OS X: How to erase and install
You can use OS X Recovery to erase your computer using Disk Utility and then reinstall OS X.
Normally you don't need to erase your disk to reinstall OS X. The OS X Installer is designed to allow you to perform an install in place if you are troubleshooting. If you need to erase your disk because you are transferring your computer to a new owner, you can use Disk Utility to erase the disk before reinstalling.
Important: Before you erase and reinstall, back up your essential files. If you’re installing on a notebook computer, make sure your power adapter is connected and plugged in.
Use these steps if you need to erase a disk before installing OS X:
- Before you begin, you need to be connected to the Internet.
- Choose Apple menu > Restart, and then hold down the Command (⌘) and R keys while the computer restarts.
- Select “Disk Utility,” and then click Continue.
- Select your startup disk from the list on the left, and then click the Erase tab.
- From the Format pop-up menu, select Mac OS Extended (Journaled), type a name for your disk, and then click Erase.
- After the disk has been erased, choose Disk Utility > Quit Disk Utility.
- 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).
- Select Reinstall Mac OS X, click Continue, and then follow the instructions.
OS X includes a built-in Recovery system that you can use to reinstall Mac OS X, repair a disk, restore from a Time Machine backup, and more. To use the recovery system, restart your computer while holding down the Command (⌘) and R keys. If you want, you can also install OS X on an external drive, or create an external recovery disk.