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发信人: netiscpu (说不如做), 信区: Linux
标 题: [B] Red Hat Linux Unleashed (1)
发信站: 紫 丁 香 (Sat Jul 25 03:02:08 1998), 转信
Introduction to Linux
_________________________________________________________________
# What This Book Is Not
o What Is Linux?
# How to Pronounce Linux
# Linux Versus UNIX
o What Do I Get with a Linux System?
o The Downside of Linux and the Reason for This Book
o About Linux's Copyright
o Hardware Requirements
# Other Hardware Requirements
# Special Requirements for X
o Before You Get Started
o Summary
_________________________________________________________________
1
Introduction to Linux
Welcome to Linux.
This book is about Linux, a clone of the UNIX operating system that
runs on machines with an Intel 80386 processor or better, as well as
Intel-compatible CPUs, such as AMD and Cyrix.
This first chapter introduces you to the major features of Linux and
helps get you acquainted with them. It does not go into great detail
or cover any advanced topics, as this is done in later chapters.
Instead, it is intended to give you a head start in understanding what
Linux is, what Linux offers you, and what you need to run it.
Don't be afraid to experiment. The system won't bite you. You can't
destroy anything by working on it. UNIX has some amount of security
built in, to prevent "normal" users (the role you will now assume)
from damaging files that are essential to the system. The absolute
worst thing that can happen is that you'll delete all of your files
and have to go back and reinstall the system. So, at this point, you
have nothing to lose.
One word of caution when reading this chapter: At times it will delve
into topics that may seem very alien to you, especially if you are new
to UNIX and Linux. Don't despair. As you go through this book, you
will become more and more familiar with the topics introduced here.
Linux is not an easy system to pick up in one day, so don't try to do
it. There is no substitute for experience, so relax and learn Linux at
your own pace.
What This Book Is Not
This book makes several assumptions about you, the reader. I hope we
can safely assume that you have some working knowledge of PCs and
Microsoft's Disk Operating System (MS-DOS). (In some Linux
documentation, MS-DOS is also referred to as "messy DOS," but I'll let
you be the judge of that!) If you are not familiar with DOS or
computers in general, now would be a good time to pick up a book to
introduce yourself to PCs. Even so, you should be able to follow this
book without needing any extra material.
Some readers of this book will be familiar with UNIX. If that's the
case, a lot of the early material will be familiar to you, especially
when we talk about the shells. If you are new to UNIX, don't be
concerned: This book was written with you in mind and should guide you
through your early hesitant sessions at the console and show you
everything you need to know. Pretty soon, you'll be an expert! Now,
let's get started with Linux.
What Is Linux?
Linux is a free, UNIX work-alike designed for Intel processors on PC
architecture machines. Linux is not UNIX, as UNIX is a copyrighted
piece of software that demands license fees when any part of its
source code is used. Linux was written from scratch to avoid license
fees entirely, although the operation of the Linux operating system is
based entirely on UNIX. It shares UNIX's command set and
look-and-feel, so if you know either UNIX or Linux, you know the
other, too.
Linux supports a wide range of software, from TeX (a text formatting
language) to X (a graphical user interface) to the GNU C/C++ compilers
to TCP/IP networking. Linux is also compliant with the POSIX.1
standard, so porting applications between Linux and UNIX systems is a
snap.
New users of UNIX and Linux may be a bit intimidated by the size and
apparent complexity of the system before them. There are many good
books on using UNIX out there, for all levels of expertise ranging
from novice to expert. However, few (if any) of these books cover,
specifically, the topic of using Linux. Although 95 percent of using
Linux is exactly like using other UNIX systems, the most
straightforward way to get going on your new system is with a book
tailored for Linux (such as this one, amazingly enough!).
How to Pronounce Linux
Pronouncing the word Linux is one of the great controversies of the
Linux world. Americans pronounce the proper name Linus with a long i
sound, as in style. However, because Linux was originally based on a
small, PC-based implementation of UNIX called Minix (pronounced with a
short i), the actual pronunciation of Linux preserves this
characteristic: It's officially pronounced "LIH nucks."
Linux Versus UNIX
UNIX is a trademark of X/Open. Linux is not a trademark, and has no
connection to the trademark UNIX or X/Open.
UNIX is one of the most popular operating systems worldwide because of
its large support base and distribution. It was originally developed
as a multitasking system for minicomputers and mainframes in the
mid-1970s, but it has since grown to become one of the most widely
used operating systems anywhere, despite its sometimes confusing
interface and lack of central standardization.
