Linux (pronounced with a short i, as in LIH-nucks) is a UNIX operating system clone which runs on a variety of platforms, especially personal computers with Intel 80386 or better processors. It supports a wide range of software, from TeX, to the X Window System, to the GNU C/C++ compiler, to TCP/IP. It's a versatile, bona fide implementation of UNIX, freely distributed under the terms of the GNU General Public License (see Appendix C). 

Linux can turn any 80386 or better personal computer into a workstation that puts the full power of UNIX at your fingertips. Businesses install Linux on entire networks of machines, and use the operating system to manage financial and hospital records, distributed computing environments, and telecommunications. Universities worldwide use Linux to teach courses on operating system programming and design. Computing enthusiasts everywhere use Linux at home for programming, productivity, and all-around hacking. 

What makes Linux so different is that it is a free implementation of UNIX. It was and still is developed cooperatively by a group of volunteers, primarily on the Internet, who exchange code, report bugs, and fix problems in an open-ended environment. Anyone is welcome to join the Linux development effort. All it takes is interest in hacking a free UNIX clone, and some programming know-how. 

A brief history of Linux

UNIX is one of the most popular operating systems worldwide because of its large support base and distribution. It was originally developed at AT&T as a multitasking system for minicomputers and mainframes in the 1970's, but has since grown to become one of the most widely-used operating systems anywhere, despite its sometimes confusing interface and lack of central standardization. 

Many hackers feel that UNIX is the Right Thing--the One True Operating System. Hence, the development of Linux by an expanding group of UNIX hackers who want to get their hands dirty with their own system. 

Versions of UNIX exist for many systems, from personal computers to supercomputers like the Cray Y-MP. Most versions of UNIX for personal computers are expensive and cumbersome. 

Linux is a free version of UNIX developed primarily by Linus Torvalds at the University of Helsinki in Finland, with the help of many UNIX programmers and wizards across the Internet. Anyone with enough know-how and gumption can develop and change the system. The Linux kernel uses no code from AT&T or any other proprietary source, and much of the software available for Linux was developed by the GNU project of the Free Software Foundation in Cambridge, Massachusetts, U.S.A.
However, programmers from all over the world have contributed to the growing pool of Linux software. 

Linux was originally developed as a hobby project by Linus Torvalds. It was inspired by Minix, a small UNIX system developed by Andy Tanenbaum. The first discussions about Linux were on the Usenet newsgroup, comp.os.minix. These discussions were concerned mostly with the development of a small, academic UNIX system for Minix users who wanted more. 

The very early development of Linux mostly dealt with the task-switching features of the 80386 protected-mode interface, all written in assembly code. Linus writes, 

After that it was plain sailing: hairy coding still, but I had some devices, and debugging was easier. I started using C at this stage, and it certainly speeds up development. This is also when I started to get serious about my megalomaniac ideas to make `a better Minix than Minix.' I was hoping I'd be able to recompile gcc under Linux someday...

Two months for basic setup, but then only slightly longer until I had a disk driver (seriously buggy, but it happened to work on my machine) and a small file system. That was about when I made 0.01 available (around late August of 1991): it wasn't pretty, it had no floppy driver, and it couldn't do much of anything. I don't think anybody ever compiled that version. But by then I was hooked, and didn't want to stop until I could chuck out Minix.''

No announcement was ever made for Linux version 0.01. The 0.01 sources weren't even executable. They contained only the bare rudiments of the kernel source and assumed that you had access to a Minix machine to compile and experiment with them. 

On October 5, 1991, Linus announced the first ``official'' version of Linux, which was version 0.02. At that point, Linus was able to run bash (the GNU Bourne Again Shell) and gcc (the GNU C compiler), but not much else. Again, this was intended as a hacker's system. The primary focus was kernel development--user support, documentation, and distribution had not yet been addressed. Today, the Linux community still seems to treat these issues as secondary to ``real programming''--kernel
development. 

As Linus wrote in comp.os.minix, 

Do you pine for the nice days of Minix-1.1, when men were men and wrote their own device drivers? Are you without a nice project and just dying to cut your teeth on an OS you can try to modify for your needs? Are you finding it frustrating when everything works on Minix? No more all-nighters to get a nifty program working? Then this post might be just for you.

