Technology giant Apple Inc. is now moving towards Open Source as it released its flagship Operating system kernel (source code) on GitHub and ARM version of the kernel on Apple website. It is well known that most of the Apple products are closed source till now. So, it is considered as big move from the Tech giant.
XNU, acronym as XNU is Not Unix, is hybrid kernel combining the Mach kernel developed at Carnegie Mellon University with components from FreeBSD and C++ API for writing drivers called IOKit. XNU is used in MacOs and iOS operating systems. It is also used as the kernel for the iOS, tvOS, and watchOS operating systems.
MacOs (previously Mac OS X and later OS X), when initially released 2001, was build on the top of the NeXTSTEP, an operating system developed by NeXT. NeXT was the company build by Steve jobs, later merged with Apple.
NeXTSTEP itself is derived from open-source project BSD. That’s why the Mac you might be currently using relies heavily on open-source technologies. And that’s also why Apple releases a tiny, tiny portion of macOS every year. You can’t compile it and run your own version of macOS, but other kernel developers probably care about the source code of this kernel.
The kernel code released on GitHub, is having only one branch i.e., master branch with 101 commits as of now. In the documentation Apple covers all the necessary steps like ‘How to build XNU’, ‘Debug Information’, ‘Coding style’, ‘Testing the kernel’ etc. that might helpful for developer community.