macOS Reversion: How to Downgrade from BigSur

macOS Reversion: How to Downgrade from BigSur

macOS BigSur has a great deal going for it, with lots of new features, new security and privacy safeguards, as well as new apps such as News and Home. But even with all of these new capabilities, a few of you may find yourselves wishing you could go back to one of the previous versions of the Mac operating system.

Maybe BigSur is just performing poorly on your system, or perhaps one of your favourite or critical apps hasn’t yet been updated for BigSur and you simply need to downgrade the OS to be able to keep running an older app.

Whatever the reason, you can downgrade from macOS and revert to an earlier version by following these steps:

How to Downgrade From macOS BigSur
You should always start this process with a backup. This will ensure that, if something should go wrong, you can recover your data and start again without having lost anything. Another reason you need the backup is that the process of downgrading includes erasing the start-up drive from your Mac. The backup may be the only place you can find documents and files should you need to restore them. We recommend creating a clone of your start-up drive to make accessing those backup files as simple as possible. You can also use Time Machine but whichever method you use you should ensure you have a backup before going ahead.

Before you start the downgrade process you should consider these alternatives:

  • If the reason you are downgrading is that you need a specific app that doesn’t work well under BigSur, you could install an older version of the macOS on a separate drive or partition. Allowing you to keep BigSur and switch between the OS versions as required.
  • Another option would be to use a virtualisation app, like Parallels where you can run an earlier version of the macOS. This will let you run earlier versions of apps that you may need, without having the need for a downgrade.

If downgrading is what you need to do, then there are three ways you can do it:

  • Use a downloaded Mac OS installer for the version you want to revert to.
  • Use Time Machine.
  • Use Apple’s recovery service to reinstall the original version of the Mac OS which your Mac shipped with.

Choose your method based on your needs and the availability of an installer for the OS you want to return to.

Mac Operating System Installers
One of the most simple choices is downgrading to macOS Mojave since the installer app is still available in Apple's App Store. You can find it using the direct link:

If you want to go back to an earlier version of the OS, you’ll need to have downloaded the installer before you upgraded to BigSur, or have access to a Mac running an earlier version of the operating system, and then log in to the App Store and download the installer you need using the store’s Purchased tab. Once the installer has finished downloading, quit the installer which may start automatically.

Screen Shot 2019 10 07 at 2 47 51 PM

NB: Mojave can currently be found in the Mac App Store using the link above, but Apple may choose to remove or restrict the download in the future.

When you have the installer downloaded, make a bootable copy of the installer on a USB flash drive or other media. One option is to use the DiskMaker X app and follow the instructions in Create a Bootable macOS Mojave Install Drive with DiskMaker X.

APFS Issues When Downgrading
Since Mojave your machine upgrades the startup drive to APFS, Apple’s new File System. APFS is currently only fully supported on all media types in Mojave and BigSur. It’s important to note that High Sierra can support APFS on SSDs but not Fusion or hard drives. Sierra does have experimental support for APFS,  but trying to use APFS with Sierra may not be advisable.

The reason for mentioning APFS is because when you downgrade it may be worth converting your startup drive back to HFS+ to ensure compatibility during the install process. Converting to HFS+ will completely erase the startup drive.

Use Internet Recovery to Downgrade
Use Apple’s Internet Recovery system to erase and reformat the APFS startup drive to an HFS+ formatted drive. It’s possible to use the normal Recovery volume, as long as it’s located on a different volume than your startup drive, but it is much easier to use Internet Recovery and not have to worry about the location, or the version of the Recovery volume.

Erase and Reformat the Startup Drive
Warning: This process will completely erase your Mac’s startup drive!

This section covers the basics of erasing and reformatting the startup drive. You will need an Internet connection.

Using Disk Utility, included with the Internet Recovery option, you can erase and reformat the startup drive.

  • Shut down your Mac.
  • Start your Mac whilst holding the Option + Command + R keys down. Continue holding the three key combinations until you see the spinning world globe and the text “Internet Recovery.”
  • In the macOS utility window, select Disk Utility and click or tap the Continue button.
  • You will be in the Disk Utility window. Select Show All Devices from the View menu, or the View button on the toolbar.
  • In the sidebar, select the startup drive - not the volume or container.
  • Now click or tap the Erase button in the toolbar.
  • In the sheet which drops down, select Mac OS Extended (Journaled) as the Format option and GUID Partition Map as the Scheme.
  • Bow click or tap the Erase button.
  • Quit Disk Utility.

Install an Earlier Version of the Mac OS
First complete all of the steps in the “Erase and Reformat the Startup Drive” section above and continue from here.

  • Connect the bootable installer you made earlier to your Mac.
  • Restart your Mac whilst holding down the option key.
  • Boot manager will display a list of drives to start up from. Select the bootable installer you created.

It may take a while to boot but the installer will start and then take you through the installation process for the version of the Mac operating system that you are downgrading to.

Alternative: Downgrade Using Time Machine
It is possible to use Time Machine to restore your Mac back to the OS it was running before you upgraded to macOS BigSur. In order for this method to work, you must have a Time Machine backup which was made before you upgraded to Mojave.

Warning: Restoring from Time Machine will erase the contents of your Mac’s startup drive!

When selecting the backup to use, make sure the macOS version listed is for the OS you want to return to.

For reference:  BigSur   10.15 = Catalina   10.14 = Mojave   10.13 = High Sierra

As before, follow the instructions in the “Erase and Reformat the Startup Drive” section above. Once you have quit Disk Utility pick up the steps here:

  • Ensure your Time Machine drive is connected to your Mac.
  • The macOS utilities window will open, select “Restore from Time Machine Backup” and click or tap the Continue button.
  • The Restore from Time Machine window will open with a few warning messages. Just click or tap the Continue button to proceed.
  • A list of available restore sources will show. Select the drive you use for your Time Machine backups and click or tap the Continue button.
  • Time Machine System Restore will list restore points available to use and each restore point will include the version of the Mac OS that was present when the backup occurred. Select a restore point that includes the version of the Mac OS you wish to use. Click or tap the Continue button.
  • Select the drive you wish to use as the destination for the Time Machine restore from the list of connected drives that appears. This should be your startup drive which you erased in a previous step. Click or tap the Restore button.
  • The restore process will then begin. Once it completes restart your Mac.

Alternative: Downgrade to Mac OS Version Originally Included with Your Mac
Since macOS Sierra 10.12.4 the Recovery volume has had a secret... it is possible to use the Recovery volume to reinstall the version of the Mac OS that shipped originally with your Mac.

Note: Apple includes a disclaimer that the original version of the OS for your Mac may no longer be available, in this case, the OS downloaded will be the next closest one that is still available.

This means that you don’t need to download or create a bootable installer. However, the OS that originally shipped may not be the one you want. If you were unable to download the installer you wanted, this may be an option for downgrading.

If you use Shift + Option + Command + R to start Internet Recovery, it is possible to return to the original OS that came with your Mac.

Warning: This process will erase your startup drive!

  • Follow the steps in the “Erase and Reformat the Startup Drive” section above. Disregard the step that tells you to start your Mac whilst holding down the Option + Command + R keys and start your Mac whilst holding down Shift + Option + Command + R instead.
  • Once your Mac starts up in Internet Recovery, just follow the remaining steps in that section. Once you quit Disk Utility you can proceed from here.
  • In the macOS Utilities window select the Reinstall macOS option, click or tap the Continue button.
  • The installer for the Mac OS will appear; follow the onscreen instructions to complete the installation.

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