| |
Linux is an operating system, a software program that
controls your computer. Most vendors load an operating system
onto the hard drive of a PC before delivering the PC, so,
unless the hard drive of your PC has failed, you may not
understand the function of an operating system.
An operating system solves several problems arising from
hardware variation. As you're aware, no two PC models (or
models of other computers, for that matter) have identical
hardware. For example, some PCs have an IDE hard drive,
whereas others have a SCSI hard drive. Some PCs have one hard
drive, others have two or more. Most PCs have a CD-ROM drive,
but some do not. Some PCs have an Intel Pentium CPU, whereas
others have an AMD K-6, and so on. Suppose that, in a world without
operating systems, you're programming a new PC application,
perhaps a new multimedia word processor. Your application must
cope with all the possible variations of PC hardware. As a
result, it becomes bulky and complex. Users don't like it
because it consumes too much hard drive space, takes a long
time to load, and - because of its size and
complexity - has more bugs than it should.
Operating systems solve this problem by providing a single
standard way for applications to access hardware devices. When
an operating system exists, applications can be more compact,
because they share the commonly used code for accessing the
hardware. Applications can also be more reliable because this
code is written only once, and by expert programmers, rather
than by every application programmers.
As you'll soon learn, operating systems do many other
things as well; for example, they generally provide a filesystem so that you can store and retrieve data, and a user
interface so that you can control the operation of your
computer. However, if you think of a computer's operating
system as its subconscious mind, you won't be far off the
mark. It's the computer's conscious mind - applications
such as word processors and spreadsheets - that do useful
work. But, without the subconscious - the operating
system - the computer would cease breathing and
applications would not function.
Now that you know what an operating system is, you may be
wondering what operating system your PC uses. Chances are,
your PC operating system was provided by Microsoft.
Table 1.1 shows the sales of several popular
desktop operating systems during 1997 and projected sales
for 2001.[] Bear in mind that, because
Linux is a free operating system, Linux sales are a mere
fraction of Linux installations. Moreover, unlike most
commercial operating systems, Linux is not sold under terms
of a per-seat license; a company is free to purchase a
single Linux CD-ROM diskette and install Linux on as many
computer systems as they like.
Table 1.1: Sales of Popular Desktop
Operating Systems
|
Operating System |
1997[] |
2001 (est.)[] |
|
Windows
95/98 |
69.4% |
65.0% |
|
Windows NT
Workstation |
9.2 |
26.2 |
|
DOS with Windows
3.x |
7.7 |
0.3 |
|
MacOS |
4.6 |
1.9 |
|
Linux |
2.4 |
4.2 |
|
DOS without
Windows |
2.3 |
0.3 |
|
Unix |
1.0 |
0.5 |
|
OS/2 Warp |
0.8 |
1.2 |
|
Other |
2.7 |
0.5 |
As the table shows, your desktop computer is probably
running Microsoft Windows 95 or Windows 98, which together
accounted for over 69% of 1997 sales. The sales of Linux
were miniscule in comparison: a mere 2.4%. As explained,
these figures don't do full justice to the ubiquity of
Linux. Nevertheless, notice that sales of Linux are expected
to almost double, whereas those of Windows 95/98 are
expected to slightly contract.
Later in this chapter you'll learn how Linux is
distributed, but recall that Linux was termed a
free operating system. If you have a
high-speed Internet connection, you can download, install,
and use Linux without paying anyone for anything (except
perhaps your Internet Service Provider, who may impose a
connection fee). It's anyone's guess how many people have
downloaded Linux, but estimates indicate that between 7 and
10 million computers run Linux.
Moreover, many Linux users run Linux not as a desktop
computer but as a server, which is powered up and on-online
24 hours per day, connected (at least occasionally) to the
Internet, and ready to provide services to requesting
clients. For example, many Linux users run web servers,
hosting web sites browsed by users worldwide. But, the
number of desktop Linux users - those who power on their
computer to use it and power it off when they're
done - is rising.
Desktop use of Linux is the focus of this book. However, if
you're unfamiliar with Linux and Unix, this book is right
for you even if you plan to establish a Linux server. This
book will take you through the basics of setting up and
using Linux. After you've mastered what this book offers,
you should consult
Running Linux, Third
Edition, Matt Welsh, Matthias Kalle Dalheimer and
Lar Kaufman (O'Reilly, 1999), a more advanced book that
focuses on setting up and using Linux servers.
