With WWDC almost upon us, the imminent first beta-release of what’s expected to be macOS 12, and 11.5 also in beta, many are now wondering how best to install these, or even macOS 11.5 when it’s released. How should you prepare for the possibility that any of these could prove a lemon? How can you upgrade while retaining the ability to roll back to your current macOS?
The traditional trick of cloning your current internal storage to an external disk, so that you can clone it back if you need to roll back macOS, should still work on an Intel Mac, but is likely to fail on an M1 model, leaving it stuck and dysfunctional until Apple provides an update which isn’t so flawed. This article suggests some ways out.
Don’t install betas at all
The golden rule of beta-testing is that you should never even consider installing any beta-release on a production system, using only systems which you can afford to have fail. The snag at the moment is that many need to test on both Intel and M1 Macs, and relatively few have spare Macs covering both architectures. That may force you to compromise, which is what the rest of this article is about.
One important consideration before deciding to press ahead and upgrade an Intel Mac you can’t do without is firmware. Although you can roll back macOS, you can’t install older firmware. The only exception to this is for a Mac with a T2 chip: you can then use Apple Configurator 2 to update the firmware in the T2, and erase recoveryOS and macOS on the Mac’s internal storage. Before considering this, install Configurator 2 and study its Help book. You’ll need a Mac running macOS 10.15.6 or later, a USB-C to USB-C charge (not data) cable, and of course a second Mac.
Don’t install the upgrade on your internal disk
For M1 Macs in particular, this should be a good choice, and is how I do all my summer beta-testing each year. This still carries a risk, in that your Mac may install a flawed firmware update. You can reverse that if it has a T2 chip or an M1 SoC, as I mentioned above, but for a plain Intel Mac the only recovery would be a subsequent firmware update which could be tricky or even impossible to install. So there remains a small risk of disaster.
The procedure for installing macOS on an external disk attached to an M1 Mac runs:
- Connect the disk to an available port on your M1 Mac, which could (subject to its compatibility) include a dock or hub.
- Format the disk using Disk Utility. If it has been previously formatted using an older version of macOS, I recommend re-formatting it with 11.4 or later if possible. At this stage you can divide it into containers for multiple versions of macOS if you wish.
- Run the full Installer app and select that external disk as the destination.
- Towards the end of the installation process, the installer may claim there’s “about a minute remaining” for many minutes. Give it time!
- Once installed, the Mac will start up in the newly installed macOS for you to configure it in the usual way.
As you’d then expect, you can switch between booting from the internal and external disks using the Startup Disk pane or in Recovery mode.
If you must install the upgrade on your internal disk
The best approach to work out what you need, is to consider how you’d recover your Mac in the event that the upgrade caused a serious problem.
For an Intel Mac, you need a bootable external disk containing your previous macOS, together with its data, which could if necessary be provided from a Time Machine backup, for instance. There is a twist here for Intel Macs with a T2 chip, though: you’ll need to enter Recovery Mode and ensure that Startup Security Utility is set to allow booting from external media, as Apple explains here. Without that, your Mac won’t be able to boot from the recovery disk which you’ve prepared for it.
Once your Intel Mac has started up from that external disk, you can then decide how best to return its internal disk to a stable state, which could include cloning the external disk back to internal storage, or installing a fresh copy of a more stable version of macOS and restoring/migrating from your backup.
For an M1 Mac, because it can always boot from a suitable external disk, you might think that all you need is a bootable external disk. While that might get your Mac up and running again, it can’t be cloned back to the internal disk, so complete recovery is going to be more complicated. In any case, that can’t restore a previous version of macOS to the internal storage, nor can it address any problems arising from a firmware upgrade – which may include its Recovery system.
The cleanest and quickest way to roll an M1 back to a previous macOS complete with its firmware is to perform a full restore using Apple Configurator 2. To do that, you’ll need another Mac running at least macOS 10.15.6, Apple Configurator 2 (free from the App Store), a USB-C to USB-C charge (not data) cable, and the restore image, an IPSW file of around 13 GB. Configurator can download the latest IPSW for you, or you can obtain that or older from Apple, via Mr Macintosh’s listing.
The procedure is detailed in Configurator’s Help book, and in this article. Once your M1 Mac has been successfully restored, you then configure it as if it was a new M1 Mac. That gives you the opportunity to migrate your data from your backup, or cloned Data volume.
It may instead be possible to simply install the current or previous release of macOS on your M1’s internal storage.
To re-install the current release, it’s simplest to enter Recovery mode and use the main Options menu. This may even preserve your existing Data volume in the new bootable volume group it creates. Otherwise you’ll need to migrate from your previous backup or clone. For an older release, you’ll need its full Installer app, but might find that can’t be installed on your internal SSD, in which case you’ll have to use Configurator to perform a restore from the appropriate IPSW file.
None of these solutions uses any clone or copy of the current System volume. Thus, there’s no point in trying to clone the System volume from your internal storage, as it’s simply a waste of space. Instead, ensure that you have at least two faithful copies or backups of the Data volume – something which is easy using Time Machine, Carbon Copy Cloner, and/or SuperDuper!
Whatever you do
Finally, whatever you decide to do, don’t make snap decisions to change your plan and end up putting your Mac at risk. Some betas don’t install reliably on certain media or configurations. If that prevents you from putting your plan to install that macOS on an external disk, don’t install it on your internal disk without making proper provision for any problems. The chances are the next beta will address those problems.
Never rush into testing any pre-release software. Think the consequences through carefully and protect your Mac from disaster.