Need to downgrade my OS - What is the correct procedure?

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Need to downgrade my OS - What is the correct procedure?

I just got a "new" iMac, 2017 vintage, through OWC. It came loaded with Big Sur. But I need to downgrade the OS to High Sierra so I can run some older software.

I would like to partition the drive into two parts; one for High Sierra and the other for Big Sur; or Monterrey if that would be a better option, I'd love to hear opinions on this. I just want to have a newer OS as well as High Sierra, to run newer software that High Sierra cannot handle.

I have a Time Machine backup of my last iMac that I'd like to install in the new machine.

What is the procedure to do this? On my last iMac (2013) as I remember it was very straightforward, but in that case I already had High Sierra in the computer so I created a second partition and installed Mojave there, then installed newer software separately.

Can I partition the drive, leave Big Sur in one part and then load my Time Machine backup using Migration Assistant into the second partition? If so, do I first erase the partition where I want to put my backup? It has been too long since I did the partiton on my old iMac and I don't remember the procedure. Or am I completely screwed up and need to approach this in a different manner entirely?

Thanks in advance for any help you can give me. This forum has been a lifesaver, there always seems to be people here who know how to solve my problems and are willing to help.

iMac 27″, macOS 10.15

Posted on Dec 20, 2022 9:40 PM

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Answer 1

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Jack-19

Level 8

46,182 points

Dec 20, 2022 11:12 PM in response to tomellis

Thanks for the explanation. Based on your needs for this new iMac, I think the best way is to configure the volumes you need, macOS High Sierra and Ventura/Monterey, by first installing macOS High Sierra. Once macOS High Sierra is installed, you can add an APFS volume to your SSD, and install macOS Ventura, the latest version of macOS.

I've found it is best to first install the older version of macOS since Apple has designed modern macOS installers to support running from old versions of macOS, but not old versions of macOS Recovery interfacing with modern versions of macOS for tasks such as adding volumes, then installing to them.

Step 1: Create a macOS High Sierra installer, erase your disk, install macOS High Sierra, and migrate your data

First, create a macOS High Sierra bootable installer: Create a bootable installer for macOS - Apple Support. You will need a USB flash drive or other secondary volume with at least 14GB of available storage, formatted as Mac OS Extended.

After following the steps in the Apple Support article for downloading macOS High Sierra and using the Terminal to create the install media, follow these steps to startup from it, erase your Mac, and install macOS High Sierra:

Plug the bootable installer into your Mac that is connected to the internet and compatible with the version of macOS you're installing. (A bootable installer doesn't download macOS from the internet, but it does require an internet connection to get firmware and other information specific to the Mac model.)
Turn off your Mac.
Turn on your Mac, then immediately press and hold the Option (Alt) key.
Release the Option key when you see a dark screen showing your bootable volumes.
Select the volume containing the bootable installer. Then click the onscreen arrow or press Return.
Choose your language, if prompted.
Select Disk Utility from the Utilities window, then click Continue.
In Disk Utility, select View > Show All Devices. Select the top entry in Disk Utility titled "APPLE SSD...".
Click Erase, and make sure the information matches:
1. Name: Macintosh HD
2. Format: APFS
3. Scheme: GUID Partition Map
Click Erase, and quit Disk Utility.
Select Install macOS from the Utilities window, then click Continue and follow the onscreen instructions.

After installing macOS High Sierra, follow the prompts in Setup Assistant. When asked how you want to transfer your information, select the option to transfer from a Mac, Time Machine backup, or startup disk. Then click Continue. Connect your Time Machine drive, select your Time Machine backup, then click Continue. Continue to follow the steps to restore. Large transfers might need several hours to complete.

At this point, your new iMac should be running macOS High Sierra, with all your data restored.

Step 2: Add an APFS volume to your startup disk, and install macOS Ventura

After macOS High Sierra has been installed with your data migrated, you can add an APFS volume and install macOS Ventura, the latest version of macOS.

To start, follow the steps here, Use more than one version of macOS on a Mac - Apple Support, to add an APFS volume. Next, download macOS Ventura (or Monterey, if preferred): How to download macOS - Apple Support. When the installer opens and you're asked to choose where to install, click Show All Disks, then select the new APFS volume before continuing the install.

After your Mac restarts to the new version of macOS, follow the prompts in Setup Assistant. At this time, you can also restore data to this APFS volume, if you wish.

Jack

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Answer 2

Jack-19

Level 8

46,182 points

Dec 22, 2022 7:35 PM in response to tomellis

Glad you're up and running!

But I found that for some reason (probably I did something incorrectly) the current volume file system is not APFS, but Mac OS Extended (journaled). I did some reading and it looks like I can change the formatting to APFS, with a small chance of losing my data and having to go through the Time Machine routine again. Or I can just do what I did on my old machine and set up another partition for Ventura.

