Please note: This page has not been updated to take changes made in Darwin 10, or later into account.

This page is about the XNU kernel.

Both Apple vanilla mach_kernel and Voodoo xnu-dev are available and functional in PureDarwin.

It is a work in progress. Please contribute.

XNU is the kernel used by Darwin and Mac OS X (similar to what GNU/Linux kernel is in a Linux distro). XNU acronym stands for "X is Not Unix" (although Mac OS X has been Unix certified in 2007).

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• Not a microkernel (although using parts of the Mach microkernel)
• Not 64-bit (although able to run 64-bit binaries)
• Not so hard to recompile See here why the term kernel is used somewhat differently than you might expect.

• Mach 3.0
• BSD
• I/O Kit

XNU cannot boot by itself, since it always needs a certain set of kernel extensions (kexts) to be present. However, you can create a mach_kernel file that not only contains XNU itself, but also a defined set of kexts:

kextcache -a i386 -K  /Volumes/PureDarwin/mach_kernel  -c /tmp/mach_kernel.prelinked /Volumes/PureDarwin/System/Library/Extensions

The result is that you should have a file in /tmp/mach_kernel_prelinked that contains both XNU and the kexts.

Another example, fast boot and kext autoloaded:

kextcache -a i386 -s -l -n -c "$MOUNT/System/Library/Caches/com.apple.kernelcaches/kernelcache.DEADBEEF" -k -K "$MOUNT/mach_kernel" -m "$MOUNT/System/Library/Extensions.mkext" "$MOUNT/System/Library/Extensions"

• http://en.wikipedia.org/wiki/XNU 
• http://osxbook.com/book/bonus/ancient/whatismacosx/arch_xnu.html 
• http://code.google.com/p/xnu-dev/