# What is Linux?

We will start with an overview of how Linux became the operating system it is today. We will discuss past and future development and take a closer look at the advantages and disadvantages of this system. We will talk about distributions, about Open Source in general and try to explain a little something about GNU.

This chapter answers questions like:

- What is Linux?

- Where and how did Linux start?

- Isn't Linux that system where everything is done in text mode?

- Does Linux have a future or is it just hype?

- What are the advantages of using Linux?

- What are the disadvantages?

- What kinds of Linux are there and how do I choose the one that fits me?

- What are the Open Source and GNU movements?

## History

### UNIX

In order to understand the popularity of Linux, we need to travel back in time, about 30 years ago...

Imagine computers
as big as houses, even stadiums. While the sizes of those computers posed substantial problems, there was one thing that made this even worse: every computer had a different operating system. Software was always customized to serve a specific purpose, and software for one given system didn't run on another system. Being able to work with one system didn't automatically mean that you could work with another. It was difficult, both for the users and the system administrators.

Computers were extremely expensive then, and sacrifices had to be made even after the original purchase just to get the users to understand how they worked. The total cost per unit of computing power was enormous.

Technologically the world was not quite that advanced, so they had to live with the size for another decade. In 1969, a team of developers in the Bell Labs laboratories started working on a solution for the software problem, to address these compatibility issues. They developed a new operating
system, which was

1. Simple and elegant.

2. Written in the C programming language instead of in assembly code.

3. Able to recycle code.

The Bell Labs developers named their project UNIX.

The code recycling features were very important. Until then, all commercially available computer systems were written in a code specifically developed for one system. UNIX on the other hand needed only a small piece of that special code, which is now commonly named the kernel. This kernel is the only piece of code that needs to be adapted for every specific system and forms the base of the UNIX system. The operating system and all other functions were built around this kernel and written in a higher programming language, C. This language was especially developed for creating the UNIX system. Using this new technique, it was much easier to develop an operating system that could run on many different types of hardware.

The software vendors were quick to adapt, since they could sell ten times more software almost effortlessly. Weird new situations came in existence: imagine for instance computers from different vendors communicating in the same network, or users working on different systems without the need for extra education to use another computer. UNIX did a great deal to help users become compatible with different systems.

Throughout the next couple of decades the development of UNIX continued. More things became possible to do and more hardware and software vendors added support for UNIX to their products.

UNIX was initially found only in very large environments with mainframes and minicomputers (note that a PC is a micro computer). You had to work at a university, for the government or for large financial corporations in order to get your hands on a UNIX system.

But smaller computers were being developed, and by the end of the 80's, many people had home computers. By that time, there were several versions of UNIX available for the PC architecture, but none of them were truly free and more important: they were all terribly slow, so most people ran MS DOS or Windows 3.1 on their home PCs.

### Linus and Linux

By the beginning of the 90s home PCs were finally powerful enough to run a full blown UNIX. Linus
Torvalds, a young man studying computer science at the university of Helsinki, thought it would be a good idea to have some sort of freely available academic version of UNIX, and promptly started to code.

He started to ask questions, looking for answers and solutions that would help him get UNIX on his PC. Below is one of his first posts in comp.os.minix, dating from 1991:

    From: torvalds@klaava.Helsinki.FI (Linus Benedict Torvalds)
    Newsgroups: comp.os.minix
    Subject: Gcc-1.40 and a posix-question
    Message-ID: <1991Jul3.100050.9886@klaava.Helsinki.FI>
    Date: 3 Jul 91 10:00:50 GMT
    Hello netlanders,
    Due to a project I'm working on (in minix), I'm interested in the posix
    standard definition. Could somebody please point me to a (preferably)
    machine-readable format of the latest posix rules? Ftp-sites would be
    nice.

From the start, it was Linus' goal to have a free system
that was completely compliant with the original UNIX. That is why he asked for POSIX standards, POSIX still being the standard for UNIX.

