How To

How to Clean Install macOS Catalina and Dual Boot with Mojave

Written by John

MacOS Catalina is the latest instalment in the macOS series of operating systems. With its introduction come plenty of innovative features which include but are not limited to. Watch your app usage through the amount of screen time it takes up. The ability to use your iPad if you have one as an external screen. Enhanced accessibility features such as Voice Control that allows you to have a 100% voice-controlled experience.

Speaking of Catalina, Apple has just released a Public Beta 1. Today we’re going to give you some instructions to follow should you want to dual boot macOS Catalina alongside Mojave. So why do I need a fresh and clean install of Mac OS to allow it to dual boot it alongside macOS Mojave:

  • Being as it’s currently in Beta mode; the OS itself is unstable and has unresolved issues.
  • Natively you’d already have to use a Mac for your day to day job, but you want to try out a new OS.
  • A final version of Catalina is not yet available, so this is your only choice.
  • Once macOS Catalina becomes stable, you can delete your Mojave partition.

How to Clean install macOS Catalina and Dual Boot with Mojave

Step 1: Downloading macOS 10.15 Catalina

Before proceeding with this step, it’s vital to ensure that firstly, you’ve backed all of your data up, and secondly, that you’re fully enrolled within the Beta Software Program. Once the two of them have been done, we’re going to want to download macOS public beta access utility by downloading it from the developer website.

To download macOS Catalina, you’ll need to sign in with your Apple ID and scroll down the list of available OS’s until you stumble across Catalina. The install has finished you’ll find the installation file within your ‘Applications Folder’.

Step 2: Now We need to Create a USB Installer for the new macOS Catalina 10.15

The first step in this process involves connecting your USB stick into your Mac. Once you’ve done this open up a Terminal by navigating to Applications, then to Utilities, then to Terminal.

You’re now going to want to rename your inserted USB flash drive as ‘USB’. Once you’ve done that the next step is to enter the following line of code in the command line of your terminal:

sudo /Applications/Install\ macOS\ Catalina\ Beta.app/Contents/Resources/createinstallmedia --volume /Volumes/USB –nointeractions –downloadassets

Once you’ve done that you’ll take note that the Terminal application now needs your password an admin to authenticate the command above. Sudo requires admin access. Finally, once you’ve done all the above the USB installer drive should have been created, and you should now be able to install macOS Catalina through your USB drive installer.

Create a macOS Catalina USB Installer

Step 3: Creating a New Partition ready for macOS Catalina

Mac OS Catalina will require its own partition on your hard drives for it to run, so let’s go ahead and create a partition ready for it to be installed in:

Create a New Partition for macOS Catalina

  • First, you’re going to want to open the Disk Utility program, if you don’t know where this is to navigate to your Applications folder or alternatively you can search for it.
  • Once Disk Utility has been opened click on your macOS Hard Drive which for the purposes of this example will be your existing Mojave OS.
  • Once you have selected Mojave, go ahead and click ‘Partition’ and then [+], it should now start creating a partition.
  • You’re going to want to name the partition macOS Catalina, allocate around 25GB-100GB for it and select the format of the partition as APFS.
  • Once you have done all of the above clicks apply and wait for the changes to save.

Step 4: Installing the macOS Catalina on Your Newly Formed Partition

Now that we’ve created our partition it is now time to install macOS Catalina on this newly formed partition and so to do this you’ll need to follow these steps:

  • First and foremost ensure there is a connection present between the USB Installer and your Mac.
  • Restart your Mac. Upon it rebooting straight away hold down your ‘Option’ key until a boot menu appears.
Boot to macOS Catalina USB Installer

  • Once you see this boot menu, go ahead and highlight Install macOS Catalina and press Enter.
  • The next window you’ll see is a macOS Utilities Screen, then select "Install macOS" on here it’ll ask you to select your desired drive you want to install on, select the “macOS Catalina” drive we partitioned before and then follow the tutorial through.
Clean Install macOS Catalina on new partition

Step 5: How to Dual Boot both macOS Mojave and macOS Catalina at the same time

Once you have successfully installed macOS 10.15 Catalina on the drive we partitioned before, whenever you switch your Mac on you’ll find that it will always by default now be booting to Catalina, however, if you want to use macOS Mojave still on occasions follow these steps:

Dual Boot with Mojave

  • Navigate to System Preferences which can also be found by going to the Apple logo in the top right.
  • Click on the lock icon and enter the password it is requesting off you.
  • When it asks you to select a partition to select the macOS Mojave as opposed to Catalina and allow the machine to restart. Then click "Restart" button.
  • Once your Mac has restarted, it will boot into Mojave, to switch back to Catalina follow these instructions again but select the Catalina Partition.

Bottom Line

Being able to install and use macOS Catalina early on, especially as a developer, allows you to be one step ahead of everyone else in terms of developing new programs or even just getting used to the new features. Hopefully, this guide here today has clearly explained to you how you can install Mac OS Catalina alongside macOS Mojave with ease allowing you to dual boot them both depending on which one you might want to us at any moment in time.

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