UNIX is a multitasking, multiuser operating system. This means that
there can be many people using one computer at the same time, running
many different applications. (This differs from MS-DOS, where only one
person can use the system at any one time.)
Under UNIX, for users to identify themselves to the system, they must
log in, which entails two steps: Entering your login name (the name by
which the system identifies you), and entering your password, which is
your personal secret key to logging in to your account. Because only
you know your password, no one else can log in to the system under
your username.
In addition, each UNIX system has a hostname assigned to it. It is
this hostname that gives your machine a name, gives it character,
class, and charm. The hostname is used to identify individual machines
on a network, but even if your machine isn't networked, it should have
a hostname.
Versions of UNIX exist for many systems, ranging from personal
computers to supercomputers. Most versions of UNIX for personal
computers are quite expensive and cumbersome. Where does Linux fit in?
Well, Linux is free (solves the expensive part), very powerful, and
easy to install and maintain by an individual (so much for the
cumbersome part).
What Do I Get with a Linux System?
Linux is a freely distributable version of UNIX developed primarily by
Linus Torvalds at the University of Helsinki in Finland. Linux was
further developed with the help of many UNIX programmers and wizards
across the Internet, allowing anyone with enough know-how and gumption
to hack a custom UNIX kernel the ability to develop and change the
system.
UNIX and its clones have long been perceived as large,
resource-hungry, disk-devouring systems. Linux is not such a beast. It
is small, fast, and flexible.
Linux has been publicly available since around November of 1991. v0.10
went out in November of 1991, v0.11 in December of 1991. There are
very few small bugs now, and in its current state Linux is mostly
useful for people who are willing to port code and write new code.
Because Linux is very close to a reliable and stable system, Linus
decided that v0.13 will be known as v0.95.
So what are some of the important features of Linux that make it so
unique? Here are a few:
* Full multitasking and 32-bit support. Linux, like all other
versions of UNIX, is a real multitasking system, allowing multiple
users to run many programs on the same system at once. Linux is
also a full 32-bit operating system, utilizing the special
protected-mode features of Intel 80386 and later processors and
their work-alikes.
* The X Window System. The X Window System is the de facto
industry-standard graphics system for UNIX machines. A complete
version of the X Window System, known as XFree86, is available for
Linux. The X Window System is a very powerful graphics interface,
supporting many applications.
* TCP/IP (Transmission Control Protocol/Internet Protocol) support.
This is the set of protocols that links millions of university and
business computers into a worldwide network known as the Internet.
With an Ethernet connection, you can have access to the Internet
or to a local area network from your Linux system. Using SLIP
(Serial Line Internet Protocol) or PPP (Point to Point Protocol),
you can access the Internet over phone lines with a modem.
* Virtual memory and shared libraries. Linux can use a portion of
your hard drive as virtual memory, expanding your total amount of
available RAM. Linux also implements shared libraries, allowing
programs that use standard subroutines to find the code for these
subroutines in the libraries at runtime. This saves a large amount
of space on your system; each application doesn't store its own
copy of these common routines.
* The Linux kernel uses no code from AT&T or any other proprietary
source. Much of the software available for Linux is free. In fact,
a large number of utilities in Linux are developed by the GNU
project at the Free Software Foundation in Cambridge,
Massachusetts. However, Linux enthusiasts, hackers, programmers,
and recently even commercial companies from all over the world
have contributed to the growing pool of Linux software.
* Linux supports (almost) all of the features of commercial versions
of UNIX. In fact, some of the features found in Linux may not be
available on other proprietary UNIX systems.
* GNU software support. Linux supports a wide range of free software
written by the GNU Project, including utilities such as the GNU C
and C++ compiler, gawk, groff, and so on. Many of the essential
system utilities used by Linux are GNU software.
* Linux is compatible with the IEEE POSIX.1 standard. Linux has been
developed with software portability in mind, thus supporting many
important features of other UNIX standards.
* Virtual memory support. Linux utilizes all of your system's
memory, without memory limits or segmentation through the use of a
virtual memory manager.
* Built-in support for networking, multitasking, and other features.
You'll see this touted as "New Technology" in systems such as
Windows NT. In fact, UNIX (and now, Linux) has implemented this
"new technology" for more than 15 years.
