For machines that need a specific OS release or can’t download from the AppStore, you can use the GibMacOS utility.
Now lets grab GibMacOS, unzip on a local directory.
Next run the gibMacOS.command:
As you can see, we get a nice list of macOS installers. If you need beta versions of macOS, you can select C. Change Catalog. For this example we’ll choose 1:
This is going to take a while as we’re downloading the entire 8GB+ macOS installer, so highly recommend reading the rest of the guide while you wait.
Once finished, we’ll next want to run the BuildmacOSInstallApp.command:
You will be prompted for the macOS installer files which were downloaded to macOS Downloads folder in the GibMacOS directory.
From the Finder, drill down to the folder containing the downloaded files and either drag it to the command line or “Cmd+C” and paste it to the terminal.
Once the task is completed exit the utility, you will find the Install file in the directory.
Move the newly created image to Applications folder, this will simplify the next section.
#Setting up the installer
Now we’ll be formatting the USB to prep for both the macOS installer and OpenCore. We’ll want to use macOS Extended(HFS+) with a GUID partition map. What this will do is create 2 partitions. The main MyVolume and a second called EFI which is used as a boot partition where your firmware will check for boot files.
- Note by default Disk Utility only shows partitions, press Cmd/Win+2 to show all devices(Alternatively you can press the view button)
Next run the createinstallmedia command provided by Apple, note that the command is made for USB’s formatted with the name MyVolume:
sudo /Applications/Install\ macOS\ Catalina.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume
This will take some time so may want to grab a coffee or continue reading the guide(to be fair you really shouldn’t be following this guide step by step without reading the whole thing first)
You can also replace the createinstallmedia path with that of where your installer’s located, same idea with the drive name.