I'm having some problems with entering sleep and wakening, so I'm considering making a fresh installation of Mountain Lion. How can I make a fresh install of ML? I have Bootcamp partition which I'd like to remove also.

Also, what is the procedure for fresh Lion install?(maybe I'll try installing this OS because in Lion I didn't have this problem).

BTW - I have ML downloaded through Apple Store because I bought the new laptop and I'm entitled for upgrading.


3 Answers 3


A clean reinstall of Mountain Lion involves creating a bootable USB stick from the installer downloaded from the App Store. You would then boot from it by holding ALT (Option) while rebooting. When you boot into the USB stick, use Disk Utility to delete both the Lion and Windows partitions from your drive.

As for clean reinstalling Lion, since it came pre-installed, you would have to backup your hard drive and 'erase' it which would then prompt you to reinstall the OS.

  • Thank you, I followed these steps, though I didn't remove the Bootcamp partition. Very happy result as it fixed my sleep-wakening problems.
    – Anonymous
    Commented Jul 30, 2012 at 8:12
  • 1
    Glad to help. :)
    – Bo A
    Commented Jul 30, 2012 at 8:33

Or, if you have working (bootable) OS X on external (USB) Hdd, simply:

  • Time Machine!!! (Don't forget backup) :)
  • download ML from Appstore
  • after the download it start the installation
  • quit it
  • move the downloaded mountain installation app from /Applications into the external HDD
  • reboot mac
  • hold down ALT and boot the external USB
  • if want you can repartition the internal HDD with Disk utility.app (remember, you're booted from external HDD, so, want repartition the internal one...)
  • run the copied installation app
  • select your internal HDD as target
  • install
  • done

I'we done installation this way because i'm changed my HDD into SSD, so I used my old internal HDD as bootable external HDD...


If you are going to remove your Windows partition, you could also do the following :

  1. Remove the Windows partition using Disk Utility.
  2. Create a new hfs+ partition in its place.
  3. Use Superduper or CarbonCopyCloner to backup your Lion install to new partition.
  4. Boot the backup.
  5. Erase the original Lion partition
  6. Install Mountain Lion on the newly erased partition
  7. When you've verified Mountain Lion works as expected, remove remaining Lion partition and grow Mountain Lon filesystem to full disk size.

You could skip steps 3,4,5 and just install Mountain Lion on the second partition but the advantage of doing it this way is that the OS files will be on the first partition, at the beginning of the disk which is most performant.

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