# Download and build macOS Installers

This doc is centered around downloading and writing the macOS installer to a USB. If you're already familiar with how to do this, you can skip.

  • Note: 16GB+ USB will be required for the installer

# Downloading

The simplest way to download macOS installs would be to use installinstallmacos:

[ ! -d ~/macOS-installer/ ] && mkdir ~/macOS-installer; cd ~/macOS-installer; [ ! -f ~/macOS-installer/installinstallmacos.py ] && curl -O https://raw.githubusercontent.com/munki/macadmin-scripts/main/installinstallmacos.py ; sudo python installinstallmacos.py
  • Note: On El Capitan (10.11) and older, you'll need to specify a catalog at the end of the command:
--catalogurl https://swscan.apple.com/content/catalogs/others/index-11-10.15-10.14-10.13-10.12-10.11-10.10-10.9-mountainlion-lion-snowleopard-leopard.merged-1.sucatalog

As you can see, we get a nice list of macOS installers. If you need a particular versions of macOS, you can select it by typing the number next to it. For this example we'll choose 10:

This is going to take a while as we're downloading the entire 12GB+ macOS installer.

Once finished, you'll find in your ~/macOS-Installer/ folder a DMG containing the macOS Installer, called Install_macOS_11.1-20C69.dmg for example. Mount it and you'll find the installer application.

  • Note: We recommend to move the Install macOS.app into the /Applications folder, as we'll be executing commands from there.
  • Note 2: Running Cmd+Shift+G in Finder will allow you to easily jump to ~/macOS-installer

# Building

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(Using GUID is important for the patcher). This will create two partitions: the main MyVolume and a second called EFI which is used as a boot partition where your Mac's firmware will check for boot files. EFI partitions will be hidden by default, so don't worry if you don't immediately see them.

  • Note: By default, Disk Utility only shows partitions – press Cmd/Win+2 to show all devices (alternatively you can press the View button)

Formatting the USB

Next run the createinstallmedia command provided by Apple (opens new window). Note that the command is made for USB's formatted with the name MyVolume:

sudo /Applications/Install\ macOS\ Big\ Sur.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume
  • Note: You can also replace the createinstallmedia path with that of where your installer's located (same idea with the drive name).

# Once finished, head to Building and installing OpenCore