Apple's strategy of making macOS updates available for free from the Mac App Store and providing access to public betas of upcoming new versions has been very successful in encouraging us to keep our Macs updated. However, sometimes enthusiasm for the newest features can get the better of us and we upgrade in haste only to repent later.
There are several possible scenarios in which you may want to reverse and downgrade to an older version of macOS (or Mac OS X). You might install a public beta of a new version of macOS, and then discover it's got bugs in it which break apps you depend on. And even when you upgrade to a new full version of the OS, you may find that features you relied on work differently or have disappeared.
Regardless of the specifics, the clear solution is to undo the update and revert to the version of macOS you were using before - but that's sometimes easier said than done. In this article we show you how to downgrade macOS. Read next: macOS Sierra vs Mac OS X El Capitan
How to remove a macOS beta
The guide below works for both beta and full release versions of macOS. But there are some slight differences to the way you will approach the situation.
That way you can test the beta while keeping your files and data safe from any bugs.
Nevertheless, if you've already installed a beta on top of your existing system, the process for reversing it is exactly the same as for a full version. Follow the instructions below to wipe your startup disk and re-install the latest full version of macOS.
Preparing to downgrade macOS
As with anything else, the key to minimising difficulty later is to prepare before you start.
The simplest way to reverse an OS update is to restore from Time Machine. So, if you're not using Time Machine to make regular backups, start now, before you upgrade.
Make sure you have a recent, complete backup of your system. That backup can be on a directly connected external disk, hooked up by USB, FireWire or Thunderbolt. Or it can be on a Time Machine compatible network drive, like Apple's Time Capsule. If you're running macOS Sierra, the network drive can use the SMB protocol; older versions of macOS only support AFP for Time Machine backups.
If you've got a Time Machine backup and need to revert to an older version of the OS, read the next section. If not, skip ahead to Downgrade without a Time Machine backup.
Restore from a Time Machine backup
Before we begin, it's important to note that when you restore from a backup, you'll wipe everything on your startup disk. That means any work you've done since you upgraded will be lost. So… back it up.
You can use Time Machine to do this, too. If you don't use Time Machine, clone your startup disk to a spare external drive or at the very least make a copy of any files you've created or modified since you upgraded. If you've got photos in the Photos app and you don't use iCloud Library, manually export them to an external disk so you can re-import them later.
Once you've backed up everything you want to keep from the newer version of the OS, restart your Mac with the Time Machine disk connected and while holding Command and R until you see the Apple logo.
When the options appear on screen, choose 'Restore From Time Machine Backup' and click Continue. Then select the Time Machine disk and select the backup you want to restore from - in most cases, it will be the most recent backup prior to installing the newer version of the OS. Follow the onscreen instructions.
If you backed up files from the newer OS using Time Machine, when your Mac restarts, click the Time Machine icon in the menu bar and select Enter Time Machine. You can now navigate to the most recent backup and the files you want and retrieve them.
If you used another tool to back up your files, use its restore facility. If you copied them manually, copy them back.
Do you have a bootable installer of the OS you want to revert to on an external disk?
If so, you can plug that in, select it as the startup disk and reboot. When your Mac has restarted, launch Disk Utilities, select the Erase tab and choose your Mac's regular startup disk (the one with the new OS on it).
When the disk has been erased, restart while holding down Command-R and select Reinstall macOS from the Utilities window and select your regular startup disk. Follow the onscreen instructions and wait for your Mac to restart.
Normally when you re-install macOS and have a backup, you'd choose the option to migrate data from the backup to the fresh installation, but in this case the backup is a later OS than the one you've just installed, so migrating data is likely to lead to compatibility problems. If, however, you have a clone of your Mac's startup drive from before you upgraded, you could migrate data from that. You'd still be without the files you created while running the newer OS, but you'd at least have a base from which to start.
You would then manually copy files created while you were running the newer OS from the backup you made before you wiped your Mac's startup disk.
How to create a bootable installer
Haven't got a bootable installer? Don't panic. You can download installers for earlier versions of macOS from the Mac App Store, provided you've installed them from there in the past.
So, for example, if you downloaded and installed macOS Sierra from the Mac App Store then installed the public beta of High Sierra and now want to revert to Sierra, you can search for Sierra on the App Store and download it.
Older versions of macOS won't appear through normal search, unfortunately, but you can find them in the Purchased section.
The important bit is that once it has downloaded, it will try to install. Don't click anything that allows the installation to proceed, just quit the installation and a copy of the OS installer will remain in your Applications folder.
You'll need to do this before you wipe your startup disk, obviously.
Here's how to download and create a bootable version of an earlier version of macOS.
Once you've created a bootable installer using the instructions on that page, you can follow the instructions above to reverse a macOS upgrade.
Fixing common problems
Reversing an upgrade carries with it a number of wrinkles and pitfalls.
Most of these are due to changes in file formats and settings between versions of the OS. So, for example, if you create a document or work on a file in a new version, whether it's a beta or full release, of macOS and then try and open it in an older version, it may not work.
To mitigate this, it's wise to export any documents you've created or worked on in the newer OS in a standard file format. So, for example, if you use Scrivener or Ulysses, export documents as RTF files. That way, if the native files don't survive the reverse upgrade, you'll be able to re-import the RTF files.
Take screenshots of preferences and settings
Whenever you perform a clean install of macOS, which is what you're doing here, it's a good idea to take screenshots of any custom settings you've created in apps or in System Preferences. That makes it easier to re-create them later.
You should also make a note of user account and password details for anything you've set up while running the new version of the OS. If you don't use iCloud or Chrome to synchronise bookmarks, it's a good idea to export those and make a copy.
And unless you're using the migrate data option outlined above, you'll also need installers and licence codes for apps you use. If those are downloads from the Mac App Store, you can just re-download them from the Purchased section in the App Store. If not, make sure you can download them from the vendor's website. If you don't use a password manager to store licence codes, make sure you've got a copy of them before you start.
If you use Dropbox, OneDrive, Google Drive or any other form of cloud storage, make sure your data is in sync before you start the process of reversing an upgrade. It's easy to forget that the files that live in your Dropbox folder, or example, are local files and that while synchronisation is frequent, the loss of an internet connection will prevent it and you could have files in your local folder that haven't yet been copied to the cloud.
Clicking on the cloud service's logo in your menu bar should tell you whether synchronisation completed successfully and files are up to date.
If you use Gmail, iCloud mail or any other IMAP server for your email, make sure it's up to date and any drafts you've composed recently have been synchronised. If you use a POP3 account you'll have to manually back up the mail database and restore it after you reverse the upgrade. Or, if you only have a few messages you need to keep, forward them to a Gmail account - you could set one up especially for that purpose.