As I mentioned a month ago, I'm working on a free version of a Minix-look-alike for AT-386 computers. It has finally reached the stage where it's even usable (though may not be, depending on what you want), and I am willing to put out the sources for wider distribution. It is just version 0.02...but I've successfully run bash, gcc, gnu-make, gnu-sed, compress, etc. under it.''

After version 0.03, Linus bumped up the version number to 0.10, as more people started to work on the system. After several further revisions, Linus increased the version number to 0.95 in March, 1992, to reflect his expectation that the system was ready for an ``official'' release soon. (Generally, software is not assigned the version number 1.0 until it is theoretically complete or bug-free.). Almost a year and a half later, in late December of 1993, the Linux kernel was still at version 0.99.pl14 -- asymptotically approaching 1.0. At the time of this writing, the current stable kernel version is 2.0 patchlevel 33, and version 2.1 is under development. 

Most of the major, free UNIX software packages have been ported to Linux, and commercial software is also available. More hardware is supported than in the original kernel versions. Many people have executed benchmarks on 80486 Linux systems and found them comparable with mid-range workstations from Sun Microsystems and Digital Equipment Corporation. Who would have ever guessed that this "little" UNIX clone would have grown up to take on the entire world of personal computing? 

System features

Linux supports features found in other implementations of UNIX, and many which aren't found elsewhere. 

Linux is a complete multitasking, multiuser operating system, as are all other versions of UNIX. This means that many users can log into and run programs on the same machine simultaneously. 

The Linux system is mostly compatible with several UNIX standards (inasmuch as UNIX has standards) at the source level, including IEEE POSIX.1, UNIX System V, and Berkely System Distribution UNIX. Linux was developed with source code portability in mind, and it's easy to find commonly used features that are shared by more than one platform. Much of the free UNIX software available on the Internet and elsewhere compiles under Linux ``right out of the box.'' In addition, all of the source code for the Linux system, including the kernel, device drivers, libraries, user programs, and development tools, is freely distributable. 

Other specific internal features of Linux include POSIX job control (used by shells like csh and bash), pseudoterminals ( pty devices), and support for dynamically loadable national or customized keyboard drivers. Linux supports virtual consoles that let you switch between login sessions on the same system console. Users of the screen program will find the Linux virtual console implementation familiar. 

The kernel can emulate 387-FPU instructions, and systems without a math coprocessor can run programs that require floating-point math capability. 

Linux supports various file systems for storing data, like the ext2 file system, which was developed specifically for Linux. The Xenix and UNIX System V file systems are also supported, as well as the Microsoft MS-DOS and Windows 95 VFAT file systems on a hard drive or floppy. The ISO 9660 CD-ROM file system is also supported. We'll talk more about file systems in chapters 2 and 4. 

Linux provides a complete implementation of TCP/IP networking software. This includes device drivers for many popular Token Ring and Ethernet cards, SLIP (Serial Line Internet Protocol) and PPP (Point-to-Point Protocol), which provide access to a TCP/IP network via a serial connection, PLIP (Parallel Line Internet Protocol), and NFS (Network File System). The complete range of TCP/IP clients and services is also supported, which includes FTP, telnet, NNTP, and SMTP. 

The Linux kernel is developed to use protected-mode features of Intel 80386 and better processors. In particular, Linux uses the protected-mode, descriptor based, memory-management paradigm, and other advanced features. Anyone familiar with 80386 protected-mode programming knows that this chip was designed for multitasking systems like UNIX. Linux exploits this functionality. 

The kernel supports demand-paged, loaded executables. Only those segments of a program which are actually in use are read into memory from disk. Also, copy-on-write pages are shared among executables. If several instances of a program are running at once, they share physical memory, which reduces overall usage. 

In order to increase the amount of available memory, Linux also implements disk paging. Up to one gigabyte of swap space may be allocated on disk (upt to 8 partitions of 128 megabytes each). When the system requires more physical memory, it swaps inactive pages to disk, letting you run larger applications and support more users. However, swapping data to disk is no substitute for physical RAM, which is much faster. 

The Linux kernel also implements a unified memory pool for user programs and disk cache. All free memory is used by the cache, which is reduced when running large programs. 

Executables use dynamically linked, shared libraries: code from a single library on disk. This is not unlike the SunOS shared library mechanism. Executable files occupy less disk space, especially those which use many library functions. There are also statically linked libraries for object debugging and maintaining ``complete'' binary files when shared libraries are not installed. The libraries are dynamically linked at run time, and the programmer can use his or her own routines in place of the standard library routines. 

