How to reinstall macOS Catalina/Mojave/High Sierra on your Mac?

By Vivian | Posted to Howto on July 3rd, 2020 |

Summary: This page is about how to reinstall macOS in macOS Recovery mode. Based on if you want to keep the original data on the startup disk, you can either choose to clean reinstall macOS or to reinstall macOS without data loss.

Reinstalling macOS gives your Mac a fresh start especially when you are frequently bothered by some issues, such as Mac not booting up, Mac hanging on the beach ball, apps frozen your Mac, or slow performance. Most of the time, such issue results from some system-level problems, while reinstalling macOS can easily save your life.

How to reinstall macOS from macOS Recovery mode?

When you need to reinstall macOS on your Mac, macOS Recovery mode makes this process easy and quick.

Step 1: Make sure your Mac is connected to a stable Internet within all the following steps.

Step 2: Restart your Mac and immediately do one of the following.

  • Press and hold Command + Option + R.This allows you to reinstall the latest version of macOS that is compatible with your Mac computer from the internet.
  • Press and hold Shift + Command + Option + R. This option allows you to reinstall the macOS that came with your Mac, or the closest version still available.
  • Press and hold Command + R. This allows you to reinstall the version of macOS stored on your built-in recovery disk, including any updates that you installed.

Step 3: Release these keys when you see an Apple logo, spinning globe, or the Utilities window.

macOS Recovery mode

Step 4: Enter the requested password if you are prompted to enter a firmware password or the administrator's login password.

Step 5: Decide if you want to clean install the system, or just reinstall macOS without losing your original data.

If you want to factory reset the Mac for selling or giveaway, or the startup disk becomes corrupted, you might want to erase the startup disk before reinstallation. This guarantees a fresh and clean installation as it wipes all your personal data on the disk.

How to factory reset your Mac?

If you only want to reinstall macOS because the original operating system is not working as you expect, you might want to keep your personal data intact. In case files are deleted or lost by accident during macOS reinstallation, you should have a backup of your data or getting files off first.

How to get files off when Mac is not turning on?

Step 6: Either after erasing the startup disk or getting files off the Mac, you can then go back to macOS Utilities and choose Reinstall macOS.

Reinstall macOS

Step 7: Follow the on-screen instructions and choose a disk to reinstall the OS.

  • If the internal startup disk is not showing up, or the installer says that it can't install macOS on your computer or volume, you might need to back up files and then erase your disk.
  • If the installer asks you to choose Macintosh HD or Macintosh HD - Data when installing macOS Catalina, choose Macintosh HD.

Other ways to install macOS

Apart from reinstalling macOS from macOS Recovery mode, you have other options according to your situations.

  1. Get released macOS versions or updates by App Store or Software Update preferences.
  2. Get macOS beta (such as macOS Big Sur) through Apple’s developer website.
  3. Create an external bootable installer disk to install macOS

Whatever your situation of reinstalling macOS is, you should always retrieve your data from the Mac before any further movement. After all, you can't tell if you want it back or not in the future.