You did nothing wrong. Since your old Mac had a Fusion Drive, and therefore it was using Mac OS Extended and not APFS, the restore took your new SSD drive to Mac OS Extended.

There really isn't any problem using Mac OS Extended (Journaled) with macOS High Sierra. Instead of adding an APFS volume for Ventura, you need to partition your disk for an APFS volume.

But if you'd really like High Sierra to be running from an APFS formatted volume, you could create a new (correct) backup of the current state of your system, erase your disk, reinstall macOS High Sierra, and restore (again) using Migration Assistant during Setup Assistant (like your first attempt), not in Recovery mode like you just did since that will put the file system back to Mac OS Extended.

Or, you can keep it on Mac OS Extended, and make a new APFS volume for Ventura. To do this, navigate to Disk Utility, and select View > Show All Devices. Select the top-level entry titled "APPLE SSD...", click "Partition", and add a new partition by choosing a name, size, and format.

Jack

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Answer 3

Jack-19

Level 8

46,182 points

Dec 22, 2022 12:46 AM in response to Jack-19

I apologize for giving incorrect advice. You are correct; in macOS High Sierra, unlike macOS Ventura, you cannot select a specific backup to restore from.

However, as it turns out, you can restore from a specific backup if you restore from macOS Recovery mode. To do this, follow these steps:

Turn off your Mac.
Turn on your Mac, then immediately press and hold Command-R.
Choose your language, if prompted.
Select "Restore from Time Machine", and click Continue.
Select your Time Machine drive as the restore source, and click Continue.
Select the specific backup you'd like to recover from.
Select your destination drive, which should be titled Macintosh HD.
Follow the prompts to erase your disk, and let Time Machine restore.

I hope this helps.

Jack

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Answer 4

rkaufmann87

Level 10

148,452 points

Dec 20, 2022 11:23 PM in response to tomellis

It cannot be done, your 2017 never shipped with Mac OS High Sierra. Macs cannot have OS installed that came out before the machine was sold. The oldest OS you can run on a 2017 is the original version of Mac OS that it originally shipped with, this was likely Big Sur. What you may be able to do is to install virtualization software such as Parallels and install on the virtual partition.

As for your older software, please consider either upgrading or replacing it with apps that will run on current versions of Mac OS.

Good luck!

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Answer 5

Jack-19

Level 8

46,182 points

Dec 20, 2022 11:29 PM in response to rkaufmann87

rkaufmann87 wrote:

It cannot be done, your 2017 never shipped with Mac OS High Sierra. Macs cannot have OS installed that came out before the machine was sold. The oldest OS you can run on a 2017 is the original version of Mac OS that it originally shipped with, this was likely Big Sur.

The 2017 iMac series was originally launched running macOS Sierra 10.12.x. On Intel Mac computers, you can install any version of macOS that Apple has ever supported on that Mac.

For example, my iMac (21.5-inch, Late 2015) originally shipped, from Apple, running macOS Sierra 10.12.x, but I partitioned my startup disk and installed OS X El Capitan for older applications. I was able to do this because the 2015 iMac series originally launched running OS X El Capitan 10.11.x.

Jack

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Answer 6

tomellis Author

Level 1

5 points

Dec 20, 2022 10:19 PM in response to Jack-19

Hi Jack, thanks for answering! I got the SSD on the new iMac. If I am understanding you correctly, my Time Maching backup was created in High Sierra. That is where I have a bunch of Adobe Creative Suite software (among others) that I paid a bundle to own, and really do not want to get rid of and be forced to "rent" the newer versions.

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Answer 7

tomellis Author

Level 1

5 points

Dec 21, 2022 9:00 AM in response to rkaufmann87

Thanks to both of you! Before opting for the 2017 I did quite a bit of research to make sure running High Sierra was possible. I would have loved to move up to something newer, but this was the last model that would run High Sierra.

Jack, thanks so much for the detailed instructions. I need to go buy a new flsh drive, the only ones I have are older and I'm sure would be very slow. But with any luck I'll have things well underway later today. I'll report back if I have any issues, or when I have success with the install of High Sierra.

For the newer OS I will install on a separate partition, you seem to be a fan of going with the newer versions. Are you running Monterrey or Ventura on your 2015? I ask because for whatever reason OWC shipped me this computer running Big Sur, and I wasn't sure if there was some reason they did that rather than a newer OS.

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Answer 8

Jack-19

Level 8

46,182 points

Dec 21, 2022 2:41 PM in response to tomellis

For the newer OS I will install on a separate partition, you seem to be a fan of going with the newer versions. Are you running Monterrey or Ventura on your 2015? I ask because for whatever reason OWC shipped me this computer running Big Sur, and I wasn't sure if there was some reason they did that rather than a newer OS.

