1、1.1. History1.1.1. UNIXIn 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 ha

2、d a different operating system. Software was always customized to serve a specific purpose, and software for one given system didnt run on another system. Being able to work with one system didnt automatically mean that you could work with another. It was difficult, both for the users and the system

3、 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 of IT was enormous.Technologically the world was not quite that advanced, so they had to live with the size for

4、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 wassimple and elegantwritten in the C programming language instead of in assembly co

5、deable 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 spe

6、cial 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,

7、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 effort

8、lessly. 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 diff

9、erent 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 th

10、at 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 80s, many people had home computers. By that time, there were several ve

11、rsions of UNIX available for the PC architecture, but none of them were truly free.1.1.3. Current application of Linux systemsToday 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

12、 taken down. We dont 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, spreads

13、heets, 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 such. Especially Internet providers and Internet service

14、 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

15、 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

16、on workstations, mid- and high-end servers, but also on gadgets like PDAs, 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.1.2. The user interface1.2.1. Is Linux difficu

17、lt?Whether Linux is difficult to learn depends on the person youre 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:

18、 compilers, libraries, development and debugging tools. These packages come with every standard Linux distribution. The C-compiler is included for free, 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 b

19、etween 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. . 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 e

20、ven 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

21、 accessibility of the system.1.2.2. Linux for non-experienced usersCompanies such as RedHat, SuSE and Mandrake 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

22、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 app

23、lications 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, wh

24、ile 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 deskto

25、p applications are making incredible efforts to make the most beautiful desktops youve ever seen, or to make your Linux machine look just like your former MS Windows or MacIntosh workstation. The latest developments also include 3D acceleration support and support for USB devices, single-click updat

26、es 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.1.3. Does Linux have a future?1.3.1. Open SourceThe idea behind Open Source software is rather simple: when programmers can read, distribute and ch

27、ange 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

28、 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 technic

29、al 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 h

30、andful 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, upd

31、ates and support and customizations, etcetera. Today, Linux is ready to accept the challenge of a fast-changing world.1.3.2. Ten years of experience at your serviceWhile Linux is probably the most well-known Open Source initiative, there is another project that contributed enormously to the populari

32、ty 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 Linu

33、x. Packages are now available for almost every system and provide interconnection solutions in mixed environments using MS Windows protocols: Windows-compatible (up to and including Win2K) file- and print-servers.Maybe even more successful than the SAMBA project is the Apache HTTP server project. Th

34、e 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 w

35、arfare 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 com

36、munity 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 works

37、tations. These initiatives helped a great deal to make Linux acceptable for the desktop market, because the users dont 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, wh

38、ich 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 a

39、like 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.1.4. Propert

40、ies of Linux1.4.1. Linux ProsA 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 dont even have to pay the price of a CD. Linux can

41、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

42、 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 suppo

43、rt 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 doesnt know what kind of OS his new machine will run (say the CP

44、U 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

45、 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 dont have the time or the possibility to contr

46、ol 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

47、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

48、all. You dont 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 Linu

49、x OS and 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 found very quickly. It often happens that there are only a couple of hours between discovery and fixing of a bug.1.4.2. Linux ConsThere a

50、re 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

51、 or she needs. You dont 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? Dont worry too much about that: all releases contain more or less the same set of ba

52、sic 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

53、 of distributions; unfortunately not everybody has the time for this. Luckily, there is plenty of advice on the subject of choosing your Linux. One place is LinuxJournal , which discusses hardware and support, among many other subjects. The Installation HOWTO also discusses choosing your distributio

54、n.Linux is not very user friendly and confusing for beginners: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 us

55、ers 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 dont have that kind of freedom. After long periods o

56、f 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

57、 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.1.1。 歷史1.1.1。 UNIX為了了解Linux的歷史，我們需要追溯到

58、30年前。想象一下像房子甚至體育館一樣大的計(jì)算機(jī)。 除了電腦的體積帶來(lái)的問(wèn)題，有一件事情讓這些變得更糟糕，那就是每個(gè)計(jì)算機(jī)都有一個(gè)不同的操作系統(tǒng)。軟件定制服務(wù)一直是一個(gè)給定系統(tǒng)的特定目標(biāo)，軟件無(wú)法在另一個(gè)系統(tǒng)上運(yùn)行。能夠在一個(gè)系統(tǒng)下工作并不意味著也可以自動(dòng)同另一個(gè)系統(tǒng)共事。這些無(wú)論對(duì)于用戶還是系統(tǒng)管理員都是非常困難的。由于計(jì)算機(jī)非常昂貴，所以人們不得不為之付出，即使購(gòu)買計(jì)算機(jī)那也只是為了讓用戶了解他們是如何工作的。但是IT的總成本還是非常巨大的。世界上的技術(shù)還沒有那么先進(jìn)，因此他們不得不和如此大的計(jì)算機(jī)共同再度過(guò)十年。 在1969年，貝爾實(shí)驗(yàn)室的開發(fā)團(tuán)隊(duì)人員們開始研究，為解決軟件問(wèn)題，更好的完善兼容性。 他們開發(fā)出一種新的操作系統(tǒng)，就是這個(gè)。簡(jiǎn)單巧妙用C語(yǔ)言設(shè)計(jì)代替匯編碼能夠循環(huán)利用的代碼。貝爾實(shí)驗(yàn)室開發(fā)的項(xiàng)目把它命名為“UNIX操作系統(tǒng)?！痹摯a循環(huán)的功能是非常重要的。在此之前，所有商用計(jì)算機(jī)系統(tǒng)是寫在一個(gè)專門為系統(tǒng)開發(fā)的代碼中。而UNIX只需要有一組特殊的代碼，也就是現(xiàn)在俗稱小片的內(nèi)核。這個(gè)內(nèi)核的代碼是唯一的一塊，需要為每一個(gè)特定的系統(tǒng)和各種形式的UNIX系統(tǒng)基礎(chǔ)改編。操作系統(tǒng)