To facilitate debugging, the kernel generates core dumps for post-mortem analysis. A core dump and an executable linked with debugging support allows a developer to determine what caused a program to crash. 

Software features

Virtually every utility one would expect of a standard UNIX implementation has been ported to Linux, including basic commands like ls, awk, tr, sed, bc, and more. The familiar working environment of other UNIX systems is duplicated on Linux. All standard commands and utilities are included. 

Many text editors are available, including vi, ex, pico, jove, and GNU emacs, and variants like Lucid emacs, which incorporates extensions of the X Window System, and joe. The text editor you're accustomed to using has more than likely been ported to Linux. 

The choice of a text editor is an interesting one. Many UNIX users prefer ``simple'' editors like vi. (The original author wrote this book with vi.) But vi has many limitations due to its age, and modern editors like emacs have gained popularity. emacs supports a complete, Lisp based macro language and interpreter, powerful command syntax, and other extensions. There are emacs macro packages which let you read electronic mail and news, edit directory contents, and even engage in artificially
intelligent psychotherapy sessions (indispensible for stressed-out Linux hackers). 

Most of the basic Linux utilities are GNU software. GNU utilities support advanced features that are not found in the standard versions of BSD and UNIX System Vprograms. For example, the GNU vi clone, elvis, includes a structured macro language that differs from the original implementation. However, GNU utilities are intended to remain compatible with their BSD and System V counterparts. Many people consider the GNU versions to be superior to the originals. 

A shell is a program which reads and executes commands from the user. In addition, many shells provide features like job control, managing several processes at once, input and output redirection, and a command language for writing shell scripts. A shell script is a program in the shell's command language and is analogous to a MS-DOS batch file. 

Many types of shells are available for Linux. The most important difference between shells is the command language. For example, the C SHell (csh) uses a command language similar to the C programming language. The classic Bourne SHell sh uses another command language. The choice of a shell is often based on the command language it provides, and determines, to a large extent, the qualities of your working environment under Linux. 

The GNU Bourne Again Shell (bash) is a variation of the Bourne Shell which includes many advanced features like job control, command history, command and filename completion, an emacs-like interface for editing command lines, and other powerful extensions to the standard Bourne Shell language. Another popular shell is tcsh, a version of the C Shell with advanced functionality similar to that found in bash. Other shells include zsh, a small Bourne-like shell; the Korn Shell (ksh); BSD's ash; and rc, the Plan 9 shell. 

If you're the only person using the system and refer to use vi and bash exclusively as your editor and shell, there's no reason to install other editors or shells. This ``do it yourself'' attitude is prevalent among Linux hackers and users. 

Text processing and word processing

Almost every computer user needs a method of preparing documents. In the world of personal computers, word processing is the norm: editing and manipulating text in a  What-You-See-Is-What-You-Get'' (WYSIWYG) environment and producing printed copies of the text, complete with graphics, tables, and ornamentation. 

Commercial word processors from Corel, Applix, and Star Division are available in the UNIX world, but text processing, which is quite different conceptually, is more common. In text processing systems, text is entered in a page-description language, which describes how the text should be formatted. Rather than enter text within a special word processing environment, you can modify text with any editor, like vi or emacs. Once you finish entering the source text (in the typesetting language), a separate program converts the source to a format suitable for printing. This is somewhat analogous to programming
in a language like C, and ``compiling'' the document into printable form. 

Many text processing systems are available for Linux. One is groff, the GNU version of the classic troff text formatter originally developed by Bell Labs and still used on many UNIX systems worldwide. Another modern text processing system is TeX, developed by Donald Knuth of computer science fame. Dialects of TeX, like LaTeX, are also available. 

Text processors like TeX and groff differ mostly in the syntax of their formatting languages. The choice of one formatting system over another is based upon what utilities are available to satisfy your needs, as well as personal taste. 

Many people consider groff's formatting language to be a bit obscure and use find TeX more readable. However, groff produces ASCII output which can be viewed on a terminal more easily, while TeX is intended primarily for output to a printing device. Various add-on programs are required to produce ASCII output from TeX formatted documents, or convert TeX input to groff format. 

Another program is texinfo, an extension to TeX which is used for software documentation developed by the Free Software Foundation. texinfo can produce printed output, or an online-browsable hypertext ``Info'' document from a single source file. Info files are the main format of documentation used in GNU software like emacs. 

