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How do I install OS X 10.8 (Mountain Lion)?

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Upgrading from Mac OS X 10.7 (Lion) or OS X 10.6 (Snow Leopard)

Mac OS X 10.8 (Mountain Lion) is no longer available for purchase from the Mac App Store. If you have Mac OS X 10.7 (Lion) or OS X 10.6 (Snow Leopard), and your computer meets the system requirements for OS X 10.10 (Yosemite), you can upgrade directly to that version instead; see How do I install or upgrade OS X 10.10 (Yosemite)?

Reinstalling Mountain Lion

Note: To reinstall or recover Mountain Lion, you must have an active Internet connection. If you are on campus at Indiana University, UITS recommends the wired Ethernet network instead of wireless. However, if IU Secure is your only option, see In Mac OS X, how do I connect to IU Secure if I am booted from my Recovery HD?

Reinstalling while keeping files, applications, and settings

  1. Restart your computer, and immediately hold down command-r until the gray Apple logo appears.
  2. If prompted to select your main language, make a selection, and then click the arrow.
  3. Click Reinstall OS X, and then click Continue. Follow the instructions and then choose your hard disk. Click Install and enter your Apple ID information if prompted.
  4. When the installation is complete, from the Apple menu, select Software Update... and install any available updates.

Reinstalling while erasing everything on your computer

  1. Restart your computer, and immediately hold down command-r until the gray Apple logo appears.
  2. If prompted to select your main language, make a selection, and then click the arrow.
  3. Click Disk Utility, and then Continue.
  4. In Disk Utility, from the left column, click your hard disk. Select the Erase tab.
  5. Next to "Format:", make sure Mac OS Extended (Journaled) is selected. Next to "Name:", give your disk a name.
  6. If you would like to securely erase your data, click Security Options..., adjust the slider accordingly, and click OK. When you're ready, click Erase..., and then Erase again to erase your disk. When the process completes, quit Disk Utility.
  7. Click Reinstall OS X, and then Continue. Follow the instructions and then choose your hard disk. Click Install and enter your Apple ID information if prompted. Once the installation is complete, you'll be asked to enter basic information and have the option to transfer data from another computer or a backup.
  8. Select Software Update... from the Apple menu and install any available updates.

This is document bcnk in the Knowledge Base.
Last modified on 2014-11-10.

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