How to Install MacOS Catalina Beta on APFS Volume to Dual Boot with Mojave

Jul 25, 2019 - 6 Comments

How to dual boot MacOS Catalina and Mojave

If you want to run MacOS Catalina Beta alongside macOS Mojave or macOS High Sierra, you can do so by adding a new APFS volume to the Mac if that Macs hard drive is formatted as APFS. This effectively creates a dual boot scenario for MacOS Catalina 10.15 and Mojave 10.14.x (or High Sierra), and offers an alternative approach to simply installing MacOS Catalina Beta on a Mac as the primary operating system. There are a few advantages to this approach, notably that you can use a single Mac for running the two operating systems, and you won’t need to designate storage capacity for Catalina as it will share the drive space with the other MacOS release and expand as needed.


Important: This is for advanced Mac users only. There are mixed reports of problems with running MacOS Catalina alongside other macOS releases, particularly for Macs with T2 security chips and Touch ID. Be absolutely certain you have a full backup of your data and Mac before attempting this.

To get started, you’ll need a full backup of the Mac and all data on the computer, a Mac compatible with MacOS Catalina, you’ll need to be enrolled in the MacOS Catalina beta testing program, and you’ll need a minimum of 35GB of free disk space available though more is recommended for best results with trying Catalina.

How to Install MacOS Catalina in an APFS Volume Alongside MacOS Mojave / High Sierra

This will create a dual boot environment allowing you to switch between MacOS Catalina and MacOS Mojave or High Sierra.

  1. Back up the Mac with Time Machine or your backup method of choice, do not skip this step
  2. Open Disk Utility on the Mac and create a new APFS volume by clicking on the “+” plus button
  3. Name the new APFS volume something obvious like “Catalina” and click “Add” (optionally you can adjust size options but this is not necessary)
  4. Add a new APFS volume for MacOS Catalina

  5. Click “Done” and then quit Disk Utility when finished
  6. Open the “Install MacOS Catalina Beta” application found in the /Applications folder (you can also use a MacOS Catalina USB boot drive if you made one) and click “Continue” then read and agree to the terms of service
  7. Click on “Show All Disks”
  8. Choose Show All Disks to find the other disk volume to install Catalina onto

  9. At the disk selection screen, choose the alternate “Catalina” APFS Volume you created earlier as the target disk, then click on “Install” to install MacOS Catalina Beta onto that volume
  10. Choose the proper APFS volume to install MacOS Catalina onto

  11. Let the entire MacOS Catalina installation complete, the Mac will reboot and the process will take a while to finish

When the installation completes and the Mac reboots for the final time, the computer will start directly into MacOS Catalina.

How to Switch Booting of MacOS Catalina or MacOS Mojave / High Sierra

You can switch between booting and running MacOS Catalina and MacOS Mojave or High Sierra by doing either of the following:

Switching Boot macOS Versions on System Start

  • Restart or boot the Mac and immediately hold down the OPTION key, then at the boot selection screen choose the macOS volume you wish to boot from

Switching Boot macOS Version via System Preferences

  • Pull down the  Apple menu and go to “System Preferences” and then go to “Startup Disk” and choose the volume / OS to boot from

Removing MacOS Catalina APFS Volume

If you wish to remove MacOS Catalina Beta, you can simply open Disk Utility and delete the APFS volume that you created to install MacOS Catalina onto.

How to remove the MacOS Catalina APFS volume

Since you are not upgrading or installing MacOS Catalina over an existing MacOS release or as the only operating system on the computer, the typical downgrade Catalina method is not necessary (unless you wanted to format and erase the entire Mac and all volumes, anyway).

Have you installed and run MacOS Catalina in an APFS volume? Did you use another method? Do you have any particular tips, advice, reports, or experiences you wish to share? Share with us in the comments below!

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Posted by: Paul Horowitz in Mac OS X, Tips & Tricks

6 Comments

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  1. Erich says:

    I already installed Catalina, now i found, Idee Mojave as well. Where can I get Mojave get create a second APFS Startup volume or an USB boot drive?

  2. Uli says:

    Hi Paul,

    Question: Right now I have Mojave on my iMac, but I want to update to Catalina as it came out today.

    Though I still need a dual boot option with Catalina and Mojave as I have some older audio-editing apps with 32bit that I need sometimes.

    So I would first update my Mojave to Catalina.

    Then create an APFS Volume (Step 1-4)

    Then instead of step 5 go to https://apps.apple.com/de/app/macos-mojave/id1398502828?mt=12 and get Mojave, in beginning of installation process it will go to Step 6, right?

    So at Step 6 Click on “Show All Disks” I choose the newly created volume and install Mojave there

    Let the install process finish and boot holding “option” and choose which of both OSX I want to boot with

    So later when I don’t need Mojave no more for my 32bit audio apps I would just delete the Mojave volume.

    Would that work?

    (Off course I make a TimeMachine backup first! ;)

    Tks, Uli

  3. Brian says:

    Hi Paul,
    Any advice on how to replace the Catalina Recovery partition with a Mojave version?

    • Paul says:

      The most consistently reliable way is to format the drive and reinstall MacOS Mojave again, not ideal obviously but it does work to rebuild the Mojave recovery partition.

      You could also attempt to erase the Catalina recovery partition manually and then rebuild a new one manually using a script or third party tool, but it may not work for Mojave (mixed reports in the comments on the following article, and things may be different with Catalina anyway).

      http://osxdaily.com/2016/07/03/recreate-recovery-partition-mac/#comment-6255971

      Ultimately it’s likely best to just reinstall MacOS Mojave.

  4. Brian says:

    Just a heads up for anyone wanting to test the 10.15 beta, you’ll no longer have the ability to boot into recovery to reinstall Mojave. You’ll only be given the option of reinstalling the Catalina Beta. If you need to reinstall Mojave you’ll need to do a clean install with the latest 10.14.x version that is available from the App Store. This will overwrite your current install necessitating a Time Machine or cloned backup to recover your data. I found that booting using Command+R was not effective and now need to use Command+Option+R to access Recovery. For anyone thinking that installing the 10.15 on an external SSD will sidestep this issue, it won’t, you’ll experience the same problem. This problem has never arisen before when testing out a new Apple OS.

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