Recovering with Recovery HD
If you see a prohibitory sign (top left in Figure 20-1), spinning-disc cursor (top right), or kernel panic alert (the text in four languages that appears below the other two images) that doesn’t go away when you start up your Mac, the first thing to do is attempt to repair hidden damage to your hard drive with the Disk Utility program’s First Aid feature. And to do that, you’ll have to boot from the Recovery HD partition. That’s because you can’t run Disk Utility’s First Aid feature on the current startup disk.
To start up from this magical disk (actually, a disk partition), here’s what to do:
1. Restart your Mac.
2. Press and hold +R until you see the Apple logo.
If your Mac doesn’t boot from the Recovery HD after Step 2, hold down the Option key while booting to display the built-in Startup Manager (see Figure 20-2).
If you press Option after the startup chime instead of +R, the built-in Startup Manager appears. From this screen, you can click the Recovery HD icon (see Figure 20-2), and then click the arrow below it or press Enter or Return to boot from it. Or, if you’re going to boot from a disk other than the Recovery HD, you can select it here.