Installing Mojave over Big Sur

I just bought a new Mini, with the idea that I’d pass my existing one to my wife, who would then be able to use a new, larger, display (her current one dates from 2007 and is failing).

I want to stick with Mojave, however, as I don’t want to add going to Big Sur while developing with Xojo as another potential problem area just now. So I thought I might just replace the Big Sur install with Mojave, but this just fails at a number of steps.

Has anyone done this successfully?

Is your new Mini intel?

Yes, sorry, I should have said - yes it is.

start the mac holding Shift + Option + Command + R until a globe appear
(you should use a wired ethernet instead of a wifi if possible)
this will boot at apple servers and let you format and install the first macos allowed to boot on this mac. if you have an actual mac mini intel it should be Mojave.

source : https://www.macworld.co.uk/how-to/mac-recovery-mode-3674052/

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That only offers Big Sur. I was in fact at the recovery page earlier: here’s what I posted on UseNet (the uk.comp.sys.mac newsgroup):

I obtained the Mojave installer from the AppStore, so that should be OK. I put the installer on an external SSD, but trying to run that under Big Sur just gives the message that it doesn’t run under Big Sur. So I installed Mojave on the external SSD using another Mini. That part worked OK. But when I tried to use that as a startup disk, I soon got into the security hole that startup from an external device was not allowed.

Next thing was that Big Sur got pissy about my password. I could login but the p/w was refused for unlocking any SystemPrefs pane, even though User&Groups said I was an Admin user who could “manage this machine”. I got round this by re-installing Big Sur - over the Internet. Then the p/w was OK again, I could turn off the no-booting-from-external-device security.

I made the SSD into a bootable Mojave installer using instructions I found on MacWorld. That then showed up as a selectable startup device, but on booting it, it then said that “macOS needs reinstalling on this device”.

So far it’s looking as if Apple is locking out any chance to install Mojave instead of Big Sur.

(I have a laptop running Big Sur, I could look to see what the Recovery Page offers there).

This part, at least, is a security setting that you can change while booted into Recovery.

1- There is a way, you will have to google for that, to create a thumb drive that will be used to install a version of MacOS, in your case that would be Mohave.

2- Use a key combination to boot into disk utilities (it called that way ?), once done erase the hard disk.

3- Then another key combination will let you install MacOS for a source you specify, that will will be your thumb drive.

I never got why Apple used un key combination per utility, instead on using one that would bring a menu and let you choose what utility you need.

It was my understanding that any machine coming with Catalina or newer from Apple could not be downgraded to anything older than Catalina.

In fact a Mac set to have a minimum version that can be installed. Maybe the OP will have to keep the old mini and give the new one to his wife :roll_eyes:.

The minimum version it can run is the one it shipped with. Best he can do would be to install and run Mojave on a virtual machine.

Speaking of which, has anybody tried setting up a Mojave virtual machine on an M1 based machine? Guess I could just try it – I have an M1 mini and a Parallels license…

This is what I have known since the mid-nineties, but I have seen others claim that you can install the OS from when the machine was first on sale. So if this is the same model number as a Mac Mini from 3 years ago, it might work. However I have not tried.

I haven’t tried, but I don’t know if it would be possible due to the differences in CPU architecture and that Parallels is virtualization and not emulation, it might work if Parallels can run under Rosetta, but my gut tells me this not likely as Rosetta is not an emulator, but a translator.

A quick web search suggests this was not possible as recently as March 2021, at least according to this blog.

While virtualization like Parallels may not be possible, perhaps it is possible via QEMU. Instructions for doing that with Catalina are here and may work with older macOS versions as well. One would presume the faster the hardware, the better this may work. So we’ll soon see what the specs of the new M1X/M2/whatever are beyond more cores.

Tsck…

Duckduckgo is your friend :slight_smile:

https://duckduckgo.com/?q=how+to+downgrade+macos&ia=web

TimStreater said it is an Intel machine…

According to wikipedia, what you want to do is not possible:

Your Mac Mini model:

Installed macOS:

Mojave it not supported by that hardware.

Your tests leads to that conclusion.

Both my existing mini (running Mojave) and the new one (running Big Sur) describe themselves as Mac mini (2018). They have the same model id: Macmini8,1

It’s possible that:

  1. Running earlier than Big Sur is forbidden by a change to the firmware or boot rom since I bought my 2018 model (in 2018 - at which time it was running earlier than Mojave as I upgraded to that).

  2. The OS installer phones Apple and discovers that the machine with this serial number was supplied with Big Sur, and therefore forbids a downgrade.

  3. The OS installer looks on the internal drive and discovers Big Sur there - downgrade forbidden.

I’ll try prevent (2) and (3).

EDIT: The boot rom version is the same on both machines.

On your Mac mini running Mojave can you create a MacOS installer USB drive ( How to create a bootable installer for macOS - Apple Support ), then you’d boot to recovery on the new Mac mini, open Disk utilities, wipe the disk and format as hfs+j. Then reboot using the usb installer drive (holding down option).

Yes, I already did this (although I got the instructions - same as from your link, from MacWorld). What I omitted to do was to erase the target disk before trying the install, so I’m about to pursue that now.

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