If you don't reinstall macOS, your Mac might start up to a flashing question mark (?).

If you want your Mac to be able to start up from this volume again, choose Reinstall macOS from the Utilities window, then follow the onscreen instructions to reinstall macOS on the volume.

When done, quit Disk Utility to return to the Utilities window.

You might be prompted to enter your Apple ID. Disk Utility shows the recommended Mac format by default.

Format: Choose either APFS or Mac OS Extended (Journaled) to format as a Mac volume.

Name: Enter a name that you want the volume to have after you erase it, such as Macintosh HD.Click the Erase button or tab, then complete these items:.After deleting any Data volumes, select Macintosh HD in the sidebar.Do not click Delete Volume Group. Do the same to delete other volumes you might have on your startup disk-except the volume named Macintosh HD. When you're asked to confirm, click the Delete button. Then choose Edit > Delete APFS Volume from the menu bar, or click the delete volume button (–) in the Disk Utility toolbar. Look for a ”Data” volume with the same name, such as ”Macintosh HD - Data.” If you have such a volume, select it.The volume representing your startup disk is Macintosh HD, unless you renamed it. Make sure that the sidebar in Disk Utility shows the name of your startup disk.Select Disk Utility from the Utilities window in macOS Recovery.By default it's the disk built into your Mac, named Macintosh HD. If you're selling, giving away, or trading in your Mac, you should erase your startup disk.

Your startup disk is the disk (volume) that your Mac started up from. Proceed based on whether you're erasing your startup disk or some other disk. Before continuing, make sure that you have a backup of any files that you want to keep. Use Disk Utility to erase (format) a hard disk, SSD, flash drive, or other storage device.Įrasing a disk or volume permanently deletes all of its files.

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