Lions’ Commentary on UNIX

Lions Commentary on UNIX


AUTHOR John Lions
PAGES 254 pages
TYPE Paperback
PUBLISHED August 1996
PRICE $44.95 US
$59.50 CAN
  • Named “Book of the Year” by Unix Review magazine in 1996 (though already 20 years old!)
  • Used as an operating system textbook at MIT (when it was already 30 years old!)
  • Brian Kernighan, co-author with Dennis Ritchie of the famous C Programming Language book (“K&R”), gave a May 2021 testimonial to the importance and enduring value of the Lions book

“After 20 years, this is still the best exposition of the workings of a ‘real’ operating system.”
— Ken Thompson, co-developer of UNIX, 1996

“After years of suppression (as trade secrets) by various owners of the UNIX code, this tome has been re-released, and we owe a debt to all involved in making this happen. I consider this to be the single most important book of 1996.”
— Unix Review, June 1997

“Lions’ commentary was a unique document in the world of computer science, containing a kind of key to learning about a central component of the computer, one that very few people would have had access to in the 1970s. It shows how UNIX was ported not only to machines (which were scarce) but also to the minds of young researchers and student programmers (which were plentiful). Several generations of both academic computer scientists and students who went on to work for computer or software corporations were trained on photocopies of UNIX source code, with a whiff of toner and illicit circulation: a distributed operating system in the textual sense.”
— Christopher M. Kelty, Two Bits: The Cultural Significance of Free Software, 2008

“Hackers, likewise, can learn to program by looking at good programs— not just at what they do, but at the source code…When I learned to program, we had to rely mostly on examples in books. The one big chunk of code available then was UNIX, but even this was not open source. Most of the people who read the source read it in illicit photocopies of John Lion’s book…”
— Paul Graham, Hackers & Painters, 2004

To Place an Order
American customers: Please contact your favorite bookstore to purchase paperback copies (a few stores with large computer book selections are listed below). Bookstores can backorder copies from Ingram, the nation’s largest book wholesaler, which will fulfill their order within a few days (tell the bookstore its a “Lightning Source” title).

Non-USA customers: International print-on-demand and wholesale distribution is available: Lightning Source UK for the United Kingdom, Lightning Source Global Connect for (as of July 2021) Brazil, China, Germany, India, Italy, Japan, Poland, Russia, South Korea, and Spain).

About Lions’ Commentary on UNIX 6th Edition, with Source Code

The Lions book“, cherished by UNIX hackers and widely circulated as a photocopied bootleg document since the late 1970’s, is finally available again in an unrestricted edition. This legendary underground classic, reproduced without modification, is really two works in one:

  • the complete source code to an early version (Edition 6) of the UNIX operating system, a treasure in itself!
  • a brilliant commentary on that code by John Lions

Lions’ marriage of source code with commentary was originally used as an operating systems textbook, and it remains uniquely well suited for that purpose. As a self-study UNIX conceptual tutorial, it has informed and inspired computer professionals and advanced operating system students for over twenty years. UNIX insiders have cherished, and zealously guarded, pirated photocopies of this manuscript, a “hacker trophy” of sorts.

Lions Book n. —- “Source Code and Commentary on UNIX Level 6”, by John Lions…for years the only detailed kernel documentation available to anyone outside Bell Labs. Because Western Electric wished to maintain trade secret status on the kernel, the Lions book was never formally published…In spite of this, it soon spread by samizdat to a good many of the early UNIX hackers.

New Hackers Dictionary 2/e, by Eric S. Raymond, MIT Press 1993

The entire UNIX community is thrilled that legal (and legible!!) copies are now available. An international “who’s who” of UNIX wizards, including Dennis Ritchie and Ken Thompson, the two earliest developers of UNIX, have contributed essays extolling the merits and importance of this underground classic. Besides being as chic as a computer book can be, Lions’ book remains of tremendous technical interest.

[As of May 13, 2000, SCO was giving away free source licenses of UNIX 6th Edition (binaries were previously available)!! Thanks are due to both SCO and the PDP UNIX Preservation Society. All you need is a PDP (or VAX) emulator, obtainable at,, or]

About the Author

John Lions (New South Wales) was a Lecturer in Computer Science when an early version of UNIX arrived at the University of New South Wales in 1974. He wrote his commentary as an Operating Systems text for his students in 1977 but was never permitted to have it published commercially during his working life. John died in December 1998, after this edition finally came out.

US bookstores carrying Lions’ Commentary on UNIX include: