How to Make a Bootable macOS Catalina 10.15 Beta USB Installer Drive
This process requires using the command line, if you are not comfortable using the Terminal than it is better to avoid this process. Mistakes with syntax can lead to permanent data loss, or the erasure and formatting of the wrong disk, so proceed at your own risk.
What you need to create a bootable installer
A USB flash drive or other secondary volume formatted as Mac OS Extended, with at least 14GB of available storage
A downloaded installer for macOS Monterey, Big Sur, Catalina, Mojave, High Sierra, or El Capitan
Connect the USB flash drive to the Mac if you haven’t done so already, name the drive “UNTITLED”
Open the “Terminal” application, it’s found in the Utilities folder and you can also launch it from hitting Command+Spacebar typing Terminal and hitting return
Enter the following command at the Terminal command line, assuming “UNTITLED” is the name of the USB flash drive you want to make into the Mac Catalina installer boot disk:
sudo /Applications/Install\ macOS\ Catalina.app/Contents/Resources/createinstallmedia --volume /Volumes/UNTITLED
If the syntax is correct, hit the Enter/Return key and authenticate with the admin password as necessitated by sudo
Let the creation process build the boot installer disk and complete, it may take a little while
After the MacOS Catalina 10.15 USB boot installer drive has been created, it will be mounted on the Mac. At this point it can be used like any other boot disk or installation disk.
The MacOS Catalina boot disk can be used with any MacOS Catalina compatible Mac.
* If you see a “command not found” error message in the terminal, it’s likely because there was a typo or syntax error, or because the “Install macOS Catalina.app” application file was not found in the /Applications/ folder where it is expected to be.