How to downgrade from Lion to Snow Leopard

Mac OS X Lion (s aapl) has been out for a few days now, and I’m quite happy using it on all my machines. But judging by questions I’ve been asked, that’s not a universal experience. A few folks have asked me how to go about stepping back to Snow Leopard. It’s possible, but unfortunately, you may not be able to easily take your current apps and documents with you. There’s a method that does restore your apps and settings, but you’ll need a cloned backup of your pre-Lion drive for it to work.

1. The “best fit” solution

Most won’t have a cloned backup of their drive on hand, I’m guessing. The good news is that performing a clean wipe and install is a good idea for general maintenance of your Mac. The bad news is that in this case, you really have no choice. Here’s how to save what you can and get back to Snow Leopard, provided you have a Snow Leopard install disc (including the one that came with your computer, if it’s a recent purchase). This method also erases the emergency recovery partition Lion automatically installs.

  1. Backup your User folders to an external drive. This should preserve your documents, photos, music, etc. If you store those things in locations not in the User folder, make sure to copy those over too.
  2. Insert the Snow Leopard disc. Restart your Mac and hold down C to boot to your DVD drive.
  3. Go to Utilities in the menu bar once the installer pops up and select “Disk Utility.”
  4. Find the drive in the sidebar where Lion is installed, select it and navigate to the Partition tab.
  5. Click on the drop down menu under Partition Layout and select “1 Partition.” Hit Apply.
  6. Now navigate to the Erase tab and make sure “Mac OS Extended (Journaled)” is selected, then hit Erase to delete all data on the drive.
  7. Quit Disk Utility to get back to the Snow Leopard installer and proceed with the install.
  8. Restore your User folder and documents from your backup.
  9. Run Software Update to get everything current, install your apps from your original install media and update those as well.

2. The “best case” solution

If you managed to clone your drive (Dave describes how in this recent piece) before you installed Lion, which you should do if you haven’t yet taken the plunge, then you can get everything back the way it was.

A popular option for cloning your drive is Carbon Copy Cloner, which is a handy utility to have for any Mac owner. Assuming you’ve done that, follow the directions above to get your drive primed and ready, but stop at step 6 and follow these instructions instead.

Now you’re ready to install Snow Leopard from your Carbon Copy Cloner backup. Here’s how to do it:

  1. Attach the drive containing your CCC clone to your Mac.
  2. Open System Preferences, then go to the Startup Disk preference pane.
  3. Chose your CCC external drive as the startup disk.
  4. Restart and launch CCC, then choose your backup from the “source” menu.
  5. Select your Mac’s internal drive as the destination.
  6. Chose “Restore items from a backup” from the settings pop-up menu and hit the “Clone” button.
As with any major software change, it’s a good idea to have a dependable cloning strategy in place in case you want to revert. But it’s also been my experience that it’s never the end of the world if you have to just do a clean wipe and reinstall, especially if you consistently backup your data from the beginning. Users not yet sure about Lion might consider installing it on a separate partition first to make sure they like it before using it as their primary system.