Linux is not in the public domain. Linux is a cancer that attaches itself in an intellectual property sense to everything it touches. That's the way that the license works.
Bio: Paracelsus, born Philippus Aureolus Theophrastus Bombastus von Hohenheim, was a Swiss German philosopher, physician, botanist, astrologer, and general occultist. He is credited as the founder of toxicology.