More and more, people find themselves taking care of multiple computers, often from more than one manufacturer; it's quite rare to find a system administrator who is responsible for only one system (unless he has other, unrelated duties as well). While Unix is widely lauded in marketing brochures as the "standard" operating system "from microcomputers to supercomputers" and I must confess to having written a few of those brochures myself this is not at all the same as there being a "standard" Unix.At this point, Unix is hopelessly plural, and nowhere is this plurality more evident than in system administration. Before going on to discuss how this book addresses that fact, let's take a brief look at how things got to be the way they are now.
Figure P-1 attempts to capture the main flow of Unix development. It illustrates a simplified Unix genealogy, with an emphasis on influences and family relationships (albeit Faulknerian ones) rather than on strict chronology and historical accuracy. It traces the major lines of descent from an arbitrary point in time: Unix Version 6 in 1975 (note that the dates in the diagram refer to the earliest manifestation of each version). Over time, two distinct flavors (strains) of Unix emerged from its beginnings at AT&T Bell Laboratories which I'll refer to as System V and BSD but there was also considerable cross-influence between them (in fact, a more detailed diagram would indicate this even more clearly).
Figure P-1. Unix genealogy (simplified)
For a Unix family tree at the other extreme of detail, see http://perso.wanadoo.fr/levenez/unix/. Also, the opening chapters of Life with UNIX, by Don Libes and Sandy Ressler (PTR Prentice Hall), give a very entertaining overview of the history of Unix. For a more detailed written history, see A Quarter Century of UNIX by Peter Salus (Addison-Wesley).
The split we see today between System V and BSD occurred after Version 6. developers at the University of California, Berkeley, extended Unix in many ways, adding virtual memory support, the C shell, job control, and TCP/IP networking, to name just a few. Some of these contributions were merged into the AT&T code lines at various points.
System V Release 4 was often described as a merger of the System V and BSD lines, but this is not quite accurate. It incorporated the most important features of BSD (and SunOS) into System V. The union was a marriage and not a merger, however, with some but not all characteristics from each parent dominant in the offspring (as well as a few whose origins no one is quite sure of).
The diagram also includes OSF/1.
In 1988, Sun and AT&T agreed to jointly develop future versions of System V. In response, IBM, DEC, Hewlett-Packard, and other computer and computer-related companies and organizations formed the Open Software Foundation (OSF), designing it with the explicit goal of producing an alternative, compatible, non-AT&T-dependent, Unix-like operating system. OSF/1 is the result of this effort (although its importance is more as a standards definition than as an actual operating system implementation).
The proliferation of new computer companies throughout the 1980s brought dozens of new Unix systems to market Unix was usually chosen as much for its low cost and lack of serious alternatives as for its technical characteristics and also as many variants. These vendors tended to start with some version of System V or BSD and then make small to extensive modifications and customizations. Extant operating systems mostly spring from System V Release 3 (usually Release 3.2), System V Release 4, and occasionally 4.2 or 4.3 BSD (SunOS is the major exception, derived from an earlier BSD version). As a further complication, many vendors freely intermixed System V and BSD features within a single operating system.
Recent years have seen a number of efforts at standardizing Unix. Competition has shifted from acrimonious lawsuits and countersuits to surface-level cooperation in unifying the various versions. However, existing standards simply don't address system administration at anything beyond the most superficial level. Since vendors are free to do as they please in the absence of a standard, there is no guarantee that system administrative commands and procedures will even be similar under different operating systems that uphold the same set of standards.
Unix Versions Discussed in This Book
How do you make sense out of the myriad of Unix variations? One approach is to use computer systems only from a single vendor. However, since that often has other disadvantages, most of us end up having to deal with more than one kind of Unix system. Fortunately, taking care of n different kinds of systems doesn't mean that you have to learn as many different administrative command sets and approaches. Ultimately, we get back to the fact that there are really just two distinct Unix varieties; it's just that the features of any specific Unix implementation can be an arbitrary mixture of System V and BSD features (regardless of its history and origins). This doesn't always ensure that there are only two different commands to perform the same administrative function there are cases where practically every vendor uses a different one but it does mean that there are generally just two different approaches to the area or issue. And once you understand the underlying structure, philosophy, and assumptions, learning the specific commands for any given system is simple.
When you recognize and take advantage of this fact, juggling several Unix versions becomes straightforward rather than impossibly difficult. In reality, lots of people do it every day, and this book is designed to reflect that and to support them. It will also make administering heterogeneous environments even easier by systematically providing information about different systems all in one place.
Figure P-2. Unix versions discussed in this book
The Unix versions covered by this book appear in Figure P-2, which illustrates the influences on the various operating systems, rather than their actual origins. If the version on your system isn't one of them, don't despair. Read on anyway, and you'll find that the general information given here applies to your system as well in most cases.
The specific operating system levels covered in this book are:
This list represents some changes from the second edition of this book. We've dropped SCO Unix and IRIX and added FreeBSD. I decided to retain Tru64 despite the recent merger of Compaq and Hewlett-Packard, because it's likely that some Tru64 features will eventually make their way into future HP-UX versions.
When there are significant differences between versions, I've made extensive use of headers and other devices to indicate which version is being considered. You'll find it easy to keep track of where we are at any given point and even easier to find out the specific information you need for whatever version you're interested in. In addition, the book will continue to be useful to you when you get your next, different Unix system and sooner or later, you will.
The book also covers a fair amount of free software that is not an official part of any version of Unix. In general, the packages discussed can be built for any of the discussed operating systems.