Thursday, February 6, 2020

How to Run an Old Version of macOS After Upgrading to Catalina

I have a MacBook Pro, which I'm usually happy with.

However, I recently wanted to play a game that's only available on Windows. So, I went about figuring out how to run Windows software on a Mac.

After some initial investigation, I had the following options:
  1. Run Windows in a virtual machine using software like VirtualBox or Parallels
  2. Install and run Windows on my laptop using Apple's Boot Camp
  3. Use a virtual Windows desktop using a product like Amazon WorkSpaces
  4. Use a compatibility layer to run the Windows application on my laptop without a Windows install using Wine or Crossover
I decided to dig deeper into using Wine because I didn't want to buy a Windows license or make recurring payments to Amazon.

Unfortunately, macOS Catalina (which is what I have) doesn't support 32-bit applications and the game I wanted to play requires 32-bit support. So, to run the game using Wine, I'd need to use an older version of macOS.

I wasn't willing to downgrade my OS for this, so I started looking into how to run multiple version of macOS on my laptop. Here's what I found:


To run a different version of macOS on the same laptop, we'll:
  1. Create a disk partition to hold a "bootable installer"
  2. Create a bootable installer for the older macOS version on that partition
  3. Create a disk volume to install the OS on
  4. Install the OS on that volume
WARNING: Creating, modifying, and erasing partitions can have serious consequences. You're at your own risk if you decide to attempt this.

Step 1: Create a disk partition

To create a bootable installer, we need somewhere to put it. A good option is a thumb drive. I didn't have one on hand, so I created a disk partition on my mac.

Basically, I followed Apple's instructions the instructions for creating a physical disk partition. The following are important:
  1. About 8GB of capacity is needed
  2. The partition must be formatted as "Mac OS Extended"
Here's how I set up my partition:
  1. Open Disk Utility and select "Show All Devices".
  2. Select the physical hard drive in the left panel and click the "Partition" button on the top.
  3. Select an existing partition in the pie chart, from which the new partition will be created (the existing partition will "donate" disk space for the new partition). Then, click the "+" button.
  4. Give your partition a name (the name is arbitrary - just use something you'll remember), select "Mac OS Extended (Journaled)" as the format, and set the size to 10 GB.
  5. Click "Apply" and be patient while the new partition is created.

Step 2: Create a bootable installer

For this step, I followed Apple's instructions for creating a bootable installer.

For me, this involved:
  1. Download macOS Mojave.
  2. Quit the installer (it started automatically after download, but we need to run it from the command line).
  3. Open a Terminal window.
  4. Run createinstallmedia on the new disk partition created in step 1:
    sudo /Applications/Install\ macOS\ --volume /Volumes/Bootable\ Install\ Partition.
    Note that your paths might differ. The second one depends on what you named your partition.
  5. Follow the prompts. Note that after this completes, the partition is renamed to something like "Install macOS Mojave".

Step 3: Create a new volume

We need to create a new volume on which to install the OS.
  1. Open Disk Utility again.
  2. Select the volume where macOS Catalina is installed. For me, this is "Macintosh HD".
  3. Click the "+" above "Volume" at the top.
  4. Enter a name for the new volume (I used "Mac OS Mojave"), leave the format as APFS, and click "Add".
  5. Wait while your new volume is created.

Step 4: Install the OS

Now, we just use the bootable installer from step 2 to install the OS on the new volume from step 3.
  1. Restart the laptop while holding down the option key. For additional guidance, see the "Use Startup Manager" section of Apple's guide for selecting a different startup disk.
  2. Once the laptop restarts, select disk with the bootable installer. For me, it was the one named "Install macOS Mojave".
  3. Begin installation by selecting Install macOS.
  4. Go through the install process. When prompted to select a partition to install the OS on, select the one created in step 3.


That's it! After installation, your computer should startup in the OS you installed.

If you want to get back to your main OS installation, just follow the same procedure for using the startup manager (restart while holding the option key) and select it (for me, it's called "Macintosh HD").

So, after all this, I was able to run my Windows game on my Mac laptop by booting into the macOS Mojave install and using Wine.

All this so I could play a stupid game.. 😂🤦

I hope this helps with whatever you need it for!