Linux is distinguished from many popular operating
systems in three important ways.
-
Linux is a cross-platform operating system that runs
on many computer models. Only Unix, an ancestor of
Linux, rivals Linux in this respect. In comparison,
Windows 95 and Windows 98 run only on CPUs having the
Intel architecture. Windows NT runs only on CPUs having
the Intel architecture or the DEC Alpha.
-
Linux is free, in two senses. First, you may pay
nothing to obtain and use Linux. On the other hand, you
may choose to purchase Linux from a vendor who bundles
Linux with special documentation or applications, or who
provides technical support. However, even in this case,
the cost of Linux is likely to be a fraction of what
you'd pay for another operating system. So, Linux is
free or nearly free in an economic sense.
Second, and more important, Linux and many Linux
applications are distributed in source form. This makes
it possible for you and others to modify or improve
them. You're not free to do this with most operating
systems, which are distributed in binary form. For
example, you can't make changes to Microsoft Windows or
Microsoft Word - only Microsoft can do that. Because
of this freedom, Linux is being constantly improved and
updated, far outpacing the rate of progress of any other
operating system. For example, Linux will likely be the
first operating system to support Intel's forthcoming
Merced 64-bit CPU. -
Linux has attractive features and performance. Free
access to Linux source code lets programmers around the
world implement new features, and tweak Linux to improve
its performance and reliability. The best of these
features and tweaks are incorporated in the standard
Linux kernel or made available as kernel patches or
applications. Not even Microsoft can mobilize and
support a software development team as large and
dedicated as the volunteer Linux software development
team, which numbers in the hundreds of thousands,
including programmers, code reviewers, and
testers.
Linux traces its ancestry back to a mainframe
operating system known as Multics (Multiplexed Information
and Computing Service). Begun in 1965, Multics was one of
the first multi-user computer systems and remains in use
today. Bell Telephone Labs participated in the development
of Multics, along with the Massachusetts Institute of
Technology and General Electric.
Two Bell Labs software engineers, Ken Thompson and
Dennis Richie, worked on Multics until Bell Labs withdrew
from the project in 1969. One of their favorite pastimes
during the project had been playing a multi-user game called
Space Travel. Now, without access to a Multics computer,
they found themselves unable to indulge their fantasies of
flying around the galaxy. Resolved to remedy this, they
decided to port the Space Travel game to run on an otherwise
unused PDP-7 computer. Eventually, they implemented a
rudimentary operating system they named
Unics, as a pun on
Multics. Somehow, the spelling of the
name became
Unix.
Their operating system was novel in several respects,
most notably portability. Most previous operating systems
had been written for a specific target computer. Just as a
tailor-made suit fits only its owner, such an operating
system could not be easily adapted to run on an unfamiliar
computer. In order to create a portable operating system,
Ritchie and Thompson first created a programming language,
called
C. Like assembly language, C let
a programmer access low-level hardware facilities not
available to programmers writing in a high-level language
such as FORTRAN or COBOL. But, like FORTRAN and COBOL, a C
program was not bound to a particular computer. Just as a
ready-made suit can be lengthened or shortened here and
there to fit a purchaser, writing Unix in C made it possible
to easily adapt Unix to run on computers other than the
PDP-7.
As word of their work spread and interest grew,
Ritchie and Thompson made copies of Unix freely available to
programmers around the world. These programmers revised and
improved Unix, sending word of their changes back to Ritchie
and Thompson, who incorporated the best such changes in
their version of Unix. Eventually, several Unix variants
arose. Prominent among these was BSD (Berkeley Systems
Division) Unix, written at the University of California,
Berkeley, in 1978. Bill Joy, one of the principals of the
BSD project, later became a founder of Sun Microsystems,
which sold another Unix variant (SunOS) to power its
workstations. In 1984, AT&T, the parent company of Bell
Labs, began selling its own version of Unix, known as System
V.
What Ritchie and Thompson had begun in a distinctly
non-commercial fashion ended up spawning several legal
squabbles. When AT&T grasped the commercial potential
of Unix, it claimed Unix as its intellectual property and
began charging a hefty license fee to those who wanted to
use its Unix. Soon, others who had implemented Unix-like
operating systems were distributing licenses only for a
fee. Understandably, those who had contributed
improvements to Unix considered it unfair for AT&T and
others to appropriate the fruits of their labors. This
concern for profit was unlike the democratic,
share-and-share-alike spirit of the early days of
Unix.
