Lions' Commentary on UNIX 6th Edition, with Source Code by John Lions (1976) contains the complete source code of the 6th Edition Unix kernel plus a commentary. It is commonly referred to as the Lions book. Despite its age, it is still considered an excellent commentary on simple but high quality code.

Peer-To-Peer Communications 1996 reissue

For many years, the Lions Book was the only Unix kernel documentation available outside Bell Labs. Although Bell would often make a copy available to anyone with a license covering 6th Edition Unix, it mainly spread by samizdat. It was commonly held to be the most copied book in computer science.

Synopsis

Unix Operating System Source Code Level Six is the source code, lightly edited by Lions to better separate the functionality — system initialization and process management, interrupts and system calls, basic I/O, file systems and pipes and character devices. All procedures and symbols are listed alphabetically with a cross reference.

The code as presented will run on a PDP-11/40 with RK-05 disk drive, LP-11 line printer interface, PCL-11 paper tape writer and KL-11 terminal interface, or a suitable emulator.

A Commentary on the Unix Operating System starts with notes on Unix and other useful documentation (the Unix manual pages, DEC hardware manuals and so on), a section on the architecture of the PDP-11 and a chapter on how to read C programs. The source commentary follows, divided into the same sections as the code. The book ends with suggested exercises for the student.

As Lions explains, this commentary supplements the comments in the source. It is possible to understand the code without the extra commentary, and the reader is advised to do so and only read the notes as needed. The commentary also remarks on how the code might be improved.

Publication history

The source code and commentary were originally produced in May 1976 as a set of lecture notes for Lions' computer science courses (6.602B and 6.657G) at the University of New South Wales. This was legally permissible as UNSW was a Unix licensee.

UNIX News March 1977 announced the availability of the book to Unix licensees. Lions had trouble keeping up with its popularity, and by 1978 it was only available from Bell Labs.

It was never formally published as Western Electric (AT&T) wished to maintain trade secret status on the kernel source. However, thousands of computer science students around the world spread photocopies. As they could not study it legally in class, they would sometimes meet after hours to discuss the book. Many pioneers of Unix and open source had a treasured multiple-generation photocopy.

Various Unix people, particularly Peter H. Salus, Dennis Ritchie and Berny Goodheart, lobbied Unix's various owners (AT&T, Novell, the Santa Cruz Operation) for many years to allow the book to be published officially. In 1996 SCO finally authorised the release of the twenty-year-old 6th Edition source code, and the full code plus the 1977 version of the commentary was published by Peer-To-Peer Communications (ISBN 1-57398-013-7). The reissue includes commentary from Michael Tilson (SCO), Peter Salus, Dennis Ritchie, Ken Thompson, Peter Collinson, Greg Rose , Mike O'Dell , Berny Goodheart and Peter Reintjes .

Review quote

After 20 years, this is still the best exposition of the workings of a "real" operating system — Ken Thompson, co-author of Unix

External links

• Peer-To-Peer Communications website
• Complete commentary in PDF, PostScript, and LaTeX formats
• Complete source code listing available in PDF and HTML formats (6th Edition Unix source code as modified by John Lions)
• Code Critic (Rachel Chalmers, Salon 30 Nov 1999)
• Ersatz 11 (commercial), SIMH (free), and other PDP-11 hardware emulators