• Jul 02, 2020 How to erase your disk. Start up from macOS Recovery. Then select Disk Utility from the Utilities window and click Continue. If you're not erasing the disk your Mac. Choose View Show All Devices from the menu bar in Disk Utility. The sidebar now shows your disks (devices) and any containers.
• But formatting a drive so that it can be used as your Mac’s startup drive requires a slightly different procedure than formatting it for use as a secondary drive for storing data. Step 1: Make a.

If you've encountered a problem with macOS, the solution might be to reinstall the system on your Mac. This can be done by any Mac owner, but it can be a little bit complicated. You'll need to put your Mac into macOS Recovery, which gives you tools to diagnose problems on your Mac, as well as reinstall the operating system.

Here's how to reinstall macOS using Recovery mode.

Entering macOS Recovery

macOS Recovery has tools at its disposal that allow you to diagnose problems with your Mac's hard drive, reinstall macOS, and restore from a Time Machine backup. You can enter Recovery by pressing certain key combinations. The combination you choose will determine which version of macOS will be installed on your system when you select Reinstall macOS.

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• Press Command - R to install the latest version of macOS that was installed on your Mac without installing a later version.
• Press Options - Command - R to upgrade to the latest version of macOS that's compatible with your Mac.
• Press Shift - Option - Command - R to install the version of macOS that came with your Mac, or the version closest to it that's still available.

How to check your startup disk with Disk Utility in macOS Recovery mode

The first thing you'll want to do is make sure your Mac's startup disk is healthy. You'll need to use Disk Utility to do that.

1. Click Disk Utility when in macOS Recovery.
2. Click Continue.
3. Click on your Mac's startup drive in the Disk Utility sidebar. It should be the drive at the top of the sidebar if there are multiple drives.
4. Click First Aid.
5. Click Run. First Aid will run, checking the health of your Mac's drive. This process could take a little while.
6. Click Done.
7. Click Disk Utility in the Menu bar.
8. Click Quit Disk Utility.

How to erase your startup disk in macOS Recovery mode

If you need to start completely fresh, then you'll want to erase your startup disk using Disk Utility. If you want the content on your Mac to stay intact, skip to the next section.

1. Click on your startup disk in the Disk Utility sidebar.
2. Click Erase.
3. Click the Format drop-down menu.
4. Click on the format you want to use for your drive. If you're running macOS High Sierra or later on a Mac with an SSD, your choices will be some form of APFS.
5. Click Erase. Your drive will proceed to be erased.

How to reinstall macOS while in Recovery mode

The next step is to reinstall macOS.

1. Click Reinstall macOS.
2. Click Continue.
3. Click Continue.
4. Click Agree.
5. Click Agree.
6. Click on the drive on which you wish to install macOS.
7. Enter your Apple ID and password if you're asked to, though you might not be.
8. Click Install.

Your Mac will now go through the normal macOS installation process, eventually restarting. If you're starting from scratch, you'll need to set up your Mac from scratch.

Questions?

If you have any more questions about reinstalling macOS on your Mac, let us know in the comments.

Updated December 2019: Everything is up to date through macOS Catalina.

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Reinstall from macOS Recovery

macOS Recovery makes it easy to reinstall the Mac operating system, even if you need to erase your startup disk first. All you need is a connection to the Internet. If a wireless network is available, you can choose it from the Wi-Fi menu , which is also available in macOS Recovery.

1. Start up from macOS Recovery

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To start up from macOS Recovery, turn on your Mac and immediately press and hold one of the following sets of keys on your keyboard. Release the keys when you see an Apple logo, spinning globe, or other startup screen.

Command (⌘)-R

Reinstall the latest macOS that was installed on your Mac (recommended).

Option-⌘-R

Upgrade to the latest macOS that is compatible with your Mac.

Shift-Option-⌘-R

Reinstall the macOS that came with your Mac, or the closest version still available.

You might be prompted to enter a password, such as a firmware password or the password of a user who is an administrator of this Mac. Enter the requested password to continue.

When you see the utilities window, you have started up from macOS Recovery.

2. Decide whether to erase (format) your disk

You probably don't need to erase, unless you're selling, trading in, or giving away your Mac, or you have an issue that requires you to erase. If you need to erase before installing macOS, select Disk Utility from the Utilities window, then click Continue. Learn more about when and how to erase.

3. Install macOS

When you're ready to reinstall macOS, choose Reinstall macOS from the Utilities window. Then click Continue and follow the onscreen instructions. You will be asked to choose a disk on which to install.

• If the installer asks to unlock your disk, enter the password you use to log in to your Mac.
• If the installer doesn't see your disk, or it says that it can't install on your computer or volume, you might need to erase your disk first.
• If the installer is for a different version of macOS than you expected, learn about macOS Recovery exceptions.
• If the installer offers you the choice between installing on Macintosh HD or Macintosh HD - Data, choose Macintosh HD.

Please allow installation to complete without putting your Mac to sleep or closing its lid. During installation, your Mac might restart and show a progress bar several times, and the screen might be empty for minutes at a time.

If your Mac restarts to a setup assistant, but you're selling, trading in, or giving away your Mac, press Command-Q to quit the assistant without completing setup. Then click Shut Down. When the new owner starts up the Mac, they can use their own information to complete setup.

macOS Recovery exceptions

The version of macOS offered by macOS Recovery might vary in some cases:

• If macOS Sierra 10.12.4 or later has never been installed on this Mac, Option-Command-R installs the macOS that came with your Mac, or the closest version still available. And Shift-Option-Command-R isn't available.
• If you erased your entire disk instead of just the startup volume on that disk, macOS Recovery might offer only the macOS that came with your Mac, or the closest version still available. You can upgrade to a later version afterward.
• If your Mac has the Apple T2 Security Chip and you never installed a macOS update, Option-Command-R installs the latest macOS that was installed on your Mac.
• If you just had your Mac logic board replaced during a repair, macOS Recovery might offer only the latest macOS that is compatible with your Mac.

If you can't get macOS Recovery to offer the installer you want, you might be able to use one of the other ways to install macOS.

Other ways to install macOS

• You can also install macOS from the App Store or Software Update preferences. If you can't install macOS Catalina, you might be able to install an earlier macOS, such as macOS Mojave, High Sierra, Sierra, El Capitan, or Yosemite.
• Or create a bootable installer disk, then use that disk to install macOS on your Mac or another Mac.