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How Do I Reformat My Mac?

Hi, I am having some problems related to corrupt system software on my 13″ 2012 MacBook Pro running OS X 10.8.2, and I would like to re-format it to factory settings. I have OS X Mountain Lion on my “Purchases” list on the Mac App Store. Some websites instruct me to create a “bootable backup” using this, however I do not know whether that is legal and is safe to do so. Other sites instruct me to download a “InstallESD.pkg” file in the MT Lion installer. Please advise.

Comments: 5 Responses to “How Do I Reformat My Mac?”

    11 years ago

    First, realize that this is a drastic step. What makes you think that you have "corrupt system software?" How did you come to that diagnosis?
    I'm asking because usually someone that could be sure they have "corrupt system software" would also know how to reformat their Mac. So perhaps you have an issue, like something isn't working right, and there is a better way to fix it other than nuking the OS. Have you gone to the Genius Bar or an equivalent to have it checked out?
    Second, before you do anything else, do you have a good backup? Are you backing up with Time Machine? If not, do that now. Trouble means that you might be about to lose everything. And even if you aren't, you are going to want to backup before restoring the system.
    Maybe consider making a second backup too, a clone using Carbon Copy Cloner or SuperDuper, just incase.
    To re-install the OS, you don't need to do something like making a bootable backup or downloading some special hacked installer. You simply need to reboot into your recovery partition.
    Apple has all the info at
    It is as simple as restarting with Command+R held down.
    I wouldn't try to erase the drive at first. Instead, simply choose to re-install Mountain Lion. If the problem real is that the OS is somehow damaged, then this will fix it. No need to erase all of your files and applications.

      11 years ago

      First of all, thanks for the the rapid response, Gary.

      I have had numerous problems with my mac, of which some are listed here:

      - Finder stops responding, doesn't restart when force restarted
      - Mac frequently hangs (screen freezes, doesn't respond to user input)
      - Every disk connected to my mac would unmount, as seen in Disk Utility
      - Launching Launchpad would cause ALL my apps to start, causing the system to reboot.
      - The Finder would
      - Turning on Airdrop would cause my mac to restart
      - Launchpad would jumble up my apps' order at every system restart

      Actually, I went to an Apple Authorised Service Provider and they told me I had to reformat the OS, claiming "corrupt Mac OS". Before doing anything, I'd just like some advice for this. I have two Time Machine backups, of which both I keep up to date.

      One more question, If I re-install the OS, would I lose iLife '11, and all my applications?

        11 years ago

        I would definitely first just re-install OS X. Don't reformat the drive, just re-install the OS. This won't affect your documents or apps, so it is much easier.
        If you do eventually reformat, then restoring from your TM backup should give you back all of your apps and documents too. But it is a longer process.
        Your iLife apps, and anything you get from the Mac App Store are safe because you can always re-download your Mac App Store purchases (those apps are considered purchases, even though you got them with your new Mac).
        Report back here with what actions you took and how they worked, and any problems you ran into, if you can. Restoring in this manner is still quite new and others can certainly use more information from people that have done it.

          11 years ago

          Well, I tried re-installing OS X, exactly as described in the Apple support document and, it worked! Thanks Gary! It seems that applications called "SystemUIServer", "mdworker", and "KernelEventAgent" which caused the problem, according to the guy at the Genius Bar. However, I have run into another issue since the re-install.

          All apps I attempt to download through the Mac App Store fail to install and warn me that "App XYZ failed to download, please use the purchases page to try again." Any ideas?

            11 years ago

            Just try again. Perhaps sign out of your account and sign in again in the App Store app first.

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