Some, including MIT scientist Richard Stallman,
yearned for the return of those happier times and the
mutual cooperation of programmers that then existed. So,
in 1983, Stallman launched the GNU (GNU's not Unix)
project, which aimed at creating a free Unix-like
operating system. Like early Unix, the GNU operating
system was to be distributed in source form so that
programmers could read, modify, and redistribute it
without restriction. Stallman's work at MIT had taught him
that, by using the Internet as a means of communication,
programmers the world over could improve and adapt
software at incredible speed, far outpacing the fastest
rate possible using traditional software development
models, in which few programmers actually see one
another's source code.
As a means of organizing work on the GNU project,
Stallman and others created the Free Software Foundation
(FSF), a non-profit corporation that seeks to promote free
software and eliminate restrictions on the copying,
redistribution, understanding, and modification of
software. Among other activities, the FSF accepts
tax-deductible charitable contributions and distributes
copies of software and documentation for a small fee,
using this revenue to fund its operations and support the
GNU project.
If you find it peculiar that the FSF charges a
fee - even a small fee - for "free" software, you
should understand that the FSF intends the word
free to refer primarily to freedom,
not price. The FSF believes in three fundamental software
freedoms:
-
You can copy GNU software and give it away to
anyone you choose. -
If you're a programmer, you can modify GNU
software any way you like, because you have access to
the source code. -
You can distribute improved versions of GNU
software. However, you cannot charge anyone a fee for
using your improved version (although you can charge a
fee for providing a user with a physical copy of your
software).
Commercial software vendors protect their proprietary
rights to software by copyrighting the software. In
contrast, the FSF protects software freedom by
copylefting its software. If the FSF
placed its software in the public domain, others would be
free to transform it into a proprietary product, denying
users the freedom intended by the original author of the
software. For example, a company might distribute the
software in binary rather than source form and require
payment of a license fee for the privilege of making
additional copies.
To copyleft software, the FSF uses the same legal
instrument used by proprietary software vendors - the
copyright - but the FSF adds special terms that
guarantee freedom to users of the software. These terms,
referred to as the
GNU Public
License, give everyone the right to use,
modify, and redistribute the software (or any software
derived from it), but only if the distribution terms are
unchanged. Thus someone who attempts to transform FSF
software into a proprietary product has no right to use,
modify, or distribute the product. As the FSF puts it,
"Proprietary software developers use copyright to take
away the users' freedom; we use copyright to guarantee
their freedom. That's why we reverse the name, changing
copyright into
copyleft."
By the early 1990s, the FSF had obtained or written
all the major components of the GNU operating system
except for one: the kernel. About that time, Linus
Torvalds, a Finnish computer science student, began work
on a kernel for a Unix-like system. Linus had been working
with Minix, a Unix-like operating system written by Andrew
Tannenbaum primarily for pedagogical use. Linus was
disappointed by the performance of the Minix kernel and
believed that he could do better. He shared his
preliminary work with others on Internet newsgroups. Soon,
programmers around the world were working together to
extend and improve his kernel, which he called
Linux (for
Linus's
Minix). As
Table 1.2 shows,
Linux grew rapidly. Within three years of its October 5,
1991 initial release, Linux was released as production
software; version 1.0 was released in March of
1994. However, as early as 1992, Linux had been integrated
with other GNU software to produce a fully functional
operating system, which took as its name the name of its
kernel.
Table 1.2: The History of Linux
|
Year |
Version |
Users |
Kernel size
(Bytes) |
Milestone(s) |
|
1991 |
0.01 |
100 |
63,362 |
Linus Torvalds writes
Linux kernel |
|
1992 |
0.99 |
1000 |
431,591 |
GNU software integrated
with Linux kernel, producing a fully functional
operating system |
|
1993 |
0.99 |
20,000 |
937,917 |
High rate of code
contributions prompts Linus to delegate code
review responsibility |
|
1994 |
1.0 |
100,000 |
1,016,601 |
First production
release |
|
1995 |
1.2 |
500,000 |
1,850,182 |
Linux adapted to
non-Intel processors |
|
1996 |
2.0 |
1,500,000 |
4,718,270 |
Linux supports multiple
processors, IP masquerading, and Java |
|
1999 |
2.2 |
7,500,000 |
10,600,000[] |
Linux growth rate
exceeds that of Microsoft Windows
NT |
However, work on Linux did not cease. Since the
initial production release, the pace of development has
accelerated as Linux has been adapted to include support for
non-Intel processors and even multiple processors,
sophisticated TCP/IP networking facilities such as IP
masquerading, and more. Versions of Linux are now available
for such computer models as the Apple PowerPC, the DEC
Alpha, the Motorola 68k, the Sun SPARC, the Mips, and many
others. Moreover, Linux does not implement an obscure Unix
variant: it generally complies with the POSIX (Portable
Operating System Interface) standard that forms the basis of
the X/Open specifications of The Open Group.
