UNIX: A Practical Definition

There's no such thing as UNIX. I realize this is a strange statement to make at the beginning of a book purporting to be about "UNIX System Security." UNIX has been around for a long time -- over 30 years as of this writing. During these decades, it has been metamorphosed millions of times, if not billions of times, by many thousands of individuals and companies implementing thousands of variants or "flavors," and by millions of system administrators installing it on everything from tiny embedded devices to supercomputers. Arguably, no two instances of the UNIX operating system are exactly the same.

Some of the drift in the meaning of UNIX is due to legal quandaries; some of it is the result of various commercial "UNIX wars" that have been waged over the years; some of it results from battles of wit and mind, with superior but unorthodox technologies winning over inferior authorized ones.

Given the polymorphous essence of UNIX, I'll start with a few different ways of looking at it and then shed some additional light by reviewing UNIX history. Here are several working definitions of UNIX:

• Legal -- While there may be no such thing as "UNIX," the term is a trademark owned by the Open Group, an international consortium that demands the mark receive proper attribution.¹ Repeat after me: "UNIX is a registered trademark of The Open Group." You'll sometimes see AT&T, Bell Labs, Novell, or X/Open Company Ltd. listed as the trademark holders -- it's been passed off time and again. Arguably, the mark has been diluted to the point of meaninglessness. Nonetheless, the Open Group promulgates "The Single UNIX® Specification" which can be viewed at http://www.UNIX-systems.org/online.html
• Technical -- According to the UNIX FAQ, UNIX is "an operating system typically written in C, with a hierarchical file system and integration of file and device I/O, whose system call interface includes services such as fork() and pipe() , and whose user interface includes tools such as cc , troff , grep , awk , and a choice of shell."² I might add that UNIX provides a consistent approach to multitasking, with built-in operations for the creation, synchronization, and termination of processes. It is intrinsically portable between different kinds of computers.
• Linguistic -- The name "Unix" was intended as a pun on the name Multics and was written "Unics" at first, for UNiplexed Information and Computing System. Both "Unix" and "UNIX" are in wide use today. At one point, Dennis Ritchie tried to promulgate the lower-case version, since "UNIX" isn't an acronym. In deference to the trademark, this text uses "UNIX."
• Social -- Many people who run UNIX-like systems such as Linux think they're running UNIX. Official UNIX systems and unofficial UNIX systems are commonly treated as belonging to a single category -- in books, in media coverage, on the net, and by general social consensus.