* Linux is cheaper to get than most commercially available UNIX
systems and UNIX clones. If you have the patience and access to
the Internet, the only price you pay for Linux is your time. Linux
is freely available on the Internet. For a nominal fee of anywhere
from US $30 to US $90, you can save yourself some time and get
CD-ROM or floppy-disk distributions from several commercial
vendors (or from this book).
Arguably, the most important advantage of using Linux is that you get
to work with an honest-to-goodness kernel. All of the kernel source
code is available for Linux, and you have the ability to modify it to
suit your needs. Looking at the kernel code is an educational
experience in itself.
Undoubtedly, the development of Linux has been so rapid because of the
availability of the source code. Also, with an ever-expanding group of
hackers who want to get their hands dirty with their own system, Linux
has grown steadily into the fully packed operating system that it is
today.
______________________________________________________________
NOTE: Linux uses the Intel 80386 chip's protected mode-functions
extensively, and is a true 32-bit operating system. CPUs before the
80386 will not run Linux as they lack protected modes.
______________________________________________________________
The Downside of Linux and the Reason for This Book
Linux is a hacker's project, written by a multitude of gifted
programmers for the sheer joy of programming and sharing the code.
This hacker attitude can be a daunting experience for someone not
familiar with UNIX, and its side effects are sometimes noticed quite
easily (such as a lack of documentation, obtuse commands, and
dependencies on other programs that are not clear). Luckily, there is
little problem with stable Linux software because it has been worked
on by many people; it's the early releases of new software that tend
to show these holes.
Help with Linux is generally not a phone call away as it is with a
commercial version of UNIX. You can get help from the Internet
newsgroups and other members of the Linux community via e-mail.
However, when it's midnight and your system just won't boot like the
README file said it would, you do feel a sense of despair.
There is a huge distinction between commercial versions of UNIX and
Linux: Commercial versions of UNIX are designed for customers and will
work out of the box, whereas Linux is not guaranteed to work at all on
your system. You are indeed on your own.
Actually, the only problem for new users is a lack of basic UNIX
system-administrative knowledge. Setting up and running your own UNIX
system is something most UNIX users never get to do, even after years
of experience. Yes, you get to do it yourself, but it ain't that easy.
You might actually consider being nice to your local UNIX system
administrator after installing Linux for the first time.
Here are some other parts of Linux that you should be warned about:
* Some of the features on your favorite UNIX system may not be
available for your Linux system. Your choice in this matter is to
either write the application yourself, convince someone else to
write it, or find an alternative process (the easiest out in most
cases).
* As with software, some of the hardware in your machine may not be
supported by Linux. Again, your choices are to either write the
driver software yourself or get it from somewhere else.
* You do have to spend some time and effort managing your Linux
machine. You do develop a knack for fixing problems from
experience. However, only with experience can you learn to
recognize common problems and find or develop solutions.
Even with standard Linux distributions, there are sometimes little
quirks that need to be fixed by hand in order for everything to work
correctly. If you have previous UNIX experience, it should be easy to
find these problems. However, if you're new to UNIX, it would serve
you well to read up on using and running a UNIX system before you dive
in.
To reiterate, Linux isn't for everyone. Many users can get in over
their heads when starting with Linux. To keep your head above water, I
strongly encourage you to find a good book on using UNIX system
administration.
About Linux's Copyright
Ah, yes—that old topic of copyrights. Compared to death and
taxes, Linux copyrights are a mere annoyance.
Actually, Linux is copyrighted under the GNU General Public License,
sometimes called the GPL or copyleft. (Note the left instead of
right.) This copyleft license was developed by the Free Software
Foundation to enable programmers to write "free software," where
"free" refers to freedom, not just cost. The GPL provides for the
protection of such free software in a number of ways:
* It allows the original author to retain the software's copyright.
* It allows others to take the software and modify it, or even base
other programs on it.
* It allows others to redistribute or resell the software, or
modified versions of the software. Note that you can even resell
the software for profit. However, in reselling or redistributing
the software, you cannot restrict any of these rights from the
party you're selling it to.
______________________________________________________________
NOTE: Also, if you sell the software, you have to be able to
provide at no cost the full source code so that others can modify
the software and resell it if they wish. You cannot hold back the
source of your modifications.
______________________________________________________________
The original authors of the Linux software may never see a dime of
these revenues. This is allowed by the GNU GPL because the point of
free software isn't to make money. This is simply an understanding
between the authors of the software and those using or selling it.