In those days plug-and-play wasn't invented yet, but so many people were interested in having a UNIX system of their own, that this was only a small obstacle. New drivers became available for all kinds of new hardware, at a continuously rising speed. Almost as soon as a new piece of hardware became available, someone bought it and submitted it to the Linux test, as the system was gradually being called, releasing more free code for an ever wider range of hardware. These coders didn't stop at their PC's; every piece of hardware they could find was useful for Linux.

Back then, those people were called nerds or freaks, but it didn't matter to them, as long as the supported hardware list grew longer and longer. Thanks to these people, Linux is now not only ideal to run on new PC's, but is also the system of choice for old and exotic hardware that would be useless if Linux didn't exist.

Two years after Linus' post, there were 12000 Linux users. The project, popular with hobbyists, grew steadily, all the while staying within the bounds of the POSIX standard. All the features of UNIX were added over the next couple of years, resulting in the mature operating system Linux has become today. Linux is a full UNIX clone, fit for use on workstations as well as on middle-range and high-end servers. Today, a lot of the important players on the hard- and software market each have their team of Linux developers; at your local dealer's you can even buy pre-installed Linux systems with official support - eventhough there is still a lot of hard- and software that is not supported, too.

### Current application of Linux systems

Today Linux
has joined the desktop market. Linux developers concentrated on networking and services in the beginning, and office applications have been the last barrier to be taken down. We don't like to admit that Microsoft is ruling this market, so plenty of alternatives have been started over the last couple of years to make Linux an acceptable choice as a workstation, providing an easy user interface and MS compatible office applications like word processors, spreadsheets, presentations and the like.

On the server side, Linux is well-known as a stable and reliable platform, providing database and trading services for companies like Amazon, the well-known online bookshop, US Post Office, the German army and many others. Especially Internet providers and Internet service providers have grown fond of Linux as firewall, proxy- and web server, and you will find a Linux box within reach of every UNIX system administrator who appreciates a comfortable management station. Clusters of Linux machines are used in the creation of movies such as Titanic, Shrek and others. In post offices, they are the nerve centers that route mail and in large search engine, clusters are used to perform internet searches.These are only a few of the thousands of heavy-duty jobs that Linux is performing day-to-day across the world.

It is also worth to note that modern Linux not only runs on workstations, mid- and high-end servers, but also on gadgets like PDA's, mobiles, a shipload of embedded applications and even on experimental wristwatches. This makes Linux the only operating system in the world covering such a wide range of hardware.

## The user interface

### Is Linux difficult?

Whether Linux is difficult
to learn depends on the person you're asking. Experienced UNIX users will say no, because Linux is an ideal operating system for power-users and programmers, because it has been and is being developed by such people.

Everything a good programmer can wish for is available: compilers, libraries, development and debugging tools. These packages come with every standard Linux distribution. The C-compiler is included for free - as opposed to many UNIX distributions demanding licensing fees for this tool. All the documentation and manuals are there, and examples are often included to help you get started in no time. It feels like UNIX and switching between UNIX and Linux is a natural thing.

In the early days of Linux, being an expert was kind of required to start using the system. Those who mastered Linux felt better than the rest of the lusers who hadn't seen the light yet. It was common practice to tell a beginning user to RTFM (read the manuals). While the manuals were on every system, it was difficult to find the documentation, and even if someone did, explanations were in such technical terms that the new user became easily discouraged from learning the system.

The Linux-using community started to realize that if Linux was ever to be an important player on the operating system market, there had to be some serious changes in the accessibility of the system.

### Linux for non-experienced users

Companies such as RedHat, SuSE and Mandriva have sprung up, providing packaged Linux distributions suitable for mass consumption. They integrated a great deal of graphical user interfaces
(GUIs
), developed by the community, in order to ease management of programs and services. As a Linux user today you have all the means of getting to know your system inside out, but it is no longer necessary to have that knowledge in order to make the system comply to your requests.

