OS X Lion: Reinstall Mac OS X

Reinstall Mac OS X

Under some circumstances, you may need to reinstall Mac OS X. You can reinstall Mac OS X while keeping your files and user settings intact.

Important: You need to be connected to the Internet to reinstall Mac OS X.
  1. Choose Apple menu > Restart, and then hold down the Command (⌘) and R keys while the computer restarts.
  2. If you’re not connected to the Internet, choose a network from the Wi-Fi menu in the right corner of the menu bar (in the top-right corner of the screen).
  3. Select Reinstall Mac OS X, and then click Continue.
  4. Follow the onscreen instructions. In the pane where you select a disk, select your current Mac OS X disk (in most cases, it is the only one available).
  5. To start the installation, click Install.

Mac OS X Lion comes with a built-in recovery disk that you can use to reinstall Mac OS X, repair a disk, restore from a Time Machine backup, and more. To use the recovery disk, restart your computer while holding down the Command (⌘) and R keys. If you want, you can also create an external recovery disk. For more information, see this Apple Support article:

OS X Lion: About Lion Recovery Disk Assistant