Another important component of Linux is its graphical
user interface, the X Window System. Unix was originally a
mouseless, text-based system that used noisy teletype
machines rather than modern CRT monitors. The Unix command
interface is very sophisticated and, even today, some power
users prefer it to a point-and-click graphical environment,
using their CRT monitor as though it were a noiseless
teletype. Consequently, some remain unaware that Unix long
ago outgrew its text-based childhood, and now provides users
a choice of graphical or command interfaces.
The X Window System (or simply X) was
developed as part of the Massachusetts Institute of
Technology's (MIT) Project Athena, which it began in
1984. By 1988, MIT released X to the public. MIT has since
turned development of X over to the X Consortium, which
released version 6 in September 1995.
X is a unique graphical user interface in two major
respects. First, X integrates with a computer network,
letting users access local and remote applications. For
example, X lets you open a window that represents an
application running on a remote server: the remote server
does the heavy-duty computing; all your computer need do is
pass the server your input and display the server's
output.
Second, X lets you configure its look and feel to an
amazing degree. To do so, you run a special
application - called a
window
manager - on top of X. A variety of
window managers is available, including some that closely
mimic the look and feel of Microsoft Windows.
Because Linux can be freely redistributed, you can
obtain it in a variety of ways. Various individuals and
organizations package Linux, often combining it with free
or proprietary applications. Such a package that includes
all the software you need to install and run Linux is
called a
Linux distribution.
Table 1.3 shows some of the most popular
Linux distributions.
Caldera, Red Hat, Slackware, and SuSE are packaged by
commercial companies, which seek to profit by selling
Linux-related products and services. However, because
Linux is distributed under the GNU GPL, you can download
these distributions from the respective companies' web
sites or make additional copies of a Linux distribution
you purchase from them. (Note, however, that you cannot
necessarily make additional copies of proprietary software
that these companies may distribute with their Linux
distribution.) Debian GNU/Linux is the product of
volunteer effort conducted under the auspices of Software
In The Public Interest, Inc., a non-profit
corporation. This book is bundled with a copy of Debian
GNU/Linux, which you can install and run on your
PC.
The origins of Linux and the availability of its source code
set it apart from other operating systems. But most users
choose an operating system based on features and
performance - and Linux delivers these in spades.
Table 1.4 compares certain features and
performance characteristics of Linux with those of
Microsoft Windows NT 4.0 and Sun Microsystems Solaris
2.6.[] Each of these three operating
systems can be run on an Intel-architecture PC.
Table 1.4: Linux Features and
Performance Comparison
|
Characteristic |
Linux |
Windows NT |
Solaris |
|
Range of compatible
hardware |
Very wide |
Modest |
Narrow |
|
Minimal
hardware |
386 PC |
486 PC |
Pentium |
|
Representative cost of
hardware |
$200 |
$1300 |
$1600 |
|
Average
downtime |
Very low |
As low as 30
min./week |
Very low |
|
Performance |
High |
Comparable to
Linux |
Half of Linux to same as
Linux |
|
Multi-processing
capabilities |
Excellent |
Modest |
Excellent |
|
IP Security
(IPSec) |
Yes |
Planned |
1999 |
|
IPv6 |
Available |
Privately
demonstrated |
Beta |
|
Overall user satisfaction,
per
Datapro |
Highest |
Lowest |
Medium |
|
Source code readily
available |
Yes |
No |
No |
|
Installed
base |
Millions |
Millions |
Hundreds of
thousands |
As you can see, Linux fares well in this comparison. It
runs on a wider range of hardware platforms and runs
adequately on less costly and powerful systems. Moreover,
the typical downtime of a Linux system is less than that of
a Windows NT system and its performance surpasses that of a
Solaris system. Its multi-processing capabilities exceed
those of Windows NT and its support of advanced TCP/IP
networking facilities is superior to that of Windows NT and
Solaris. As a group, Linux users are more satisfied than
Windows NT users and Solaris users. Linux source code is
readily available. And, the Linux installed base dwarfs that
of Solaris and approaches that of Windows NT.
