How to install macOS on an external hard drive
How to install macOS on an external hard drive

Not too sure if macOS latest version will convince you? Are you testing the macOS beta version and wouldn’t take any chances? Then you will have to install macOS on an external drive. We explain how.

Installing the MacOs on an external drive is the best and safest way to view and test the latest Version operating system without having to change anything on your Mac. Installing external drive will leave your Mac current configuration intact and allow you to try a beta version or play around with Catalina.

If you’re testing the macOS Catalina beta version and don’t want to risk messing up your Mac system or are simply worried about updating your Mac to a new version of macOS, you don’t have to install the new update/beta version on your Mac your internal drive will be of good help to you.

In this tutorial, we will be explaining how to Install and run macOS from an external drive without errors.

Things you need

The USB-C or Thunderbolt 3 drive is a drive you need as it worth investing in as it will offer you a good connection.

Any external drive will finally have is used should have at least 12GB of space, but having more is recommended, in fact, when we ran Mojave beta on a 32GB flash drive we realized that it was not enough once we launched iCloud Desktop.

We will suggest getting the largest USB C/Thunderbolt 3 drive space you can afford if you want to run the beta Version or new Os if you were running it on your Mac.

Step 1: Installation

Follow these below instructions to get your hard drive or pen drive set for installation:

  1. Connect the Pen/external hard drive to your Mac.
  2. Launch the ‘Disk Utility’ (then press ‘Cmd + space bar’ and now type ‘Disk Utility’).
  3. Before this next step – if you are running High Sierra or later, you should click on the ‘View’ drop-down menu below the ‘Close’, then ‘Minimize’ buttons. Select ‘Show all devices’ from the options you get. You will now see the external root drive in addition to the volume below it.
  4. Select the unit in the sidebar.
  5. Click the ‘Delete’ icon.
  6. Choose the ‘Mac OS Extended’ (Journaled) as the format.
  7. Select the ‘GUID Partition Map’ as the scheme.
  8. Give your pen drive a name like “USB” or macOS Catalina”.
  9. Click the ‘Delete’ Icon.
  10. Wait while the disk utility creates the partition and configures the pen/external drive for you do note that it will take some minutes.
  11. Then click ‘Done’.


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Step 2: MacOS installation files

This process will depend on whether you want to run the full version of macOS or beta version or even an older Mac OS X.

To download the beta version of Catalina, for example, you will have to do the following:

  1. Sign up as a developer for the Public Beta program.
  2. Once you have completed the previous step, you can download the Public Access Utility Beta (or Access Utility Beta for Developers) from the Apple website.
  3. The beta access utility DMG file will eventually appear in your downloads folder. Once it arrives, open it up and click on ‘macOSPublicBetaAccessUtility.pkg’ to install it (it’s 215k).
  4. You may need to enroll your Mac. To check if your Mac is enrolled, open ‘System Preferences> Software Updates’ (in older versions of MacOS, App Store). If your Mac is enrolled, you will see “Your computer is configured to receive beta software updates ” appears.


  1. Once the Beta Access Utility is installed, the ‘Software Update’ tool will open and begin downloading the beta version. (If you are on an older version of macOS, you will be redirected to a Catalina page in the Mac App Store – you will not see it if you are not registered and running the login utility). Click ‘Download’ and wait while it downloads to your Mac. The download may take a while, as the file is larger than 5GB, but you should be able to continue working while the download is in progress.

  1. Once the download is complete, your Mac will launch it. WARNING: You are not planning to install it on your Mac, so DO NOT CLICK CONTINUE. Instead, exit the installer.
  1. You will find the ‘Install macOS Catalina Beta’ installer in your Applications folder.

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Step 3: Install macOS on the external drive

Now, to install the beta or alternative version of the Mac operating system on your external hard drive:

  1. Open a search window, go to ‘Applications’ and find the Catalina Beta installer (or whatever version of macOS you are running).
  2. Click on the installer.
  3. In the first window, to configure the installation of macOS Catalina Beta (or whatever) click on ‘Continue’.
  4. Accept the software license agreement.
  5. Next, and this is important, click on ‘Show all disks’. Please don’t click ‘Start’ as you don’t want to install on the main unit.
  6. Click on the external drive.
  7. Click on ‘Install’.

Wait while the macOS version installs on the drive. This process can take a long time, so don’t despair.

These steps will not have worked if you did not configure the external drive as a GUID partition.

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Step 4: Run macOS on the external drive

There are two ways to run the macOS version from your external drive.


  1. Open ‘System Preferences> Startup Disk’.
  2. Select the external drive you want to use to start your Mac and click ‘Restart’.


  1. Hold down the ‘Option / Alt’ keys during startup.
  2. Choose the drive you want to use to start up your Mac.


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