Text processors are used widely in the computing community for producing papers, theses, magazine articles, and books. (This book is produced using LaTeX.) The ability to process source language as a text file opens the door to many extensions of the text processor itself. Because a source document is not stored in an obscure format that only one word processor can read, programmers can write parsers and translators for the formatting language, and thus extend the system. 

What does a formatting language look like? In general, a formatted source file consists mostly of the text itself, with control codes to produce effects like font and margin changes, and list formatting. 

Consider the following text: 

Mr. Torvalds:

We are very upset with your current plans to implement post-hypnotic suggestions in the Linux terminal driver code. We feel this way for three reasons:

1.Planting subliminal messages in the terminal driver is not only immoral, it is a waste of time;
2.It has been proven that ``post-hypnotic suggestions'' are ineffective when used upon unsuspecting UNIX hackers;
3.We have already implemented high-voltage electric shocks, as a security measure, in the code for login.

     We hope you will reconsider.

This text might appear in the LaTeX formatting language as the following:

\begin{quote}
Mr. Torvalds:

We are very upset with your current plans to implement {\em post-hypnotic suggestions\/} in the {\bf Linux} terminal driver code. We feel this way for three reasons:
\begin{enumerate}
\item Planting subliminal messages in the kernel driver is not only
      immoral, it is a waste of time;
\item It has been proven that ``post-hypnotic suggestions''
      are ineffective when used upon unsuspecting UNIX hackers;
\item We have already implemented high-voltage electric shocks, as
      a security measure, in the code for {\tt login}.
\end{enumerate}
We hope you will reconsider.
\end{quote}

The author enters the text using any text editor and generates formatted output by processing the source with LaTeX. At first glance, the typesetting language may appear to be obscure, but it's actually quite easy to understand. Using a text processing system enforces typographical standards when writing. All the enumerated lists within a document will look the same, unless the author modifies the definition of an enumerated list. The goal is to allow the author to concentrate on the text, not typesetting conventions. 

When writing with a text editor, one generally does not think about how the printed text will appear. The writer learns to visualize the finished text's appearance from the formatting commands in the source. 

WYSIWYG word processors are attractive for many reasons. They provide an easy-to-use visual interface for editing documents. But this interface is limited to aspects of text layout which are accessible to the user. For example, many word processors still provide a special format language for producing complicated expressions like mathematical formulae. This is text processing, albeit on a much smaller scale. 

A not-so-subtle benefit of text processing is that you specify exactly which format you need. In many cases, the text processing system requires a format specification. Text processing systems also allow source text to be edited with any text editor, instead of relying on format codes which are hidden beneath a word processor's opaque user interface. Further, the source text is easily converted to other formats. The tradeoff for this flexibility and power is the lack of WYSIWYG formatting. 

Some programs let you preview the formatted document on a graphics display device before printing. The xdvi program displays a ``device independent'' file generated by the TeX system under X. Applications like xfig and gimp provide WYSIWYG graphics interfaces for drawing figures and diagrams, which are subsequently converted to text processing language for inclusion in your document. 

Text processors like troff were around long before WYSIWYG word processing was available. Many people still prefer their versatility and independence from a graphics environment. 

Many text-processing-related utilities are available. The powerful METAFONT system, which is used to design fonts for TeX, is included in the Linux port of TeX. Other programs include ispell, an interactive spelling checker and corrector; makeindex, which generates indices in LaTeX documents; and many other groff and TeXbased macro packages which format many types of technical and mathematical texts. Conversion programs that translate between TeX or groff source to a myriad of other formats are also available. 

A newcomer to text formatting is YODL, written by Karel Kubat. YODL is an easy-to-learn language with filters to produce various output formats, like LaTeX, SGML, and HTML. 

Programming languages and utilities

Linux provides a complete UNIX programming environment which includes all of the standard libraries, programming tools, compilers, and debuggers which you would expect of other UNIX systems. 

Standards like POSIX.1 are supported, which allows software written for Linux to be easily ported to other systems. Professional UNIX programmers and system administrators use Linux to develop software at home, then transfer the software to UNIX systems at work. This not only saves a great deal of time and money, but also lets you work in the comfort of your own home. (One of the authors uses his system to develop and test X Window System applications at home, which can be directly compiled on workstations elsewhere.) Computer Science students learn UNIX programming and explore other aspects of the system, like kernel architecture. 

