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How can I downgrade my OS?

I bought a refurbished 2015 MacBook so that I could continue using my legacy software, but its SSD came preinstalled with OS 10.14 Monterey. I want to degrade it to 10.12 Sierra. I have a Time Machine / bootable external HD with Sierra but can't work out how to erase the new SSD and put Sierra on it. I've tried everything, including creating a HFS partition on the SSD, but when I try to run disk utility from the external drive, it doesn't even see the SSD.

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hello info,

it's quite simple, read this before you start -

On a Mac with an Intel processor

To take advantage of these features, you must press and hold the keys immediately after you press the power button that turns on your Mac, or as soon as you start restarting it. and keep them until the described behavior occurs.

Command (⌘) + R: Boot from the built-in macOS Recovery. You can also hold down Option + Command + R or Shift + Option + Command + R to start macOS Recovery over the Internet. MacOS Recovery installs different versions of macOS depending on the key combinations you press. If your Mac is protected by a hardware password, you'll be prompted for the password.

Reinstalling macOS doesn't delete data on your Mac. To start the installation, select Reinstall macOS in the utilities window in macOS Recovery Mode, then click Next and follow the on-screen instructions.

During installation, please follow the instructions below:

  • If the installer requires you to unlock the drive, enter your Mac login password.
  • If the installer does not see the disk or prompts that it cannot install the system on the computer or volume, you may need to erase the disk first.
  • If the installer offers a choice between installing on a Macintosh HD or Macintosh HD-Data drive, select the Macintosh HD drive.
  • Create the conditions for the installation to complete without putting your Mac to sleep, shutting it down, etc. Your Mac may restart several times and show a progress bar, and the screen may be blank for several minutes.

After the installation is complete, your Mac may restart and display the setup assistant. If you are selling, replacing, or giving away your Mac, press Command + Q to exit the assistant without completing setup. Then click Disable. When the new owner starts up the Mac, they can use their own information to complete the setup.

Erase data on Mac using Disk Utility

  1. Boot into macOS Recovery: Turn on your Mac, then immediately press and hold the Command (⌘) and R keys until you see the Apple logo or another image.
  2. If you are prompted to choose a user whose password you know, enter their administrator password.
  3. In the Utilities window, select Disk Utility and click Next.
  4. Select Macintosh HD in the sidebar of Disk Utility. Can't see your Macintosh HD drive?
  5. Click the Erase button on the toolbar, then enter the required information:
    • Name: Macintosh HD
    • Format: APFS or Mac OS Extended (Journaled) depending on Disk Utility recommendations
  6. Click Erase. However, if you see the Erase Volume Group button, click that button instead.
  7. If prompted, enter your Apple ID. Forgot your Apple ID?
  8. After erasing, select any other internal volume on the sidebar, and then click the delete volume button (-) on the toolbar to delete that volume. When doing these steps, ignore all internal volumes named Macintosh HD or Macintosh HD - Data, and any volumes in the External and Disk Images sections in the sidebar.
  9. Close Disk Utility to return to the utilities window.
  10. To restart from the erased drive, select Reinstall macOS in the utilities window, click Next, and follow the on-screen instructions to reinstall macOS.

that's all.

Update (05/19/2022)

If your Macintosh HD drive is not visible in Disk Utility

The built-in startup disk is the first item listed in the Disk Utility sidebar. It's called Macintosh HD, unless it's otherwise called. If you don't see it there, choose Apple menu > Shut Down, then disconnect any unnecessary devices from your Mac and try again.

If the disk still does not appear in Disk Utility, or the disk utility reports that the wiping process has failed, your Mac may require assistance from Apple Support.

The solution may be to connect this disk to another computer (another motherboard) and check its operation (this is one of the last models from which the SSD can be removed and checked organoleptically). It is also possible that the pins on the disk port are dirty or damaged, sometimes it happens.

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Thanks, I appreciate your trying to help but. I've tried all that before posting my question. The problem is that Disk Utility does NOT see the SSD. It doesn't see it to install onto it, it doesn't see it to erase it. It's not there. And in Disk Utility there is no "view all disks" option. If you want I can send you a screen shot.

Again - I can boot from the SSD (Monterey) and I can boot from the recovery HD (Sierra). But I cannot restore Sierra onto the SSD.

da

above you have an update

da

Thanks, does that answer apply to a situation where the startup disk is indeed booting? In other words, the SSD startup disk is booting and working 100%, and it shows up in its OWN Disk Utility; it only doesn't show up when running disk utility in Recovery Mode. Does my Q make sense?

da

Yes, Dan below has a right. This is what I did on my m.Air right now. External boot disk with windows on usb (min.32GB). It sees everything, deletes everything, does not create anything good, but there is an empty space after the Apple partition. The problem seems to be solved. Try this way.

da

As I commented there, I've tried that, but the Sierra Disk Utility doesn't see the internal drive.

da

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You're fighting a file system issue! Apple altered things between Sierra (HFS+) and High Sierra (APFS) and newer.

The version of Disk Utility the different macOS's offer is what holding you back. The older Sierra Disk Utility within Internet recovery can't see the newer APFS partition. Sadly, I've never been able to get it to prep the internal drive as you need to get to the boot sectors but the Internet OS recovery still has the need of accessing your drive. Think of it this way your shoe heel broke off on your shoe, you hobble to the local shoe cobbler to have him fix your shoe (to expensive to toss) clearly he can't fix your shoe while your foot is in it can he. That's the rub here! Recovery is like your foot its still holding tight to the shoe (drive in this case).

You'll need to boot up under an external boot drive so you can fully wipe the internal drive using Disk Utility. Ideally, this should be a Sierra drive.

From the sounds of it you have a second system (your older system) if its working we can make quick work of this just by using Target Disk Mode Here's a great writeup on it Understanding the Applications for Target Disk Mode Your other means is to create a bootable disk using Internet recovery. You'll need a drive which you can wipe and is sizable enough to hold the OS (32GB or larger). then all you need to do is boot up under it get the OS Installer from here How to get old versions of macOS. One last option is just use your other system to setup an OS installer drive download the installer on your working Sierra Mac and then format a USB thumb drive with GUID Journaled file system using Disk Utility then copy the installer to it and then convert it following this guide https://support.apple.com/en-us/HT201372

I'll be honest here, I haven't tried backoff from Monterey yet so Apple could have thrown us a fast ball in altering the EFI firmware so it can't use the older OS HFS+ volumes as a boot drive.

Reference: Mac startup key combinations

Update (05/19/2022)

Make sure you select the top most level otherwise you can't erase it as I've done here

Block Image

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Thank you - I have already tried this. When I boot from the external Sierra drive, its Disk Utility doesn't see the internal drive at all (neither the APFS partition nor the HFS partition). It's completely invisible. I haven't tried Target Disk Mode but at this point have no reason to believe it would get a different result, but I'm surely willing to try!

da

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Someone on another forum found the solution to my problem, so I'm posting here in case it might help someone:

Boot to a High Sierra installer, and the internal drive will be now visible, and you can erase, or do anything else that you need to do with the internal drive. If you still need to erase the internal drive (and you do need to erase that drive to do what you want with a Sierra system!), then you have to erase the drive with a system newer than Sierra. High Sierra will be successful. Once the drive is erased (and you have reverted back to a Mac OS Extended format), then you will be able to install Sierra -- followed up with reinstalling Monterey. You will want to decide how much drive space you want for each system. I think you will also realize that you will perhaps struggle when choosing to boot from one system, then the other on the same drive. There would be workarounds to get that to work, too. If you want to have both systems, because of your legacy software, then that will be something that you will have to deal with.

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info sarà eternamente grato.
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