Why hasn't the XNU kernel been extensively used despite the open source licence offered by Apple?

Is it because of specific licensing issues? Or because Linux is technologically much better for reuse ? Or is it a market with one winner, Linux?

2 Answers 2


On one hand, Linux had a considerable head start on XNU, having been first released in 1991. While I can't seem to find information on a release date for XNU, I'm quite sure it happened after Apple acquired NeXT, in 1997.

Also, the kernel design used in XNU may not be easy for some developers to get their head around. Linux is a monolithic kernel, while XNU is a hybrid (a cross between monolithic and micro kernel models) It's possible that developers are more comfortable developing for the former model than the latter. Ken Thompson, one of the fathers of UNIX, also argued this point.

More information can be found on Wikipedia (starting at Kernel)

  • XNU has been aroundsince NexTStep in the late 80s - the Open source base Mach since mid 80s
    – mmmmmm
    Apr 26, 2013 at 8:24
  • According to wikipedia, XNU has been developed by apple since 1996(its initial release).
    – tsturzl
    Jul 10, 2016 at 18:46

As noted by OpenStep developers:

Apple has been making available certain drivers in binary form under the Apple Binary License. Without these, Darwin in its current form would not be usable (in fact, not even the XNU kernel could boot).

  • 2
    A fuller version of the quotation can be found here.
    – GDP2
    Aug 20, 2017 at 2:58

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