With Linux, you have access to the complete set of libraries and programming utilities and the complete kernel and library source code. 

Within the UNIX software world, systems and applications are often programmed in C or C++. The standard C and C++ compiler for Linux is GNU gcc, which is an advanced, modern compiler that supports C++, including AT&T 3.0 features, as well as Objective-C, another object-oriented dialect of C. 

Besides C and C++, other compiled and interpreted programming languages have been ported to Linux, like Smalltalk, FORTRAN, Java, Pascal, LISP, Scheme, and Ada (if you're masochistic enough to program in Ada, we aren't going to stop you). In addition, various assemblers for writing protected-mode 80386 code are available, as are UNIX hacking favorites like Perl (the script language to end all script languages) and Tcl/Tk (a shell-like command processing system which has support for
developing simple X Window System applications). 

The advanced gdb debugger can step through a program one line of source code at a time, or examine a core dump to find the cause of a crash. The gprof profiling utility provides performance statistics for your program, telling you where your program spends most of its execution time. As mentioned above, the emacs text editor provides interactive editing and compilation environments for various programming languages. Other tools include GNU make and imake, which manage compilation of
large applications, and RCS, a system for source code locking and revision control. 

Finally, Linux supports dynamically linked, shared libraries (DLLs), which result in much smaller binaries. The common subroutine code is linked at run-time. These DLLs let you override function definitions with your own code. For example, if you wish to write your own version of the malloc() library routine, the linker will use your new routine instead of the one in the libraries. 

The design and philosophy of Linux

New users often have a few misconceptions and false expectations about Linux. It is important to understand the philosophy and design of Linux in order to use it effectively. We'll start by describing how Linux is not designed. 

In commercial UNIX development houses, the entire system is developed under a rigorous quality assurance policy that utilizes source and revision control systems, documentation, and procedures to report and resolve bugs. Developers may not add features or change key sections of code on a whim. They must validate the change as a response to a bug report and subsequently ``check in'' all changes to the source control system, so that the changes may be reversed if necessary. Each developer is assigned one or more parts of the system code, and only that developer can alter those sections of the code while it is ``checked out'' (that is, while the code is under his or her control). 

Organizationally, a quality assurance department runs rigorous tests on each new version of the operating system and reports any bugs. The developers fix these bugs as reported. A complex system of statistical analysis is used to ensure that a certain percentage of bugs are fixed before the next release, and that the operating system as a whole passes certain release criteria. 

The software company, quite reasonably, must have quantitative proof that the next revision of the operating system is ready to be shipped; hence, the gathering and analysis of statistics about the performance of the operating system. It is a big job to develop a commercial UNIX system, often large enough to employ hundreds, if not thousands, of programmers, testers, documenters, and administrative personnel. Of course, no two commercial UNIX vendors are alike, but that is the general picture. 

The Linux model of software development discards the entire concept of organized development, source code control systems, structured bug reporting, and statistical quality control. Linux is, and likely always will be, a hacker's operating system. (By hacker, I mean a feverishly dedicated programmer who enjoys exploiting computers and does interesting things with them. This is the original definition of the term, in contrast to the connotation of hacker as a computer wrongdoer, or outlaw.) 

There is no single organization responsible for developing Linux. Anyone with enough know-how has the opportunity to help develop and debug the kernel, port new software, write documentation, and help new users. For the most part, the Linux community communicates via mailing lists and Usenet newsgroups. Several conventions have sprung up around the development effort. Anyone who wishes to have their code included in the ``official'' kernel, mails it to Linus Torvalds. He will test and include the code in the kernel as long as it doesn't break things or go against the overall design of the system. 

The system itself is designed using an open-ended, feature-minded approach. The number of new features and critical changes to the system has recently diminished, and the general rule is that a new version of the kernel will be released every few weeks. Of course, this is a rough figure. New release criteria include the number of bugs to be fixed, feedback from users testing pre-release versions of the code, and the amount of sleep Linus Torvalds has had this week. 

Suffice it to say that not every bug is fixed, nor is every problem ironed out between releases. As long as the revision appears to be free of critical or recurring bugs, it is considered to be stable, and the new version is released. The thrust behind Linux development is not to release perfect, bug-free code: it is to develop a free UNIX implementation. Linux is for the developers, more than anyone else. 

