How to perform clean install of macOS Catalina (Instruction)

Easy way to Clean Install mac OS Catalina

macOS Catalina is Apple’s shiny operating system for the Mac that has been around for a while, and it’s got a ton of great features and improvements. You’re probably keen to get started and install it straight away. Before you do, consider whether you want to install it over the top of your current OS or as a completely clean install of macOS Catalina. The benefits of the latter are that it will be like a completely new Mac, with all your settings wiped out and junk files gone. It should make your Mac run faster. The rest of this article will explain how to clean install macOS Catalina.

Tip: Clear out the junk before installation.

Before the clean installation of macOS 10.15 Catalina, it’s recommended that you first delete junk and dusty files from the current macOS. There are many free and paid tools to clean junk, but the quickest option is to run CleanMyMac X. You can expect to free up tens of gigabytes of space, including old apps and their leftovers.

Here’s how it works:

  1. Download and install CleanMyMac  — try a free edition of the app here.
  2. Choose the System Junk tool.
  3. Press Scan.
  4. When it’s finished, either press Remove to get rid of all the files it recommends or choose Review to look through what it’s found and decide for yourself what to delete and what to keep.

Backup your Mac

I can’t stress how important this is. You must back up your Mac before you do anything else. You’re going to be erasing your startup drive completely, so you need a complete backup of everything. You can use Time Machine, another backup app, or a cloning tool. Just make sure you have a complete, preferably bootable, copy of your current installation. 

You should also make notes of settings for apps you regularly use — screen grabbing them is a good way to do that. And you should make sure you have a copy of any license codes that you’ll need when you reinstall applications. You can use Apple’s Notes app to make notes, as long as you sync them with iCloud.

Create a bootable installer of macOS Catalina

If you’re reading this, you can download macOS Catalina from the Mac App Store, as it has shipped already, and then choose Quit when the installation starts.

If you’re clean installing the beta (and, by the way, that’s not something I would recommend), it’s much better to create a dual boot system when you run the beta.

  1. Grab a USB stick with a capacity of at least 16GB or an external hard drive.
  2. Go to Applications > Utilities and launch Disk Utility. 
  3. Launch Disk Utilities and Erase the Drive or USB stick, formatting it as Mac OS Extended (Journaled) or APFS and selecting GUID partition map if a selection is available.
  4. The easiest method for creating a  bootable installer is to use DiskMaker X. However, if you’re comfortable using Terminal, you can do it like this:
    1.  Launch Terminal from Applications>Utilities.
    2.  Type: sudo /Applications/Install\ macOS\ Catalina\ --volume /Volumes/Untitled --applicationpath /Applications/Install\ macOS\ Catalina\ where ‘Untitled’ is the name of your USB stick or external hard drive.
    3.  Press Return and wait for the word Done to appear in Terminal.

Once you see ‘Done’ in Terminal, you can quit it. Your USB stick or external hard drive is now a bootable Catalina installer, so keep it safe. Now, it’s time to clean install macOS Catalina.

Did you know?

macOS Catalina is not compatible with Apple silicon. However, it is still a great fit for older Mac models that cannot run newer macOS versions.

How to clean install macOS Catalina

Now that you’ve made a backup and created a bootable installer, it’s time to actually install the new macOS. Follow these easy steps to clean install macOS Catalina on your Mac:

  1. Plug your USB stick or external hard drive into your Mac if it’s not plugged in already.  
  2. Restart your Mac while holding down the Option key.
  3. When you see the options for booting appear on screen, choose the installer disk you just created.
  4. When you see the macOS Utilities screen appear, choose Disk Utility.
  5. When Disk Utility launches, choose the Eras tab, then select your startup volume (probably called Macintosh HD).
  6. Give your startup disk a name, then choose a format. If you have a recent Mac with an SSD startup disk, select APFS. If you have an older Mac with a mechanical hard drive or Fusion Drive, choose whichever one you want to use.
  7. Choose Erase.
  8. When Disk Utility has finished erasing the disk, quit it to return to the macOS Utilities screen.
  9. Choose Install macOS.
  10. Press Continue and choose the drive you just erased and re-formatted as the destination.
  11. macOS Catalina will start to install.
  12. When it’s finished, your Mac will restart, and it will look like a brand-new Mac. Go through the set-up process to set up a user account, add your wifi network, choose a language, and log in to iCloud.

Once you’ve set up your Mac, you can eject the installer disk and remove it. Remember to keep it safe. You can now restore files you backed up earlier from Time Machine or whichever backup tool you used. Remember to restore files and folders individually. Don’t, for example, restore your entire user directory; otherwise, you’ll copy back all the junk files you just got rid of. Reinstall applications and go through them, adding license details where necessary. Check that everything works as you expect it to, and use the screenshots you made earlier to configure settings.

There are lots of good reasons why you might want to clean install macOS Catalina, but the most important one is that it should make your Mac feel like new and keep it running smoothly. For ultimate Mac refresh, you can also download CleanMyMac X and play with its cleanup tools. Getting rid of old junk feels great.

Laptop with CleanMyMac
CleanMyMac X

Your Mac. As good as new.