But this impressive inventory of selling points doesn't
end the matter. Let's consider some other technical
characteristics of Linux that distinguish it from the
pack. Foremost in the minds of many is the low cost of
Linux. Comparable server operating systems can cost more
than $100,000. The low cost of Linux makes it practical for
use even as a desktop operating system. In that mode, it
truly eclipses the competition.
Many desktop systems are occasionally, even regularly,
employed as servers. Because Linux was designed for use as a
server operating system, its features and performance
readily outshine those of desktop operating systems used as
makeshift servers. For example, Microsoft's software license
for Windows NT Workstation restricts the number of
simultaneous client connections to 10; if your Windows NT
Workstation computer accepts more than 10 client
connections, it is operating in breach of license. However,
Linux imposes no such restriction: your Linux desktop is
free to accept as many client connections as you think it
can handle.
Again, because it was designed as a server, Linux
provides more reliable data storage than competing desktop
operating systems. Most Linux users store their disk data
using the EXT2 filesystem, which is superior in performance
and reliability to filesystems (partition types) provided
by Microsoft operating systems, including FAT, FAT32, and
NTFS. Of course, Microsoft claims that its NTFS filesystem
is so reliable that you'll probably never need to use
special software tools to recover lost data - truth is,
Microsoft provides no such tools. Despite Microsoft's
ambitious claims, users report that NTFS reliability is not
perfect. Here's a case in point:
When my Windows NT Workstation computer crashed a
little over a year ago, I discovered that its NTFS file
system was damaged. I searched the Microsoft web site for
recovery instructions and tools and found nothing that
helped. So, I went to my local software store and
purchased a third party disk recovery tool for
Windows NT. When I opened the box, I was angered to
discover that it supported recovery of FAT and FAT32
data, but not NTFS data.
Eventually, I recovered 95 percent of my data by
using a free Linux utility that was able to open the
damaged NTFS partition and copy its files. If I'd been
without Linux, I'd be without my data.
Like other server operating systems, Linux provides
advanced disk management (RAID), which makes it possible to
automatically duplicate stored data on several hard
drives. This greatly improves the reliability of data
storage; if one hard drive fails, the data can be
read from another. Competing desktop operating systems such
as Microsoft Windows 95/98 do not support this capability
(though several third parties sell drivers that let you add
this capability to your desktop operating system).
If you're an old computer dog who remembers the days of
MS-DOS, you may have a fondness for what's now called the
MS-DOS Prompt window. However, if you've worked exclusively
within the Microsoft Windows point-and-click environment,
you may not fully understand what the MS-DOS Prompt window
is about. The MS-DOS Prompt window provides what's called a
command-line interface. By typing commands,
chosen from a list of commands the operating system
understands, you can direct the computer to perform a
variety of tasks.
For most users, the command interface is not as
convenient as the point-and-click interface offered by
Microsoft Windows. That's because you must know the commands
the operating system understands, and must type them
correctly, if you expect the operating system to do your
bidding.
However, the MS-DOS Prompt window lets you accomplish
tasks that would be cumbersome and time-consuming if
performed by pointing and clicking. Linux comes with a
similar command interface, known as the
shell. But, the word
"similar" fails to do justice to the
Linux shell's capabilities, because the MS-DOS command line
provides a fraction of the capabilities provided by the
Linux shell.
In particular, the MS-DOS command line lacks many
ease-of-use features found in the Linux shell. You may have
used the MS-DOS command line and, finding it distastefully
cumbersome, forever rejected it in favor of pointing and
clicking. If so, you'll be pleasantly surprised to see how
easy it is to use the Linux shell. You'll certainly be
pleased - perhaps amazed - by the enormous power it
offers. You'll learn more about the Linux shell in Chapter 4,
Issuing Linux Commands.
If you're a programmer, you'll also admire the ease with
which it's possible to develop portable, Unix-compliant
software by using Linux. Linux comes with a complete suite
of software development tools, including an assembler, C
compiler, C++ compiler,
make application,
and source code librarian. All of these are freely
distributable programs made available under the terms of the
GNU GPL.
 |
 |
 |
|
1.1 Linux at Home and at Work |
 |
1.3 Reasons to Choose or Not Choose Linux |
|
|
