Any ideas what this is about?

[CaptainMorgan]

I have just downgraded from Big Sur back to Mojave using a clean install but keep getting this message at boot up. All updates have been done so now running 10.14.6 and all apps and programs are running fine. Any ideas please? To avoid any confusion it is installed on my internal fusion drive.

 

[MacInWin]

When you did the clean install did you repartition and reformat the drive? Big Sur makes some changes to the drive structure that are NOT compatible with older versions of the OS. To get around the problem, you must repartition and reformat to end up with a totally empty drive to install Mojave successfully. It could be that although your install seems ok, and you can boot, that the rest of the drive that Big Sur used is not available to you unless you do the repartition/reformat/reinstall.

 

[CaptainMorgan]

When you did the clean install did you repartition and reformat the drive? Big Sur makes some changes to the drive structure that are NOT compatible with older versions of the OS. To get around the problem, you must repartition and reformat to end up with a totally empty drive to install Mojave successfully. It could be that although your install seems ok, and you can boot, that the rest of the drive that Big Sur used is not available to you unless you do the repartition/reformat/reinstall.

My drive was in 2 partitions, Mac OS Data and Recovery. I erased both partitions and reinstalled Mojave on Mac OS Data. Should I have partitioned the whole disk back to a single partition?

 

[MacInWin]

Yes. That is what I was saying you had to do to get it right.

 

[CaptainMorgan]

Yes. That is what I was saying you had to do to get it right.

Yes. That is what I was saying you had to do to get it right.

Ok thanks for that. I guess I'm in for another session of reinstalling and getting all my stuff redownloaded, or would I be able to reinstall from a time machine backup?

 

[MacInWin]

You can probably migrate from a TM backup after you the the OS install properly. When it first boots it will offer to migrate data before you get a chance to create an account. Take that offer and point to the TM drive and select what you want restored. Let it do its thing and eventually it will let you log into your account with the name username and password as before. The one thing that might make it a bit dodgy is that the backup was made with Big Sur and you are going backwards, so the migration might not work. But. it's worth a try to avoid having to reinstall everything

 

[CaptainMorgan]

You can probably migrate from a TM backup after you the the OS install properly. When it first boots it will offer to migrate data before you get a chance to create an account. Take that offer and point to the TM drive and select what you want restored. Let it do its thing and eventually it will let you log into your account with the name username and password as before. The one thing that might make it a bit dodgy is that the backup was made with Big Sur and you are going backwards, so the migration might not work. But. it's worth a try to avoid having to reinstall everything

Thanks for that Jake, I will see how I go. I think maybe I will reinstall everything, at least then I will know there should be no Big Sur fragments left behind.

 

[Rod]

Assuming you are going to use Disk Utility to erase your drive you must erase the drive media itself. The item at the top of the list and you must ensure you unmount Macintosh HD and Macintosh HD_Data first.

 

[CaptainMorgan]

Assuming you are going to use Disk Utility to erase your drive you must erase the drive media itself. The item at the top of the list and you must ensure you unmount Macintosh HD and Macintosh HD_Data first.

Thats where I have been going wrong, I have been erasing the Mac OS and Mac Data partitions instead of the full disk without unmounting the other partitions. Pretty much stuck here in lockdown, nothing on tv worth watching today, so a good time to get it all sorted. Thanks so much for your input.

 

[Rod]

I'm sure you'll get it this time, you obviously got the rest of the process nailed, When formatting the drive media you have to choose the additional Partition Mapping option, choose GUID. You can name it anything but to avoid confusion down the line I'd stick to Macintosh HD and format as APFS.

Just out of curiosity why are going back from Big Sur to Mojave?

 

[CaptainMorgan]

I'm sure you'll get it this time, you obviously got the rest of the process nailed, When formatting the drive media you have to choose the additional Partition Mapping option, choose GUID. You can name it anything but to avoid confusion down the line I'd stick to Macintosh HD and format as APFS.

Just out of curiosity why are going back from Big Sur to Mojave?

I'm sure you'll get it this time, you obviously got the rest of the process nailed, When formatting the drive media you have to choose the additional Partition Mapping option, choose GUID. You can name it anything but to avoid confusion down the line I'd stick to Macintosh HD and format as APFS.

Just out of curiosity why are going back from Big Sur to Mojave?
[/QUOTE

Truth is Rod I have a couple of 32bit apps that I still want to use and I just get the feeling that with Big Sur I am no longer in control. Apple wants to poke its nose in at every opportunity (even more than usual lol) I never really got on with Catalina and I just feel comfortable with Mojave and it seems to run better on my iMac.
I now have everything reinstalled and all seems to be running fine.

 

[Rod]

Well done, it's been a particularly problematic (more than usual) task to revert from Big Sur for those that have chosen to do so for whatever reason.
Apple have made a lot of changes recently, removing support for 32bit apps and towards the introduction of their new M1 processor, improving OS security and incorporating iOS apps into macOS with the result that many feel a bit overwhelmed with all the differences.

 

[ferrarr]

I believe that Apple going to their chips, will make Macs, exactly the same as all their other devices. Once you upgrade, you can't go back.

 

[michaelakern]

Glad to see you got everything working again