Nowadays you can log in graphically and start all required applications without even having to type a single character, while you still have the ability to access the core of the system if needed. Because of its structure, Linux allows a user to grow into the system: it equally fits new and experienced users. New users are not forced to do difficult things, while experienced users are not forced to work in the same way they did when they first started learning Linux.

While development in the service area continues, great things are being done for desktop
users, generally considered as the group least likely to know how a system works. Developers of desktop applications are making incredible efforts to make the most beautiful desktops you've ever seen, or to make your Linux machine look just like your former MS Windows or an Apple workstation. The latest developments also include 3D acceleration support and support for USB devices, single-click updates of system and packages, and so on. Linux has these, and tries to present all available services in a logical form that ordinary people can understand. Below is a short list containing some great examples; these sites have a lot of screenshots that will give you a glimpse of what Linux on the desktop
can be like:

## Does Linux have a future?

### Open Source

The idea behind Open Source
software is rather simple: when programmers can read, distribute and change code, the code will mature. People can adapt it, fix it, debug it, and they can do it at a speed that dwarfs the performance of software developers at conventional companies. This software will be more flexible and of a better quality than software that has been developed using the conventional channels, because more people have tested it in more different conditions than the closed software developer ever can.

The Open Source
initiative started to make this clear to the commercial world, and very slowly, commercial vendors are starting to see the point. While lots of academics and technical people have already been convinced for 20 years now that this is the way to go, commercial vendors needed applications like the Internet to make them realize they can profit from Open Source. Now Linux has grown past the stage where it was almost exclusively an academic system, useful only to a handful of people with a technical background. Now Linux provides more than the operating system: there is an entire infrastructure supporting the chain of effort of creating an operating system, of making and testing programs for it, of bringing everything to the users, of supplying maintenance, updates and support and customizations, etcetera. Today, Linux is ready to accept the challenge of a fast-changing world.

### Ten years of experience at your service

While Linux is probably the most well-known Open Source initiative, there is another project that contributed enormously to the popularity of the Linux operating system. This project is called SAMBA
, and its achievement is the reverse engineering of the Server Message Block (SMB)/Common Internet File System (CIFS) protocol used for file- and print-serving on PC-related machines, natively supported by MS Windows NT and OS/2, and Linux. Packages are now available for almost every system and provide interconnection solutions in mixed environments using MS Windows protocols: Windows-compatible (up to and includingWinXP) file- and print-servers.

Maybe even more successful than the SAMBA project is the Apache HTTP server project. The server runs on UNIX, Windows NT and many other operating systems. Originally known as A PAtCHy server, based on existing code and a series of patch files, the name for the matured code deserves to be connoted with the native American tribe of the Apache, well-known for their superior skills in warfare strategy and inexhaustible endurance. Apache has been shown to be substantially faster, more stable and more feature-full than many other web servers. Apache is run on sites that get millions of visitors per day, and while no official support is provided by the developers, the Apache user community provides answers to all your questions. Commercial support is now being provided by a number of third parties.

In the category of office applications, a choice of MS Office
suite clones is available, ranging from partial to full implementations of the applications available on MS Windows workstations. These initiatives helped a great deal to make Linux acceptable for the desktop market, because the users don't need extra training to learn how to work with new systems. With the desktop comes the praise of the common users, and not only their praise, but also their specific requirements, which are growing more intricate and demanding by the day.

The Open Source
community, consisting largely of people who have been contributing for over half a decade, assures Linux' position as an important player on the desktop market as well as in general IT application. Paid employees and volunteers alike are working diligently so that Linux can maintain a position in the market. The more users, the more questions. The Open Source community makes sure answers keep coming, and watches the quality of the answers with a suspicious eye, resulting in ever more stability and accessibility.

Listing all the available Linux software is beyond the scope of this guide, as there are tens of thousands of packages. Throughout this course we will present you with the most common packages, which are almost all freely available. In order to take away some of the fear of the beginning user, here's a screenshot of one of your most-wanted programs. You can see for yourself that no effort has been spared to make users who are switching from Windows feel at home:

#### OpenOffice MS-compatible Spreadsheet

OpenOffice spreadsheet looks just like MS Office .xls file.