Anyone who has a new feature or software application generally makes it available in an alpha version--that is, a test version, for those brave users who want to hash out problems in the initial code. Because the Linux community is largely based on the Internet, alpha software is usually uploaded to one or more Linux FTP sites (see Appendix B), and a message is posted to one of the Linux Usenet newsgroups about how to obtain and test the code. Users who download and test alpha software can then mail results, bug fixes, and questions to the author. 

After the initial bugs have been fixed, the code enters a beta test stage, in which it is usually considered stable but not complete. It works, but not all of the features may be present. The software may also go directly to a final stage, in which the software is considered complete and usable. 

Keep in mind that these are only conventions--not rules. Some developers may feel so confident of their software that they decide it isn't necessary to release alpha or test versions. It is always up to the developer to make these decisions. 

You might be amazed at how such an unstructured system of volunteers who program and debug a complete UNIX system gets anything done at all. As it turns out, this is one of the most efficient and motivated development efforts ever employed. The entire Linux kernel is written from scratch, without code from proprietary sources. It takes a huge amount of work to port all the free software under the sun to Linux. Libraries are written and ported, file systems are developed, and hardware drivers are
written for many popular devices--all due to the work of volunteers. 

Linux software is generally released as a distribution, a set of prepackaged software which comprises an entire system. It would be difficult for most users to build a complete system from the ground up, starting with the kernel, adding utilities, and installing all of the necessary software by hand. Instead, many software distributions are available which include everything necessary to install and run a complete system. There is no single, standard distribution--there are many, and each has its own advantages and disadvantages. 

Differences between Linux and other operating systems

It is important to understand the differences between Linux and other operating systems, like MS-DOS, OS/2, and the other implementations of UNIX for personal computers. First of all, Linux coexists happily with other operating systems on the same machine: you can run MS-DOS and OS/2 along with Linux on the same system without problems. There are even ways to interact between various operating systems, as we'll see. 

Why use Linux?

Why use Linux, instead of a well known, well tested, and well documented commercial operating system? We could give you a thousand reasons. One of the most important, however, is that Linux is an excellent choice for personal UNIX computing. If you're a UNIX software developer, why use MS-DOS at home? Linux allows you to develop and test UNIX software on your PC, including database and X Window System applications. If you're a student, chances are that your university computing systems run UNIX. You can run your own UNIX system and tailor it to your needs. Installing and running Linux is also an excellent way to learn UNIX if you don't have access to other UNIX machines. 

But let's not lose sight. Linux isn't only for personal UNIX users. It is robust and complete enough to handle large tasks, as well as distributed computing needs. Many businesses--especially small nes--have moved their systems to Linux in lieu of other UNIX based, workstation environments. Universities have found that Linux is perfect for teaching courses in operating systems design. Large, commercial software vendors have started to realize the opportunities which a free operating system can provide. 

Linux vs. MS-DOS

It's not uncommon to run both Linux and MS-DOS on the same system. Many Linux users rely on MS-DOS for applications like word processing. Linux provides its own analogs for these applications, but you might have a good reason to run MS-DOS as well as Linux. If your dissertation is written using WordPerfect for MS-DOS, you may not be able to convert it easily to TeX or some other format. Many commercial applications for MS-DOS aren't available for Linux yet, but there's no reason that you can't use both. 

MS-DOS does not fully utilize the functionality of 80386 and 80486 processors. On the other hand, Linux runs completely in the processor's protected mode, and utilizes all of its features. You can directly access all of your available memory (and beyond, with virtual RAM). Linux provides a complete UNIX interface which is not available under MS-DOS. You can easily develop and port UNIX applications to Linux, but under MS-DOS you are limited to a subset of UNIX functionality. 

Linux and MS-DOS are different entities. MS-DOS is inexpensive compared to other commercial operating systems and has a strong foothold in the personal computer world. No other operating system for the personal computer has reached the level of popularity of MS-DOS, because justifying spending $1,000 for other operating systems alone is unrealistic for many users. Linux, however, is free, and you may finally have the chance to decide for yourself. 

You can judge Linux vs. MS-DOS based on your expectations and needs. Linux is not for everybody. If you always wanted to run a complete UNIX system at home, without the high cost of other UNIX implementations for personal computers, Linux may be what you're looking for. 

Linux vs. The Other Guys

A number of other advanced operating systems have become popular in the PC world. Specifically, IBM's OS/2 and Microsoft Windows have become popular for users upgrading from MS-DOS. 

