Need to reinstall the operating system on your Mac? You can do it in just a few steps using macOS Recovery. Before you start, make sure you have access to an internet connection, that your Mac is plugged into power, and that it’s turned off. If you’re using a wireless keyboard, plug it into your Mac if possible or use a wired keyboard or your built-in keyboard.
To start up in macOS Recovery, you’ll need to choose one of three combinations on your keyboard as soon as you turn on your Mac.
macOS Recovery Options
Command-R will reinstall the latest version of macOS that was installed on your Mac. In most cases, this is Apple’s recommendation. Option-Command-R will upgrade your macOS to the latest version that’s compatible with your device. Shift-Option-Command-R will reinstall the version of macOS that came with your Mac or the closest version still available. Let’s choose Command-R. Once you know which key combination you need, turn on your Mac and immediately press and hold the keys until you see an Apple logo. Then release them.
You may also see a spinning globe or other startup screen if you choose a different combination. Enter the firmware password or administrator password if prompted. When you see the Utilities window, you’ll know you have successfully started up from macOS Recovery.
Choose Reinstall macOS, then click Continue and follow the onscreen instructions. Next, select the disk you want to install macOS on. During setup, the installer may ask to unlock your disk. If this happens, enter the password you use to login to your Mac. The installation process might take a while, so wait for it to complete without putting your Mac to sleep, turning it off, or closing the lid.
During installation, your Mac might restart and show a progress bar several times. Or the screen might be empty for minutes at a time. When it’s done, you’ll see a login window. Just enter your password and follow the prompts.