## Properties of Linux

### Linux Pros

A lot of the advantages
of Linux are a consequence of Linux' origins, deeply rooted in UNIX, except for the first advantage
, of course:

- Linux is free:

  As in free beer
  , they say. If you want to spend absolutely nothing, you don't even have to pay the price of a CD. Linux can be downloaded in its entirety from the Internet completely for free. No registration fees, no costs per user, free updates, and freely available source code in case you want to change the behavior of your system.

  Most of all, Linux is free as in free speech:

  The license commonly used is the GNU Public License
  (GPL
  ). The license says that anybody who may want to do so, has the right to change Linux and eventually to redistribute a changed version, on the one condition that the code is still available after redistribution. In practice, you are free to grab a kernel image, for instance to add support for teletransportation machines or time travel and sell your new code, as long as your customers can still have a copy of that code.

- Linux is portable to any hardware platform:

  A vendor who wants to sell a new type of computer and who doesn't know what kind of OS his new machine will run (say the CPU in your car or washing machine), can take a Linux kernel and make it work
  on his hardware, because documentation related to this activity is freely available.

- Linux was made to keep on running:

  As with UNIX
  , a Linux system expects to run without rebooting all the time. That is why a lot of tasks are being executed at night or scheduled automatically for other calm moments, resulting in higher availability during busier periods and a more balanced use of the hardware. This property allows for Linux to be applicable also in environments where people don't have the time or the possibility to control their systems night and day.

- Linux is secure and versatile:

  The security model used in Linux
  is based on the UNIX idea of security, which is known to be robust and of proven quality. But Linux is not only fit for use as a fort against enemy attacks from the Internet: it will adapt equally to other situations, utilizing the same high standards for security. Your development machine or control station will be as secure as your firewall.

- Linux is scalable:

  From a Palmtop with 2 MB of memory to a petabyte storage cluster with hundreds of nodes
  : add or remove the appropriate packages and Linux fits all. You don't need a supercomputer anymore, because you can use Linux to do big things using the building blocks provided with the system. If you want to do little things, such as making an operating system for an embedded processor or just recycling your old 486, Linux will do that as well.

- The Linux OS and most Linux applications have very short debug-times:

  Because Linux
  has been developed and tested by thousands of people, both errors and people to fix them are usually found rather quickly. It sometimes happens that there are only a couple of hours between discovery and fixing of a bug.

### Linux Cons

- There are far too many different
  distributions:

  Quot capites, tot rationes, as the Romans already said: the more people, the more opinions. At first glance, the amount of Linux distributions can be frightening, or ridiculous, depending on your point of view. But it also means that everyone will find what he or she needs. You don't need to be an expert to find a suitable release.

  When asked, generally every Linux user will say that the best distribution is the specific version he is using. So which one should you choose? Don't worry too much about that: all releases contain more or less the same set of basic packages. On top of the basics, special third party software is added making, for example, TurboLinux more suitable for the small and medium enterprise, RedHat for servers and SuSE for workstations. However, the differences are likely to be very superficial. The best strategy is to test a couple of distributions; unfortunately not everybody has the time for this. Luckily, there is plenty of advice on the subject of choosing your Linux. A quick search on Google, using the keywords choosing your distribution brings up tens of links to good advise. The Installation HOWTO also discusses choosing your distribution.

- Linux is not very user friendly and confusing for beginners:

  It must be said that Linux, at least the core system, is less userfriendly to use than MS Windows and certainly more difficult than MacOS, but... In light of its popularity, considerable effort has been made to make Linux even easier to use, especially for new users. More information is being released daily, such as this guide, to help fill the gap for documentation available to users at all levels.

- Is an Open Source product trustworthy?

