Unix is distinguished by a simple, coherent, and elegant design — truly remarkable features that have enabled the system to influence the world for more than a quarter of a century. And especially thanks to the growing presence of Linux, the idea is still picking up momentum, with no end of the growth in sight. Unix and Linux carry a certain fascination, and the two quotations above hopefully capture the spirit of this attraction. Consider Dennis Ritchie’s quote: Is the coinventor of Unix at Bell Labs completely right in saying that only a genius can appreciate the simplicity of Unix? Luckily not, because he puts himself into perspective immediately by adding that programmers also qualify to value the essence of Unix. Understanding the meagerly documented, demanding, and complex sources of Unix as well as of Linux is not always an easy task. But once one has started to experience the rich insights that can be gained from the kernel sources, it is hard to escape the fascination of Linux. It seems fair to warn you that it’s easy to get addicted to the joy of the operating system kernel once starting to dive into it. This was already noted by Benny Goodheart and James Cox, whose preface to their book The Magic Garden Explained (second quotation above) explained the internals of Unix System V. And Linux is definitely also capable of helping you to lose your mind!