How to upgrade from an older Mac operating system to macOS Catalina or Big Sur

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.

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.

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

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 Other 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.

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.

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

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.

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.

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