  How can something that is free also be reliable
  ? Linux users have the choice whether to use Linux or not, which gives them an enormous advantage compared to users of proprietary software, who don't have that kind of freedom. After long periods of testing, most Linux users come to the conclusion that Linux is not only as good, but in many cases better and faster that the traditional solutions. If Linux were not trustworthy, it would have been long gone, never knowing the popularity it has now, with millions of users. Now users can influence their systems and share their remarks with the community, so the system gets better and better every day. It is a project that is never finished, that is true, but in an ever changing environment, Linux is also a project that continues to strive for perfection.

## Linux Flavors

### Linux and GNU

Although there are a large number of Linux implementations, you will find a lot of similarities in the different distributions, if only because every Linux machine is a box with building blocks that you may put together following your own needs and views. Installing the system is only the beginning of a longterm relationship. Just when you think you have a nice running system, Linux will stimulate your imagination and creativeness, and the more you realize what power the system can give you, the more you will try to redefine its limits.

Linux may appear different depending on the distribution
, your hardware and personal taste, but the fundamentals on which all graphical and other interfaces are built, remain the same. The Linux system is based on GNU
tools (Gnu's Not UNIX
), which provide a set of standard ways to handle and use the system. All GNU tools are open source, so they can be installed on any system. Most distributions offer pre-compiled packages of most common tools, such as RPM packages on RedHat and Debian packages (also called deb or dpkg) on Debian, so you needn't be a programmer to install a package on your system. However, if you are and like doing things yourself, you will enjoy Linux all the better, since most distributions come with a complete set of development tools, allowing installation of new software purely from source code. This setup also allows you to install software even if it does not exist in a pre-packaged form suitable for your system.

A list of common GNU
software:

- Bash: The GNU shell

- GCC: The GNU C Compiler

- GDB: The GNU Debugger

- Coreutils: a set of basic UNIX-style utilities, such as `ls`, `cat` and `chmod`

- Findutils: to search and find files

- Fontutils: to convert fonts from one format to another or make new fonts

- The Gimp: GNU Image Manipulation Program

- Gnome: the GNU desktop environment

- Emacs: a very powerful editor

- Ghostscript and Ghostview: interpreter and graphical frontend for PostScript files.

- GNU Photo: software for interaction with digital cameras

- Octave: a programming language, primarily intended to perform numerical computations and image processing.

- GNU SQL: relational database system

- Radius: a remote authentication and accounting server

- ...

Many commercial applications are available for Linux, and for more information about these packages we refer to their specific documentation. Throughout this guide we will only discuss freely available software, which comes (in most cases) with a GNU license.

To install missing
or new packages, you will need some form of software management. The most common implementations include RPM and dpkg. RPM is the RedHat Package Manager, which is used on a variety of Linux systems, eventhough the name does not suggest this. Dpkg is the Debian package management system, which uses an interface called `apt-get`, that can manage RPM packages as well. Novell Ximian Red Carpet is a third party implementation of RPM with a graphical front-end. Other third party software vendors may have their own installation procedures, sometimes resembling the InstallShield and such, as known on MS Windows and other platforms. As you advance into Linux, you will likely get in touch with one or more of these programs.

### GNU/Linux

The Linux kernel (the bones of your system, see ) is not part of the GNU
project but uses the same license as GNU software. A great majority of utilities and development tools (the meat of your system), which are not Linux-specific, are taken from the GNU project. Because any usable system must contain both the kernel and at least a minimal set of utilities, some people argue that such a system should be called a GNU/Linux system.

In order to obtain the highest possible degree of independence between distributions, this is the sort of Linux that we will discuss throughout this course. If we are not talking about a GNU/Linux system, the specific distribution, version or program name will be mentioned.

### Which distribution should I install?

Prior to installation
, the most important factor is your hardware. Since every Linux distribution contains the basic packages and can be built to meet almost any requirement (because they all use the Linux kernel), you only need to consider if the distribution will run on your hardware. LinuxPPC for example has been made to run on Apple and other PowerPCs and does not run on an ordinary x86 based PC. LinuxPPC does run on the new Macs, but you can't use it for some of the older ones with ancient bus technology. Another tricky case is Sun hardware, which could be an old SPARC CPU or a newer UltraSparc, both requiring different versions of Linux.

