To use any of these key combinations, press and hold the keys immediately after pressing the power button to turn on your Mac, or after your Mac begins to restart. Keep holding until the described behavior occurs.

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• Command (⌘)-R: Start up from the built-in macOS Recovery system. Or use Option-Command-R or Shift-Option-Command-R to start up from macOS Recovery over the Internet. macOS Recovery installs different versions of macOS, depending on the key combination you use while starting up. If your Mac is using a firmware password, you're prompted to enter the password.
  
• Option (⌥) or Alt: Start up to Startup Manager, which allows you to choose other available startup disks or volumes. If your Mac is using a firmware password, you're prompted to enter the password.
  
• Option-Command-P-R:Reset NVRAM or PRAM. If your Mac is using a firmware password, it ignores this key combination or starts up from macOS Recovery.
• Shift (⇧): Start up in safe mode. Disabled when using a firmware password.
• D: Start up to the Apple Diagnostics utility. Or use Option-Dto start up to this utility over the Internet. Disabled when using a firmware password.
• N: Start up from a NetBoot server, if your Mac supports network startup volumes. To use the default boot image on the server, hold down Option-N instead. Disabled when using a firmware password.
• Command-S: Start up in single-user mode. Disabled in macOS Mojave or later, or when using a firmware password.
• T: Start up in target disk mode. Disabled when using a firmware password.
• Command-V: Start up in verbose mode. Disabled when using a firmware password.
• Eject (⏏) or F12 or mouse button or trackpad button: Eject removable media, such as an optical disc. Disabled when using a firmware password.

If a key combination doesn't work

If a key combination doesn't work at startup, one of these these solutions might help:

• Be sure to press and hold all keys in the combination together, not one at a time.
• Shut down your Mac. Then press the power button to turn on your Mac. Then press and hold the keys as your Mac starts up.
• Wait a few seconds before pressing the keys, to give your Mac more time to recognize the keyboard as it starts up. Some keyboards have a light that flashes briefly at startup, indicating that the keyboard is recognized and ready for use.
• If you're using a wireless keyboard, plug it into your Mac, if possible. Or use your built-in keyboard or a wired keyboard. If you're using a keyboard made for a PC, such as a keyboard with a Windows logo, try a keyboard made for Mac.
• If you're using Boot Camp to start up from Microsoft Windows, set Startup Disk preferences to start up from macOS instead. Then shut down or restart and try again.

Remember that some key combinations are disabled when your Mac is using a firmware password.

Learn more

• Learn what to do if your Mac doesn't turn on.
• Learn about Mac keyboard shortcuts that you can use after your Mac has started up.

Disk Utility can find and repair errors related to the formatting and directory structure of a Mac disk. Errors can lead to unexpected behavior when using your Mac, and significant errors might even prevent your Mac from starting up completely.

Before proceeding, make sure that you have a current backup of your Mac, in case you need to recover damaged files or Disk Utility finds errors that it can't repair.

Open Disk Utility

Start up from macOS Recovery, then select Disk Utility from the Utilities window. Click Continue.
If you're not repairing the disk your Mac started up from, you don't need to start up from macOS Recovery: just open Disk Utility from the Utilities folder of your Applications folder.

Locate your disk in Disk Utility

Choose View > Show All Devices (if available) from the menu bar or toolbar in Disk Utility.

The sidebar in Disk Utility should now show each available disk or other storage device, beginning with your startup disk. And beneath each disk you should see any containers and volumes on that disk. Don't see your disk?

In this example, the startup disk (APPLE HDD) has one container and two volumes (Macintosh HD, Macintosh HD - Data). Your disk might not have a container, and it might have a different number of volumes.

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Repair volumes, then containers, then disks

For each disk that you're repairing, start by selecting the last volume on that disk, then click the First Aid button or tab.

In this example, the last volume on the disk is Macintosh HD - Data.

Click Run to begin checking the selected volume for errors.

• If there is no Run button, click the Repair Disk button instead.
• If the button is dimmed and you can't click it, skip this step for the item you selected, and continue to the next item.
• If you're asked for a password to unlock the disk, enter your administrator password.

After Disk Utility is done checking the volume, select the next item above it in the sidebar, then run First Aid again. Keep moving up the list, running First Aid for each volume on the disk, then each container on the disk, then finally the disk itself.

In this example, the repair order is Macintosh HD - Data, then Macintosh HD, then Container disk2, then APPLE HDD.

If Disk Utility found errors that it can't repair

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If Disk Utility found errors that it could not repair, use Disk Utility to erase (format) your disk.

If your disk doesn't appear in Disk Utility

If Disk Utility can't see your disk, it also can't see any containers or volumes on that disk. In that case, follow these steps:

1. Shut down your Mac, then unplug all nonessential devices from your Mac.
2. If you're repairing an external drive, make sure that it's connected directly to your Mac using a cable that you know is good. Then turn the drive off and back on.
3. If your disk still doesn't appear in Disk Utility, your disk or Mac might need service. If you need help, please contact Apple Support.