How to erase and reinstall OS X on your Mac

With some new Mac hardware on the horizon, lots of folks will be replacing their existing machines with brand new gear. And some of them will be giving their existing machines to other folks. If that’s you, take a read of the linked Apple support article. This is the officially sanctioned way to erase and reinstall OS X.

The instructions show you how to erase your hard drive using Disk Utility (you can even do the DoD-approved wipe your drive 7 times method), then use OS X’s built-in recovery disk to reinstall OS X on the wiped drive.

Needless to say, be sure to back up your hard drive before you even read the instructions.



  • Robert Davey

    Does the recovery partition get upgraded at OS upgrade time? e.g. If I bought a MacBook with Snow Leopard, used the Mac App Store to update to Mountain Lion, and then reinstalled the OS, is the newly installed OS Snow Leopard or Mountain Lion?

    • Dave Mark

      An excellent question. Not sure. But I think this is designed for Mountain Lion and above.

    • noliv

      Yes, the recovery partition is upgraded at OS upgrade. On the linked page, click the link at the bottom about recovery partitions : the second note on the bottom of that page implies that the recovery partition is upgraded at OS upgrade time. (I didn’t try as I destroyed my recovery partition by doing a custom Fusion Drive with unsupported hardware… Non-Apple Fusion Drive are not ‘partitionnable’)

  • Moeskido

    Thanks for this. I’m not planning on replacing my Mac Pro, but I’m certainly overdue for a nuke and pave. Biggest annoyance: deactivating and reinstalling registered software like Adobe CS.

  • Sigivald

    you can even do the DoD-approved wipe your drive 7 times method

    An erase is an excellent idea, if the person you’re selling the machine to isn’t personally trusted.

    The “seven times” thing, while a DoD requirement, is purest overkill with hardware that isn’t from the mid 90s or earlier.

    (See Guttman’s epilogue on his own 1996 paper, especially “Any modern drive will most likely be a hopeless task“, speaking of recovering from even a single overwrite pass.)