rhl01.htm

linux的初学电子书

<LI>The Linux kernel uses no code from AT&amp;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.

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<LI>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.

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<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, gawk, groff, and so on. Many of the essential system utilities used by Linux are GNU software.

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<LI>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.

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<LI>Virtual memory support. Linux utilizes all of your system's memory, without memory limits or segmentation through the use of a virtual memory manager.

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<LI>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.

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<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 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).

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<P>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.

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<P>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.

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<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.</NOTE>

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<FONT SIZE=5 COLOR="#FF0000"><B>The Downside of Linux and the Reason for This Book</B></FONT></CENTER></H3>

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<P>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.

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<P>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.

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<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, whereas Linux is not guaranteed to work at all on your system. You are indeed on your own.

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<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 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.

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

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<LI>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).

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<LI>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.

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<LI>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.

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<P>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.

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<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 find a good book on using UNIX system administration.

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<FONT SIZE=5 COLOR="#FF0000"><B>About Linux's Copyright</B></FONT></CENTER></H3>

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<P>Ah, yes&#151;that old topic of copyrights. Compared to death and taxes, Linux copyrights are a mere annoyance.

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<P>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 &quot;free 
software,&quot; where &quot;free&quot; refers to freedom, not just cost. The GPL provides for the protection of such free software in a number of ways:

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

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

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<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. However, in reselling or redistributing the software, you cannot restrict any of these rights from the 
party you're selling it to.

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<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.</NOTE>

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<P>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.

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<P>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.

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<P>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 <A HREF="rhlxe.htm" tppabs="http://202.113.16.101/%7eeb%7e/Red%20Hat%20Linux%20Unleashed/rhlxe.htm">Appendix E</A>, &quot;Copyright 
Information.&quot; 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.

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<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.</NOTE>

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<FONT SIZE=5 COLOR="#FF0000"><B>Hardware Requirements</B></FONT></CENTER></H3>

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<P>Now that you know a little about the good and bad points of Linux, let's see what's required in terms of hardware.

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<P>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.

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<P>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.

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<P>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.

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<P>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.

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<P>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.

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<P>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:

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<NOTE>If you're in the market for a new system, you should heed the following recommendations.</NOTE>

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<LI>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.

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<LI>  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.

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