First, you need a 16GB or above USB because Mojave is over 6GB and Catalina is over 8GB. we’re gonna need to partition your USB into 2(for both OS).
- Plugin your USB drive
- Go to
above, you will see your external drive, in my case partition button was greyed out, if this is also your case, you need to run some commands in the terminal:
Enable partition — skip if partition enabled
diskutil erasedisk hfs+ External GPT /dev/disk4 . /dev/disk4 being your usb drive path.
Once that’s done you’re gonna be able to click the partition button, and do the partition:
Setting up partition
1. Select your drive and click Partition above(Still in Disk Utility)
2. Click the
3. If the plus button is disabled, select the Mac OS Extended (Case-sensitive, Journaled) option in
4. In this partition you need to make sure that each has enough space for both OS, move the grey dots to adjust the space for each device.
5. Hit apply and you should have two drives(1 with 6GB and 1 with 8GB)
Now that we’re done partitioning our USB, let us proceed to set it as bootable.
Create a bootable installer
Mojave and Catalina— after downloading both, you should have
Install macOs Catalinaand
Install macOs Mojaveinside your
2. Next, open your terminal and run this command:
sudo /Applications/Install\ macOS\ Catalina.app/Contents/Resources/createinstallmedia --volume /Volumes/Catalina
the command above will put your Catalina installer to your selected drive, replace
/Catalina at the end of this command with the name of your drive. (The 8GB drive in our partition earlier.)
3. Press Return after typing the command.
4. When prompted, type your administrator password and press Return again. Terminal doesn’t show any characters as you type your password.
5. When prompted, type
Y to confirm that you want to erase the volume, then press Return. Terminal shows the progress as the bootable installer is created.
6. When Terminal says that it’s done, the drive will have the same name as the installer you downloaded, such as Install macOS Catalina. You can now quit Terminal and eject the drive.
You should see the image above once it’s done and your installer for Catalina is ready!! Now you just have to repeat the same process to setup Mojave installer, but use this code instead, in step no 2:
sudo /Applications/Install\ macOS\ Mojave.app/Contents/Resources/createinstallmedia --volume /Volumes/<your other drive name>
Now you have a multi-boot USB macOS installer!! just like the image below. Enjoy installing! 😊
To see my sources and more info, check out the full story on my website here: Multi-bootable USB Installer For Catalina and Mojave macOS