Both OS/2 and Windows NT are full featured multitasking operating systems, like Linux. OS/2, Windows NT, and Linux support roughly the same user interface, networking, and security features. However, the real difference between Linux and The Other Guys is the fact that Linux is a version of UNIX, and benefits from contributions of the UNIX community at large. 

What makes UNIX so important? Not only is it the most popular operating system for multiuser machines, it is a foundation of the free software world. Much of the free software available on the Internet is written specifically for UNIX systems. 

There are many implementations of UNIX from many vendors. No single organization is responsible for its distribution. There is a large push in the UNIX community for standardization in the form of open systems, but no single group controls this design. Any vendor (or, as it turns out, any hacker) may develop a standard implementation of UNIX. 

OS/2 and Microsoft operating systems, on the other hand, are proprietary. The interface and design are controlled by a single corporation, which develops the operating system code. In one sense, this kind of organization is beneficial because it sets strict standards for programming and user interface design, unlike those found even in the open systems community. 

Several organizations have attempted the difficult task of standardizing the UNIX programming interface. Linux, in particular, is mostly compliant with the POSIX.1 standard. As time goes by, it is expected that the Linux system will adhere to other standards, but standardization is not the primary goal of Linux development. 

Linux vs. other implementations of UNIX

Several other implementations of UNIX exist for 80386 or better personal computers. The 80386 architecture lends itself to UNIX, and vendors have taken advantage of this. 

Oher implementations of UNIX for the personal computer are similar to Linux. Almost all commercial versions of UNIX support roughly the same software, programming environment, and networking features. However, there are differences between Linux and commercial versions of UNIX. 

Linux supports a different range of hardware than commercial implementations. In general, Linux supports most well-known hardware devices, but support is still limited to hardware which the developers own. Commercial UNIX vendors tend to support more hardware at the outset, but the list of hardware devices which Linux supports is expanding continuously. 

Many users report that Linux is at least as stable as commercial UNIX systems. Linux is still under development, but the two-pronged release philosophy has made stable versions available without impeding development. 

The most important factor for many users is price. Linux software is free if you can download it from the Internet or another computer network. If you do not have Internet access, you can still purchase Linux inexpensively via mail order on diskette, tape, or CD-ROM. 

Of course, you may copy Linux from a friend who already has the software, or share the purchase cost with someone else. If you plan to install Linux on a large number of machines, you need only purchase a single copy of the software--Linux is not distributed with a ``single machine'' license. 

The value of commercial UNIX implementations should not be demeaned. In addition to the price of the software itself, one often pays for documentation, support, and quality assurance. These are very important factors for large institutions, but personal computer users may not require these benefits. In any case, many businesses and universities have found that running Linux in a lab of inexpensive personal computers is preferable to running a commercial version of UNIX in a lab of workstations. Linux can provide workstation functionality on a personal computer at a fraction of the cost. 

Linux systems have travelled the high seas of the North Pacific, and manage telecommunications and data analysis for an oceanographic research vessel. Linux systems are used at research stations in Antarctica. Several hospitals maintain patient records on Linux systems. 

Other free or inexpensive implementations of UNIX are available for the 80386 and 80486. One of the best known is 386BSD, an implementation of BSD UNIX for the 80386. The 386BSD package is comparable to Linux in many ways, but which one is better depends on your needs and expectations. The only strong distinction we can make is that Linux is developed openly, and any volunteer can aid in the development process, while 386BSD is developed by a closed team of programmers.
Because of this, serious philosophical and design differences exist between the two projects. The goal of Linux is to develop a complete UNIX system from scratch (and have a lot of fun in the process), and the goal of 386BSD is in part to modify the existing BSD code for use on the 80386. 

NetBSD is another port of the BSD NET/2 distribution to several machines, including the 80386. NetBSD has a slightly more open development structure, and is comparable to 386BSD in many respects. 

Another project of note is HURD, an effort by the Free Software Foundation to develop and distribute a free version of UNIX for many platforms. Contact the Free Software Foundation (the address is given in Appendix C) for more information about this project. At the time of this writing, HURD is still under development. 

Other inexpensive versions of UNIX exist as well, like Minix, an academic but useful UNIX clone upon which early development of Linux was based. Some of these implementations are mostly of academic interest, while others are full fledged systems.