One other thing: Free software, as covered by the GNU GPL (which
includes Linux), comes with absolutely no warranty. However,
individual vendors may provide support for the software, which usually
includes a warranty. Unless you purchased such support, the assumption
is that the software comes with no such warranty, and if you use a
piece of free software that goes haywire and wipes everything on your
system, neither the authors nor those who distributed the software to
you are liable.
Free software as covered by the GPL is not shareware, nor is it in the
public domain. Neither of these terms correctly describes what free
software really is. The complete GNU GPL is printed in Appendix E,
"Copyright Information." To sum it all up, you can freely distribute
Linux as much as you like, and you can even modify it and distribute
your own version of Linux. But in doing so, you can't take away those
rights from others. In short, you must attribute the original authors
of the work.
______________________________________________________________
NOTE: Please note that there are absolutely no warranties with any
of the software you get with Linux. If an application goes awry and
wipes your disk, you have no one's neck to wring. Unless someone
explicitly gives you a warranty in writing on their software, do
not assume any warranty whatsoever for anything other than what is
explicitly written in the warranties.
______________________________________________________________
Hardware Requirements
Now that you know a little about the good and bad points of Linux,
let's see what's required in terms of hardware.
Unlike some other versions of UNIX for the PC, Linux is very small.
You can run an entire system from a single, high-density 5.25-inch
floppy. However, to run a complete Linux system, there are other
hardware requirements.
Linux, by its very nature, is continuously expanding, and more
features are added every day. However, hardware compatibility is
limited to that hardware the developers themselves have access to. For
instance, if none of the Linux developers has access to the WhizBang
Slice-O-Matic T3222 Ethernet card from a no-name manufacturer, then
chances are it isn't supported.
On the other hand, there are many generic drivers for hardware, such
as the IDE disk driver, which should work with all IDE hard drives and
adapters regardless of manufacturer. Of course, the developers of the
drivers couldn't test their software against every IDE device on the
market, so they assume the IDE standards are followed by
manufacturers. If a device doesn't work, it's probably because the
manufacturer deviated from the standards, or added features the
generic drivers can't handle.
A good place to look on the CD-ROM is in the /docs/howto directory for
the Hardware-HOWTO file. This file will list a lot of the supported
hardware for Linux.
If your favorite peripheral isn't supported by Linux, all that's
required is to write a kernel driver for it. This may be easy or
difficult, depending on the hardware and the technical specifications
that are available. For example, some hardware developers prefer to
write their own drivers for MS-DOS and Windows, and not release
specifications for third parties to write their own. Therefore,
writing drivers for Linux will be difficult, if not impossible.
The following is a rough guideline of some hardware requirements for
Linux. You do not have to follow them directly, but this list should
give you a rough idea of what's required:
______________________________________________________________
NOTE: If you're in the market for a new system, you should heed the
following recommendations.
______________________________________________________________
* An Intel 80386 or better CPU (the faster and more powerful the
better, of course). You don't need a math coprocessor, although
it's strongly recommended as it speeds up a lot of graphics
operations, especially under X. If you have an 80386 chip, 80387
math coprocessors are available separately and are installed in a
socket on your motherboard. If you have a 80486 processor, the
math coprocessor is on the 486 chip itself. (The exception is the
80486SX, which is a 486 chip without the coprocessor components.)
Pentium and Pentium Pro CPUs have the coprocessor built in.
* If you don't have a math coprocessor, the Linux kernel will
emulate floating-point math for you. If you do have one, however,
floating-point math will be handled by the hardware, which for
some applications is a real plus.
* Your system must be either an ISA, EISA, PCI, or local bus
architecture machine. These terms specify how the CPU communicates
with hardware, and are a characteristic of your motherboard. Most
existing systems use the ISA bus architecture.
______________________________________________________________
NOTE: MicroChannel architecture (MCA) machines, such as the IBM
PS/2 line, are not currently supported.
______________________________________________________________
* At least 4MB of RAM.
* Memory is speed, so if you have more RAM you'll thank yourself for
it later. If you're a power user, 8MB should be more than enough
for most applications. If you want to run X Window, your system
will require at least 8MB of RAM.
* A hard drive with space available for installing Linux. The amount
of space required depends on the amount of software you're
installing and how much free space you wish to leave yourself. You
can install Linux in very small amounts of disk space, but a
realistic minimum is about 150MB. For a full system with X and
development tools, much more is required. The complete
installation can use up 250MB, with more useful for data files.
