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A very nice feature of TimeMachine is the possibility to configure a new Mac automatically. Nevertheless, when you switch from OS 10.6 to OS 10.8 using TimeMachine during installation, there are a lot of files that are not needed anymore in 10.8. Unfortunately, the setup does not recognize this and I have to remove them manually. Is there a possibility to remove all system files that are only needed for < 10.8 automatically?

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If you document what files are no longer needed, we might be able to make a more narrow answer. – bmike Nov 5 '12 at 18:04

I'm pretty sure there is no such thing. But you do have a couple of options.

  1. Get another totally clean installation of 10.8 and diff your whole filesystem. Then decide upon each "extra" file if it needed by you or your applications.
  2. The "easy" option. Do a clean 10.8 installation and then restore from time machine into a folder on your desktop (f.ex.). Then manually copy over the files and stuff you want to keep
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Time Machine used to have a built-in option to disable backing up all "System Files" so I would use that to make one last backup so that when you restore, the system won't be inclined to migrate any of those system files over.

If you no longer have the original Mac to make a new smaller backup, you may not even need this since that setting was removed on Mountain Lion.

I have not seen any need for this sort of cleaning in practice, but it can't hurt things. Are you seeing space issues or thousands of files being migrated? This is an area where I've felt OS X does quite well in not restoring un-needed content so it's not something most people do to clean their Macs at this point.

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