ch01.htm

linux-unix130.linux.and.unix.ebooks130 linux and unix ebookslinuxLearning Linux - Collection of 12 E

<P>UNIX and its clones have long been perceived as large, resource-hungry, disk-chomping

systems. Linux is not such a beast. Linux is small, fast, and flexible.</P>

<P>Linux has been publicly available since about November 1991. Version 0.10 went

out at that time, and version 0.11 followed in December 1991. There are very few

small bugs now, and in its current state, Linux is most useful for people who are

willing to port and write new code. When Linux was very close to a reliable/stable

system, Linus decided that version 0.13 would be known as version 0.95. Believe it

or not, the whole story started with two processes that printed <TT>AAAA...</TT>

and <TT>BBBB...</TT> on a dumb terminal. Linus then expanded on this simple task-switching

mechanism and, with the help of many avid supporters, developed and released a stable,

working version of Linux.</P>

<P>So, what are some of the important features of Linux that make it unique? Here

are a few:



<UL>

	<LI>Full multitasking and 32-bit support. Linux, like all other versions of UNIX,

	is a real multitasking system, enabling multiple users to run many programs on the

	same system at once. The performance of a 100 MHz 486 system running Linux is comparable

	to many low- to medium-end workstations running proprietary versions of UNIX. Linux

	is also a full 32-bit operating system, utilizing the special protected-mode features

	of the Intel 80386, 80486, and Pentium processors.

	<P>

	<LI>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. For example, you can have multiple login sessions in

	different windows on the screen at one time. Other examples of X Window applications

	are <TT>xtetris</TT>, <TT>xvier</TT>, <TT>xlander</TT>, and <TT>x11perf</TT>.

	<P>

	<LI>Binary file support. The Linux kernel and loader works with ELF binaries, the

	latest standard in UNIX for relocatable binaries. Linux can also run native Java

	code, UNIX System VR4, and BSD binaries.

	<P>

	<LI>Java support. Linux kernels, when configured correctly, can also run Java applets

	as applications.

	<P>

	<LI>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 the phone lines with a modem.

	<P>

	<LI>Virtual memory. Linux can use a portion of your hard drive as virtual memory,

	expanding your total amount of available RAM.

	<P>

	<LI>ELF support and shared libraries. Linux also implements ELF binaries, as well

	as dynamic linking with older shared libraries, allowing programs that use standard

	subroutines to find the code for these subroutines in the libraries at runtime.

	<P>

	<LI>The Linux kernel uses no code from any other proprietary source. So you can actually

	look at it!

	<P>

	<LI>Linux supports (almost) all the features of commercial versions of UNIX. In fact,

	some of the features you find in Linux might not be available on other proprietary

	UNIX systems.

	<P>

	<LI>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, <TT>gawk</TT>,

	<TT>groff</TT>, and more. Many of the essential system utilities used by Linux are

	GNU software.

	<P>

	<LI>Linux is closely 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.

	<P>

	<LI>The Linux system runs exclusively in 32-bit mode. This is a major step up from

	a 16-bit integer limitation in MS-DOS and Windows 3.1x.

	<P>

	<LI>Linux has built-in support for networking, multitasking, and other features.

	You'll see this touted as &quot;New Technology&quot; in systems such as Windows NT.

	In fact, UNIX (and now, Linux) has implemented this &quot;New Technology&quot; for

	more than 15 years.

	<P>

	<LI>Linux is in a constant state of development. It's hard to keep up with the revisions

	that come up daily on the FTP sites on the Internet.

	<P>

	<LI>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 U.S. $30 to U.S. $200, you can save yourself some time and get

	CD-ROM or floppy-disk distributions from several commercial vendors. See Chapter

	2, &quot;Types of Linux.&quot;

</UL>



<P>In my opinion, the most important advantage of using Linux is that you get to

work with a real kernel. All 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.</P>

<P>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.



<DL>

	<DT></DT>

</DL>





<DL>

	<DD>

<HR>

<A NAME="Heading10<FONT COLOR="#000077"><B>NOTE: </B></FONT>Linux uses the

	386 chip protected-mode functions extensively and is a true 32-bit operating system.

	Linux simply does not run on an 8086, 8088, or 80286 computer.

<HR>



</DL>



<P>So, how reliable is Linux? Surprisingly, Linux is a very stable operating system.

I have used Linux on two commercial products and have found Linux to be a far more

cost-effective solution than a high-priced workstation. The only real bugs are with

alpha drivers (that's why they're alpha). For 99 percent of applications, however,

Linux is very robust.

