Downgrade from Catalina to Mojave from BEFORE machine's manufacture date...

[Beliblis]

Hi,

I received my brand new MacMini yesterday, running Catalina of course. For software/driver reasons (mainly my trusted old Wacom tablet), I want to downgrade to Mojave.
I got my external drive set up as an installer drive with Mojave on it. It appears in the "Startup Disk" selector, but I can't select it because "The bless tool was unable to set the current boot disk.".

I've been working on Mac OS for over a decade, and this is not my first system downgrade. But it is the first time I'm trying to go "older system than shipping system".
So I'm guessing this is probably because Catalina was already out when my Mac was manufactured, right?

If so: Is there a way around this? (I remember installing Adobe CS6 on High Sierra was officially not possible, but I found a way around it).

Many thanks for your help!

 

[casperes1996]

As far as I know, as long as the model itself, not the manufacturing, existed when the OS you want to install was still the latest, so it has drivers, it should be OK.
If you hold the Option key on boot up you can't pick it either?

What do you get if you run the bless command manually as root?

 

[Beliblis]

You're right... I had an old hard-drive with Mojave lying around (which I had used as a test system on my old 2012 MacMini), and I could successfully use that as a startup disk on the 2018 MacMini.
But I still can't select the new SSD with the Mojave Installer. Still a "bless tool" problem... (from within Mojave itself I mean).

I did some research, and came across some forum posts saying it could be the SSD (enclosure/manufacturer/firmware) that causes the problem. But in my case, this can't be the case: I already had Catalina installed on the very same external SSD. Only after I noticed that the new Wacom drivers don't support my tablet, I now decided to downgrade to Mojave.

Could it be that a Mojave boot drive isn't compatible with that m2 SSD, whilst Catalina is? That'd be really weird...

Option Key on boot up doesn't do anything.
How do I run the bless command manually? I mean what'd be the terminal command?

 

[casperes1996]

Could it be that a Mojave boot drive isn't compatible with that m2 SSD, whilst Catalina is? That'd be really weird...

Seems unlikely.

Option Key on boot up doesn't do anything.

In what way does it do nothing? Is there no drive other than main drive to pick or did you not get into the boot picker at all? I assume you did hold the option key down throughout the booting process until presented with the boot picker, yes?

How do I run the bless command manually? I mean what'd be the terminal command?

from the manual page:

FOLDER MODE


To bless a volume with only Mac OS X or Darwin, and create the BootX and boot.efi files as needed:





bless --folder "/Volumes/Mac OS X/System/Library/CoreServices" --bootinfo --bootefi





MOUNT MODE


To set a volume containing either Mac OS 9 and Mac OS X to be the active volume:





bless --mount "/Volumes/Mac OS" --setBoot


Do both. Obviously replace "Mac OS [X]" with the name of the volume.

Place sudo in front of each command to run as root.

For further reference you can view the manual yourself by typing man bless.
"man [command]" works for anything

 

[Beliblis]

I fixed the problem, albeit a bit of a cumbersome procedure:
I used Carbon Copy Cloner to clone Mojave from my old drive to the new m2 SSD. This allowed me to select the m2 drive as a boot drive (via System Preferences).

Very strange that the 'proper' way didn't work. (Just for reference: this is the procedure I followed, which DIDN'T allow me to select the m2 as a boot drive: https://support.apple.com/en-us/HT201372

Once Mojave was working from the m2 drive, I did a few more restarts after installing some software/extensions. The boot procedure is still a bit hit-and-miss and recognising the external boot drive seems to take longer than on my old 2012 MacMini.

 

[macnicol]

Interesting, just how did you get your MacMini that came with Mac OS Catalina installed to boot from Mac OS Mojave disk? Wth my 2019 iMac that came with Catalina installed, I've tried that several times and different ways using external boot HDs and USB flash drives with NO success.