Many people remember Mac OS X 10.6.8 fondly. Not just 10.6 Snow Leopard, but particularly its very mature 10.6.8 release, the final one in that series. It’s considered a stable and perfectly fine version. It’s not a problem—until they want to mitgrate to a newer computer with the same files, preferences, users, and other elements as their current one. That’s particularly true when they want to keep their system and essentially brain transplant it to the latest two updates, macOS Catalina and Big Sur, and find there’s no direct path.

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Apple offers Migration Assistant both when setting up a Mac (whether new or erased) and as an app within macOS, particularly to migrate user accounts and applications. As a source, you can use a Time Machine backup, a disk image copy of your macOS startup volume (via a cloning app, for instance), or another Mac.

1. To create a bootable Mac drive you need any disk with Mac OS X 10.11.0 El Capitan or newer (10.12 Sierra, 10.13 High Sierra, 10.14 Mojave, up to 10.15 (Catalina) either running as your main system, or just being installed on a drive that's connected to your Mac at the moment.
2. The Mac Startup Manager will update as needed, so if you add or remove bootable drives or devices on your Mac, the list will automatically display the current options.
3. The fix is to open the Startup Disk preference pane and set the startup disk correctly for your Mac. Reset NVRAM and SMC: The NVRAM and SMC hold information used by your Mac during startup. If either becomes corrupt, it can cause unusual effects on your Mac.

But Migration Assistant has its limits: in Catalina and Big Sur, you must migrate from a backup made from or a computer running Mac OS X 10.11 El Capitan or later. Attempts to copy from older installations lead to an error.

However, you’re not stuck. You have several alternatives you can try.

Upgrade past 10.6.8

If you can’t make changes, unlock your disk by pressing the padlock icon in the lower-left corner and enter your Administrator Password; Tap the + symbol; Add the App or Terminal to your approved apps with Full Access. If you didn’t close the app previously, close the app now if it’s already running and then add it to the list for full. Once that’s done, plug in your Unibeast USB drive in your computer, and then restart your computer. Boot into Mac OS X Yosemite Installer. Restart your Hackintosh, and plug in your Mac OS X Yosemite Installer USB drive. If things go well, your computer will boot from the USB drive instead of booting from your normal hard disk.

It may seem like a pain, but if you have a computer that can be upgraded to 10.11 El Capitan or later, that’s your best bet. This list of models from One World Computing will help you figure out if your Mac can be upgraded that far. It covers years of Mac releases. (No Macs that can run Snow Leopard can be upgraded to Catalina or Big Sur, which would solve the problem, too.)

Apple has instructions on installing a terminal release of Mac OS X or macOS for its old computers.

How To Repair The Startup Disk On A Mac

Once upgraded to El Capitan or later, you can then run Migration Assistant to transfer data to Catalina or Big Sur.

If your computer’s last OS option isn’t El Capitan, read on.

This Disk Cannot Be Used To Startup Your Computer Catalina Drive

Copy just the user directory

When spanning such a long gap between releases, you may not need applications or any settings files—you just want to transfer all your document, pictures, and other personal files. In that case, you can use these directions in a Mac 911 column from last year. While that article was written to help you overcome a Migration Assistant failure, it also works when Migration Assistant can’t.

Each of the techniques in that article lets you move the files you need over to a new Mac. The options vary by what your older system is capable of and the level of technical detail you want to cope with.

Install an older Mac OS on an external drive for migration

Can't Get To Disk Utility On Mac Startup

If the Mac you’re upgrading to (not from) is in the right range of vintages, you can do the following:

1. Install Mac OS X 10.11 El Capitan on an external drive. (Download El Capitan from Apple’s site.) El Capitan seems to be the last release that can migrate files from Snow Leopard.
2. Use the Startup Disk preference pane to select that external drive and restart.
3. Use Migration Assistant during setup or after setting up on the external drive to transfer data from your Snow Leopard Mac.
4. Use Startup Disk to restart with your newer Mac’s intended startup volume.
5. Now run Migration Assistant pointing to the external drive.

Can't Change Startup Disk On Mac

If you don’t own a Mac that can install El Capitan, you might be able to borrow such a machine from someone and use the same external drive approach that won’t affect the startup drive of their system.

This Mac 911 article is in response to a question submitted by Macworld reader Balthasar.

Ask Mac 911

We’ve compiled a list of the questions we get asked most frequently along with answers and links to columns: read our super FAQ to see if your question is covered. If not, we’re always looking for new problems to solve! Email yours to mac911@macworld.comincluding screen captures as appropriate, and whether you want your full name used. Not every question will be answered, we don’t reply to email, and we cannot provide direct troubleshooting advice.