macos-virt

The main goal of this project is to easily create macOS virtual machines that can be booted everywhere for things like development, testing or CI. The idea is not to provide a desktop like experience, more server-like. As such, GUI is working, but not the main goal.

macOS has very specific tastes in the hardware it supports. There has been extensive work by the hackintosh community to ease this to a maximum, but the real breakthrough came when using QEMU/KVM, since hardware could be emulated by the virtualization layer (except for the GPU).

This made running macOS dramatically simpler. And this is the approach this project is taking using Linux/QEMU/KVM has a Type-2 hypervisor for macOS, thanks to nested virtualization.

Most of the toolchain is sandboxed by Bazel and is expected to run on macOS.

Requirements:

macOS
bazelisk: brew install bazelbuild/tap/bazelisk
Docker for Mac (used by linuxkit)

Architecture

The architecture has several layers:

macOS
OpenCore bootloader
Linux/QEMU/KVM
Host OS

macOS

Most of the downloads and temporary files will reside in the work directory.

Installer image

First, create the installer image:

$ bazel run //macos:mkinstaller

Then choose which version of macOS you want to download and it will create the installer.

You'll end up with something like work/Install_macOS_10.15.5-19F2200.sparseimage.

macOS booted image

It is possible to install this image directly to an raw disk image without booting into the installer:

$ bazel run //macos:mkimage -- work/Install_macOS_10.15.5-19F2200.sparseimage macOS_10.15.5-19F2200.img

This will create macOS_10.15.5-19F2200.img, a raw bootable vanilla image.

It is vanilla and doesn't have anything hackintosh specific. It needs a bootloader.

OpenCore

The lower level bootloader for the image is OpenCore. It is an advanced bootloader that can do things like patching the kernel, passing custom arguments to the kernel, even out CPU specificities and so on.

The image is kept separate from the macOS one in order to iterate faster without rebuilding a complete macOS image.

To create the OpenCore boot image:

$ bazel build //opencore:image

The resulting image is bootable both in BIOS and UEFI mode (although UEFI is recommended).

Linux

In order to create a minimally bootable Linux image, linuxkit is used.

To create the linuxkit image, make sure Docker for Mac is running and then:

$ bazel build //linuxkit:image

This can take 90s+ so don't be worried.

This image expects the macOS image to be a block device attached to the virtual machine on /dev/sdb and will try to boot from it.

booter

The boot sequence is coordinated by //linuxkit/boot:boot. It will:

load the nescessary kernel modules (kvm, kvm-intel or kvm-amd)
setup NAT for the VM (tap interface and packet forwarding)
build the QEMU command line dynamically based on available CPU cores, memory and so on

steeve/macos-virt