UNIX | Preface
Even though this book
deals with an operating system in particular, it will help you understand
operating systems in general. This fourth edition was written with this
objective in mind. In fact, theoretical courses on operating systems often use
the UNIX system to illustrate key features. Although we haven’t seen another
notable system since the advent of UNIX, it shouldn’t surprise us if future
operating systems adopt many of the key features of UNIX.
Many people derive
comfort from the “user-friendliness” offered by Windows. Why key in a command
when one or two mouse clicks can do the job? True, but it doesn’t require much
effort for a UNIX enthusiast to prove that the mouse can’t solve all problems.
Once you go through Part I of this book, you’ll discover several situations
where complex jobs are handled—not by mouse clicks—but by combining tools and
programming with the shell. Shun the herd and join the select body of people
for whom it doesn’t matter whether UNIX is user-friendly or not. It’s simply a
way of life—a life they will never cease to cherish.
Why
UNIX Still Remains Important
Even though UNIX was
created by the engineering and scientific community, its robustness and absence
of a comparable alternative led to its widespread acceptance in the commercial
market. UNIX today runs with full vigor on both handhelds and supercomputers.
It remains the preferred platform for enterprise databases, ISPs, Web servers
and electronic commerce. Further, UNIX is getting better all the time simply
because numerous minds spread across the globe are engaged in its improvement and enhancement. Think big and you’ll have to think of UNIX.
UNIX
fragmentation—once a major irritant—has now been addressed by standards bodies
like POSIX and The Open Group. Today, we have a single standard, The Single
UNIX Specification, that lays down once and for all what an operating system
must offer to be called UNIX. This single reference allows you to develop
applications that will run without modification on all UNIX systems. We
constantly refer to POSIX in this text.
This
Fourth Edition
This edition contains
fewer chapters but retains the page count. I am of the view that UNIX system
administration deserves a separate book by itself, and have, therefore, pruned
its coverage in this edition. Also, TCP/IP and networking aren’t exactly part
of basic UNIX, the reason why there’s only a single chapter on networking tools
this time. Network administration along with related topics have been moved to
the Web site. The remaining key features of this edition are described below:
- Numerous asides, entitled How It Works, that
explain how a key concept works in UNIX. Even though these asides are for
optional reading, they provide a fuller understanding as well as the base
for programming in UNIX.
- A separate chapter, Program Development Tools,
that includes make and version control (SCCS and RCS). If
you are working on large projects, then you need to use this chapter for
program maintenance.
- Coverage on cryptography and the tools offered
by the Secure Shell suite (SSH). As hackers increasingly threaten the way
we live and transact, you need to know why and how data is encrypted.
- A separate command reference for the vi editor
as Appendix B. This should have been done much earlier, but now it’s
finally here.
- A specially compiled HOWTO (Appendix C) that
helps you locate a command sequence that does a specific job.
This book also
discusses Linux—not as an alternative to UNIX—but as an important UNIX
implementation. You must treat Linux as a gateway to learning UNIX. Like other
UNIX flavors like Solaris, HP-UX and AIX, Linux complies with POSIX and The
Single UNIX Specification. In fact, there are more similarities than
differences that Linux has with these flavors. This book doesn’t encourage the
use of Linux-specific features.
A note of caution at
this stage would be in order. Unfortunately, many people like UNIX/Linux for
its graphical user interface (GUI). You’ll have to understand that GUI use is
to be reserved for viewing graphics and browsing the Web. To use UNIX in
Windows-style would be self-defeating. If you appreciate that the UNIX command
line is the way to interact with the system, then this book is for you. Even
though the X Window system still features as a separate chapter in this
edition, its coverage would be curtailed in future editions.
The exercises at the
end of each chapter have been given a major facelift. There are more and
challenging exercises in this edition than in previous ones. The section
entitled Test Your Understanding contains mostly simple questions, but you
should try to solve them before you switch chapters. The answers to these
questions are available in Appendix D. The more involved questions feature in
Flex Your Brains, whose answers are provided on the book’s Web site, but available
only to adopters of the book.
All examples should
run on most UNIX/Linux systems, and you’ll find suitable indications when a
system-specific feature is encountered. Don’t forget to read Conventions
Followed in the Book before you move into the UNIX mainstream beginning with
Chapter 1. Key terms, now shown in a bold and bigger font, would be easier to
spot this time.
Acknowledgements
Vibha Mahajan has
always been a pleasure to work with, in this as well as in previous editions.
Jacob Alexander has never been found wanting in offering valuable suggestions,
and has lived up to my expectations very well. Thanks are also due to Mini
Narayanan for copy editing and Sohan Gaur for managing the production process.
My wife Julie and daughter Sohini continue to remain my main source of
inspiration.
And on this note, I
wish you an exciting journey to the UNIX world!
SUMITABHA DAS
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