* A Hercules, CGA, EGA, VGA, or Super VGA video card and monitor. In
general, if your video card and monitor work under MS-DOS or
Microsoft Windows, then Linux should be able to use them without
any problem. However, if you're going to use the X Window system
(either Metro-X or Xfree86), some video configurations are not
supported.
Other Hardware Requirements
Linux will also run on a number of laptop machines (some laptops use
certain software interrupts to power the memory, and Linux doesn't
work well with these systems to date). The best way to find out if
Linux will run on your hardware is just to try it out.
______________________________________________________________
NOTE: At the time of writing, Linux doesn't run on an IBM PS/2
computer. Stay tuned to the Internet for details.
______________________________________________________________
There are other hardware drivers currently under development for
Linux. To use these drivers, however, you usually have to patch them
into your kernel code, which assumes that you already have a running
Linux system (a kind of chicken-and-egg problem if you have not
already installed Linux). In such cases, you can install whatever
Linux you happen to have and then apply the patches with the Linux
patch command.
Then there is the issue of tape drives for Linux. There is a working
QIC-02 device driver for Linux, supporting Everex/Wangtek cards. There
are additional patches for the QIC-02 to support Archive SC402/499R.
You can find them in /pub/linux/alpha/qic-02 directory at
tsx-11.mit.edu server. (There have been reports of some bugs in the
driver, but you can back up and restore.)
Most of the newer tape drivers are all for SCSI drives, so if you have
a SCSI tape drive, chances are that it is supported.
Special Requirements for X
Your 4MB of RAM will make X run very slowly. You should have at least
8MB of RAM for running programs in X. You will need another 6MB to
10MB of disk space for the GCC compiler in addition to X if you want
to develop applications for X.
______________________________________________________________
NOTE: Do not try to bring up an Xserver that does not support your
hardware. There have been cases where damage has resulted from
pushing the monitor (especially fixed-frequency monitors) beyond
its capabilities.
______________________________________________________________
As far as mice go, Linux supports both serial and Bus varieties. For
the serial mice, you can use Logitech, Microsoft, MouseSystems, or
compatibles. The following Bus mice are known to work: Logitech,
Microsoft, ATI_XL, and PS/2 (aux).
There you have it, a brief introduction to an operating system that
could very well change the way you program. Now for getting yourself
ready for Linux.
Before You Get Started
Assuming that you have hardware compatible with Linux, obtaining and
installing the system is not difficult. But be prepared to be a bit
frustrated at first, if you are new to UNIX or Linux. The two best
defenses against frustration with using Linux are the following:
1. Get organized.
2. Educate yourself about Linux and UNIX.
______________________________________________________________
NOTE: Experience with my bad memory has forced me to keep an
indexed log of all the bugs, quirks, and symptoms in Linux. I have
a dog-eared notebook of all the weird features of Linux.
______________________________________________________________
Summary
In this chapter we learned about Linux and some of its more prominent
features:
* UNIX is a trademark of X/Open. Linux is not a trademark, and has
no connection to the trademark UNIX or X/Open.
* Linux is designed to run on Intel 80386 and faster CPUs and their
compatibles.
* Linux has most of the UNIX-like features and applications built in
to it. These features include a Virtual File System (VFS),
networking, multitasking and multiuser capabilities along with a
host of applications such as Xfree86, Metro-X, TeX, and the GNU
utilities.
* You will learn a lot about operating systems when working with
Linux.
* Linux is copyrighted under the GNU copyleft agreement. See
Appendix E for the complete text.
* The hardware requirements for Linux include at least an 80386
processor, a minimum of 100MB of disk space, 4MB of RAM and a
3.5-inch floppy drive.
* The more memory you have, the faster Linux will run.
* The swap space on Linux is an area on the disk used by Linux as a
scratch area when working with lots of processes.
* You will need 8MB of RAM to get X Window to run with an acceptable
degree of performance.
* You will need to educate yourself a little on Linux and UNIX
before you start the installation procedure. This is especially
important if you are new to UNIX.
* There are several ways of finding help on topics in Linux: The
Linux Documentation Project, via FAQs, INFO-SHEETS, and from the
files on the CD-ROM itself.
* The Hardware-HOWTO document contains a lot of information about
all the devices supported by Linux.
It's best to check the Linux Hardware Compatibility List on the CD-ROM
before starting your installation process or buying anything for your
PC.
Previous Page Page Top TOC Next Page See Page
--
Enjoy Linux!
-----It's FREE!-----
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