<H3 ALIGN="CENTER"><A NAME="Heading11<FONT COLOR="#000077">The Downside of

Linux</FONT></H3>

<P>Linux is a hacker's kernel. This hacker attitude can be a daunting experience

for someone not familiar with UNIX.</P>

<P>As I stated earlier, the HOWTO documents in the LDP (in the <TT>docs</TT> directory

of the CD-ROM at the back of the book) have loads of tips and answers to frequently

asked questions (FAQ). If you are stuck, you can always look at the original files

on the CD-ROM. Of course, if booting your machine is a problem, you might have to

borrow some other computer to be able to read the CD-ROM.</P>

<P>So, live, human help is generally not available, nor is it a phone call away as

with a commercial version of UNIX. You can get help from the Internet newsgroups

and other members of the Linux community via e-mail. When it's midnight and your

system just won't boot like the <TT>README</TT> file said it would, however, you

do feel a sense of despair. So when using Linux, remember that it is truly a hacker's

operating system, developed by and for UNIX hackers.</P>

<P>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; Linux is

not guaranteed to work at all on your system. You are indeed on your own. Chances

are that the Linux version at the back of the book will work on your system, but

no one can guarantee this.</P>

<P>If you want a solid guarantee that Linux will work on your system, get a version

of Linux from a vendor who will explicitly spell out what systems they have tried

Linux on. Of course, this purchase of Linux might cost you a little money (anywhere

from U.S. $25 to about U.S. $100). The time spent in trying to debug your hardware

setup will be less, however, if you have someone guaranteeing a known setup. If the

no-name CD-ROM does not work on your system, you might be better off getting a CD-ROM

that does work (by looking at the documentation that comes with Linux or via a vendor).

Too often I get mail from readers of previous editions of this book telling about

their VGA card or CD-ROM not working, only to find that they do not even know the

model and name of the device.</P>

<P>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 that most UNIX

users never get to do, even after years of experience. Yes, you get to do it yourself,

but it isn't that easy. You might actually consider being nice to your local UNIX

system administrator after installing Linux for the first time.</P>

<P>Here are some other aspects of Linux you should be warned about:



<UL>

	<LI>Some of the features on your favorite UNIX system might not be available for

	your Linux system. Your choice in this matter is to write the application yourself,

	convince someone else to write it, or find an alternative process (the easiest way

	out, in most cases).

	<P>

	<LI>You do have to spend some time managing your Linux machine. It takes time and

	effort to manage your own Linux system.

</UL>



<P>You develop a knack for fixing problems from experience. Only with experience,

however, can you learn to recognize common problems and find or develop solutions.</P>

<P>Even with standard Linux distributions, sometimes little quirks need to be fixed

by hand for everything to work correctly. If you have previous UNIX experience, it

should be easy to find these problems. If you're new to UNIX, however, it would serve

you well to read up on using and running a UNIX system before you dive in.</P>

<P>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 read a good book on UNIX system administration, such as UNIX System V, Release

4 Administration, Second Edition (Sams Publishing, 1991).

<H3 ALIGN="CENTER"><A NAME="Heading12<FONT COLOR="#000077">About Linuxs Copyright</FONT></H3>

<P>Ah, yes, that old topic of copyrights. Compared to death and taxes, Linux copyrights

are a mere annoyance. Linux is not public domain software.</P>

<P>Actually, Linux is copyrighted under the GNU General Public License, sometimes

called the GPL or copyleft (instead of right). This copyleft license was developed

by the Free Software Foundation to allow programmers to write &quot;free software,&quot;

with &quot;free&quot; referring to freedom, not just cost. The GPL provides for the

protection of such free software in various ways:



<UL>

	<LI>It allows the original author to retain the software's copyright.

	<P>

	<LI>It allows others to take the software and modify it, or even base other programs

	on it.

	<P>

	<LI>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. In reselling

	or redistributing the software, however, you cannot restrict any of these rights

	from the party you're selling it to.

</UL>





<DL>

	<DT></DT>

</DL>





<DL>

	<DD>

<HR>

<A NAME="Heading13<FONT COLOR="#000077"><B>NOTE:</B> </FONT>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 so desire. You cannot hold back

	the source of your modifications.

<HR>



</DL>



<P>The original authors of the Linux software may never see a dime of these revenues.

This does not prevent authors from getting donations, though, nor does it prevent

anyone from charging a fee for the time and effort to make copies for distribution.

This is allowed by the GNU GPL because the point of free software isn't to make money.

The GNU GPL is simply an understanding between the authors of the software and those

who are using, distributing, or sel- ling it.</P>



<P>Another point is that all free software that is covered by the GNU GPL comes with

absolutely no warranty. But individual vendors, such as Red Hat, can provide support

for the software, which usually includes a warranty. Unless you explicitly purchase