Unix Defined

Possibly the only controversial thing in this book is my definition of Unix. Defining Unix has always been a bit of a challenge, something that true geeks will argue over for hours.

At one point, Unix ran only on exotic and expensive workstation and server hardware produced by an elite few companies. These days, you can run one or more flavors of free Unix on almost any kind of computer you can imagine.

Having worked for years at a company that makes a "Unix-like" microkernel operating system, I've been exposed to the POSIX standards that actually define, in excruciating detail, what a Unix system is and how it works.

My bold and controversial claim is that a "Unix" system is anything that implements these POSIX standards (specifically, POSIX 1003.1 and 1003.2), and I'll be covering four of these Unixen in this book.

Linux is a mishmash of features from other Unix systems, created because Linus Torvalds wanted a free operating system like Minix (a minimal Unix system used for teaching). Since then, Linux has been extended and expanded into one of the most popular Unix operating systems. Although it's never been officially tested or validated, it implements the POSIX APIs (application programming interfaces) and applications that define a Unix system.

FreeBSD is a direct descendant of the original BSD (Berkeley Software Distribution) Unix, and it has all of the POSIX programming APIs and command-line applications. Its "ports" system gives you access to almost every freely available Unix application in existence. FreeBSD is known for rock-hard stability and excellent network performance.

Many people view Microsoft Windows as the antithesis of Unix. Its DOS roots (and, with NT, 2000, and XP, its VMS roots) seem at odds with the power and elegance of a Unix system's command-line interface. Generally they're right, but there's still hope! Install Cygwin on Windows 2000 or Windows XP and you've suddenly got a very complete and capable Unix emulation layer implementing most if not all of the POSIX APIs and boasting a large collection of applications. Be careful about telling folks that you can run a Unix-like system on top of Windows, because pointing this out to some old-school Unix folks is a bit like telling kids about Santa.

When MacOS X was released, it suddenly became the world's most popular Unix desktop operating system. In fact, the GUI is so good, most Mac OS X users are never exposed to the BSD Unix layer lurking below. If Apple has somehow missed shipping a complete implementation of the POSIX applications, a third-party system called Fink makes it easy to add them to your Mac.

Any time I write "Unix," I mean any system that lets you write programs using the POSIX 1003.1 APIs, and that sports a command-line environment featuring a full suite of standard Unix applications (the POSIX 1003.2 commands). More specifically, I mean the four flavors of Unix we'll be looking at in this book: Fedora Core 3 Linux, FreeBSD 5.3, Cygwin, and Mac OS X.