MacOS – Clean Lion install, keeping Time Machine history

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I have a 2011 unibody MacBook Pro, and have been gathering kludge on it for some time, and on previous machines (2007 MacBook Pro, 2004 Powerbook) whose data I've migrated over using the Migration Assitant. I'd like to, at some point soon, do a fresh install of Lion, grab my data from backup (or a disk image clone), and reinstall my applications (only the ones I'm currently using, with no detritus from other apps I've installed, used, and since uninstalled).

However, I use a Time Capsule (1 TB) for backups, and wanted to know two things:

  1. Is it possible, after doing the install, to have the previous history of my computer (on the Time Capsule) integrated with my current and future Time Machine backups? (I.e., the Time Capsule sees the new, clean machine as the same machine, and allows me to step into my file history and grab stuff, if need be.)
  2. If the answer to the above question is yes, how would I do this?

Apologies in advance if this question has been answered elsewhere. A cursory perusal of the Q&A here didn't turn up anything; but I know there's the chance I could have missed something.

Best Answer

I think you'd be better off doing a clean install and using Setup Assistant to copy over just the users and settings. (Setup Assistant, like Migration Assistant, can use a Time Machine backup as the source. The are basically the same application, but Setup Assistant configures your Mac for the first time and Migration Assistant helps you copy stuff over to a Mac you've already set up. You can only use Setup Assistant immediately after a clean install of the OS, which of course includes the first time you boot up a new Mac.) That way for sure your new users will have the same UID and UUID as your current users, meaning your backup and all your other drives ownership and read/write permissions will still work as before, and there's a chance that the Time Machine interface will work to fetch old files. I wouldn't bet on the latter, but I've had permissions problems before when not migrating users. Of course, this might be different if all your machines only have one user; my machines have 3.

I'm pretty sure, also, that if Time Machine doesn't work straight off the bat, you can trick it into working by replacing the com.apple.TimeMachine.MachineID.plist file in the Time Capsule's sparsebundle disk image for the backup for the machine in question. But that's a bit advanced and certainly unsupported, so I'd leave that for "when all else fails".

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