macoOS Mojave

If something doesn't quite work right after you've installed macOS Catalina, you can reinstall the operating system so it is a fresh copy. Reinstalling a fresh copy of macOS Catalina will not affect your current settings. Applications and settings will remain the same. Completing this process replaces the core files of macOS Catalina in case something wasn't working right before.

Before you start: Back up your data

  • It is a good idea to perform one full backup before starting with a clean copy of macOS Catalina. You can also back up files and documents using a cloud-based storage system like Dropbox, OneDrive, or the easiest: iCloud.

  • Make sure the computer on which you're installing a fresh copy of macOS Catalina can be connected to the internet, either via Wi-Fi or Ethernet. This step is important. An Internet connection is needed in order to reinstall the macOS operating system.

  • If you are using a laptop, make sure it is connected to a power source.

How to install a new copy of macOS Catalina in Recovery Mode

Recovery Mode is the special salvation of the Mac that first launched with OS X 10.7 Lion. It creates a temporary boot partition that allows you to access certain things on your computer that you might not be able to if your system froze or crashed. It is the easiest way to install a fresh copy of an operating system.

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  1. Connect your Mac to the internet via Wi-Fi or Ethernet
  2. Click on the Apple icon in the upper left corner of your screen.
  3. Select Restart from the drop-down menu.

    Restart your Mac

  4. Hold down Command and R (⌘ + R) at the same time. When you hear the startup chime (or when the screen goes black on newer Macs), keep holding the keys until your computer reboots.
  5. Click on Reinstall a new copy of macOS.
  6. Click Continue.

    Reinstall macOS Sierra

  7. Click Continue again when the installer window appears.
  8. Agree to the software terms and conditions.
  9. Select your hard drive.
  10. Click Install.
  11. Complete the installation process.

    Reinstall macOS Sierra

How to update to Catalina after reinstalling an earlier macOS

When you install the latest operating system from Recovery Mode, sometimes, your Mac will install an older operating system, like High Sierra or Mojave. Once the older operating system installation is complete, you can then download Catalina as a software update.

Remember, you must have an internet connection in order to download a fresh copy of the Mac operating system.

  1. Open System Preferences.
  2. Click on Software Updates.


  3. Click on Update Now.

Any questions?

Do you need help reinstalling macOS Mojave on your Mac? Post your questions in the comments and I'll do my best to help troubleshoot your issue.

Updated September 2019: Updated for the public launch of macOS Catalina.

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