Some Linux distributions are optimized for certain processors, such as Athlon CPUs, while they will at the same time run decent enough on the standard 486, 586 and 686 Intel processors. Sometimes distributions for special CPUs are not as reliable, since they are tested by fewer people.

Most Linux distributions offer a set of programs for generic PCs with special packages containing optimized kernels for the x86 Intel based CPUs. These distributions are well-tested and maintained on a regular basis, focusing on reliant server implementation and easy installation and update procedures. Examples are Debian, Ubuntu, Fedora, SuSE and Mandriva, which are by far the most popular Linux systems and generally considered easy to handle for the beginning user, while not blocking professionals from getting the most out of their Linux machines. Linux also runs decently on laptops and middle-range servers. Drivers for new hardware are included only after extensive testing, which adds to the stability of a system.

While the standard desktop might be Gnome
on one system, another might offer KDE by default. Generally, both Gnome and KDE are available for all major Linux distributions. Other window and desktop managers are available for more advanced users.

The standard installation process allows users to choose between different basic setups, such as a workstation, where all packages needed for everyday use and development are installed, or a server installation, where different network services can be selected. Expert users can install every combination of packages they want during the initial installation process.

The goal of this guide is to apply to all Linux distributions. For your own convenience, however, it is strongly advised that beginners stick to a mainstream distribution
, supporting all common hardware and applications by default. The following are very good choices for novices:

- Fedora Core

- Debian

- SuSE Linux

- Mandriva (former MandrakeSoft)

- Knoppix: an operating system that runs from your CD-ROM, you don't need to install anything.

Downloadable ISO-images
can be obtained from LinuxISO.org. The main distributions can be purchased in any decent computer shop.

## Summary

In this chapter, we learned that:

- Linux is an implementation of UNIX.

- The Linux operating system is written in the C programming language.

- De gustibus et coloribus non disputandum est: there's a Linux for everyone.

- Linux uses GNU tools, a set of freely available standard tools for handling the operating system.

## Exercises

A practical exercise for starters: install Linux on your PC. Read the installation manual for your distribution and/or the Installation HOWTO and do it.

### Read the docs!

Most errors stem from not reading the information provided during the install. Reading the installation messages carefully is the first step on the road to success.

Things you must know BEFORE starting a Linux installation:

- Will this distribution run on my hardware?

  Check with http://www.tldp.org/HOWTO/Hardware-HOWTO/index.html when in doubt about compatibility of your hardware.

- What kind of keyboard do I have (number of keys, layout)? What kind of mouse (serial/parallel, number of buttons)? How many MB of RAM?

- Will I install a basic workstation or a server, or will I need to select specific packages myself?

- Will I install from my hard disk, from a CD-ROM, or using the network? Should I adapt the BIOS for any of this? Does the installation method require a boot disk?

- Will Linux be the only system on this computer, or will it be a dual boot installation? Should I make a large partition in order to install virtual systems later on, or is this a virtual installation itself?

- Is this computer in a network? What is its hostname, IP address? Are there any gateway servers or other important networked machines my box should communicate with?

  ### Linux expects to be networked

  Not using the network or configuring it incorrectly may result in slow startup.

- Is this computer a gateway/router/firewall? (If you have to think about this question, it probably isn't.)

- Partitioning: let the installation program do it for you this time, we will discuss partitions in detail in . There is system-specific documentation available if you want to know everything about it. If your Linux distribution does not offer default partitioning, that probably means it is not suited for beginners.

- Will this machine start up in text mode or in graphical mode?

- Think of a good password for the administrator of this machine (root). Create a non-root user account (non-privileged access to the system).

- Do I need a rescue disk? (recommended)

- Which languages do I want?

The full checklist can be found at http://www.tldp.org/HOWTO/Installation-HOWTO/index.html.

In the following chapters we will find out if the installation has been successful.