - copy that to the target system and then merge its contents with an existing user account there.

Obviously there are potential sources for problems when moving backwards like format changes in preferences-, or .plist-files, etc. - but that’s a different building site. 🤓

I have no good idea to trick the Migration Assistant to use it to transfer a user folder with all contents from newer to old - but you do not need it for that (macOS itself creates a disk image of such content if delete a user and archive it).

Digging up that previous link, disk imaging the user folder on Mojave and then mount and copy the content to the identical user on the High Sierra system seems to offer a solution.