My iMac (21.5-inch, Late 2015) isn't compatible with macOS Ventura. Its currently running macOS Monterey, its latest supported version of macOS, with an OS X El Capitan volume for older software.

I am running macOS Ventura on my new MacBook Air (M2, 2022) without any issues.

Jack

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Answer 9

tomellis Author

Level 1

5 points

Dec 21, 2022 9:16 PM in response to Jack-19

Hi Jack, here is the update. I had no problem creating the High Sierra installer, erasing the hard drive, and loading High Sierra. Next I loaded my Time Machine backup, which seemed to go fine.

But then I discovered a problem, not in the directions you gave me but with something I think I did several months ago. After the computer started with my Time Machine backup I found that none of my software had been transferred, as well as all of my personal photos and my music library. Just not there, which I thought was really strange but figured I must have made a mistake when doing the Time Machine transfer.

So I first looked at the contents of the backup. The applications, photos and music were not there either. Which was very weird but at least explained why they had not been transferred. I went back through the Time Machine backups and finally found a couple of backups from June that had the missing items. I then looked at Time Machine in System Preferences because I had a suspicion of what had happened. Sure enough, in my Time Machine the Applications, Personal Photos and Music had all been excluded from backups. I am not really sure how that happened, but what matters is that it did. And I have no idea how to fix it.

When I was getting ready to transfer my data using a Time Machine backup I was not given the option to use anything other than the newest backup. Is there a way that I can chose an older backup that has the missing items? Or can I drag folders from an older backup into the most recent backup and reload?

I am pretty sure that I have another older Time Machine backup with all of the missing items on another hard drive. But I'm afraid that I will be losing a lot of data there that is on the newer backups.

I hope you have some ideas how to fix this. I'm not going to try anything until I hear back from you, since I might only manage to make things worse. :-(

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Answer 10

Jack-19

Level 8

46,182 points

Dec 21, 2022 10:57 PM in response to tomellis

tomellis wrote:

I am planning to pull it tomorrow and put in into a dock to see if the drive is functional.

I was able to find your previous thread with your EtreCheck report from a few weeks ago. Since your old iMac had a Fusion Drive, even if the hard disk was still functional (which it looks like it was failing, based on the report), since it was part of a Fusion setup, the data may not even be accessible.

Time Machine should have kept weekly backups for all previous months. Try to pinpoint exactly when Time Machine stopped making correct backups. Then, try to migrate again by using the Migration Assistant app (located in Applications > Utilities).

Once Migration Assistant is open, click the exposure triangle next to the Time Machine backup shown in Migration Assistant.

Using this interface, you should be able to scroll down and choose to restore from a backup before Time Machine stopped backing up properly.

Jack

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Answer 11

Jack-19

Level 8

46,182 points

Dec 21, 2022 11:54 PM in response to tomellis

tomellis wrote:

I never got the triangle to allow me to see/choose other backups. Just a picture of the drive with the backup, saying "most recent". No way to select another option.

I'd try again. It may take a moment to appear as it loads backups.

Jack

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Answer 12

tomellis Author

Level 1

5 points

Dec 22, 2022 5:34 PM in response to Jack-19

Hi Jack,

Good news! I was able to use the instructions you gave me to get the older copy of my hard drive installed. YAY!!! Thanks so much, losing all those apps would have been a real problem. I also found that I can replace the data that I lost by having to use an older version of my hard drive very easily using newer Time Machine backups to restore specific folders and files. It will take a little time to figure out just what needs to be replaced but that's no big deal and can be done as I discover holes.

Next I looked at setting up another volume for Ventura. But I found that for some reason (probably I did something incorrectly) the current volume file system is not APFS, but Mac OS Extended (journaled). I did some reading and it looks like I can change the formatting to APFS, with a small chance of losing my data and having to go through the Time Machine routine again. Or I can just do what I did on my old machine and set up another partition for Ventura.

What is your advice on this? From what I have read APFS looks pretty cool, but what is advertised is not necessarily how it works in reality. Your thoughts?

Thanks again for your help! I am excited that I have a working computer again, and am very curious to find out how much better its performance is that its predecessor.

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Answer 13

tomellis Author

Level 1

5 points

Dec 23, 2022 1:02 PM in response to Jack-19

Jack, it looks like the new machine is successfully set up with both partitions working. I ended up installing Monterey in the second partition. I'm having some issues with some of my software not wanting to open in the Monterey partition, which is annoying but hopefully I'll get that working again soon. Might have to reload the software?

At any rate, thanks again very much for your help. If I had tried this without help I might have eventually gotten there, but I'd hate to think how long it might have taken and the number of mistakes I could have made on the way. You're the best!

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