Last edited: January 18, 2020
While you don't need a fresh install of macOS to use OpenCore, some users prefer having a fresh slate with their boot manager upgrades.
Note for legacy users
If you want to use OpenCore on a system without UEFI, please follow the Legacy Install section first, after you can continue following the Base folder structure section
To start we'll want to grab ourselves a copy of macOS, you can skip this and head to formatting the USB if you're just making a bootable OpenCore stick and not an installer. For everyone else, here's your options for obtaining macOS directly from Apple's servers:
Download the full macOS installer
BuildmacOSInstallApp then drag and drop the
macOS Downloads folder found in GibMacOS
Next we'll want to format our USB HFS+/MacOS Journaled with GUID partition map, must be 12GB for macOS Catalina.as-is recommended to name it
MyVolume as the script below can be used as-is.
Next run the
createinstallmedia command provided by Apple, note that the command is made for USB's formatted with the name
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)
Setting up OpenCore's EFI environment is simple, all you need to do is mount our EFI system partition. This is automatically made when we format with GUID but is hidden from the end user, this is where our friend mountEFI comes in:
You'll notice that once we open the EFI partition, it's empty. This is where the fun begins.