Linux refers to a type of software called an operating system that has drawn attention since the fall of 1998. What is this operating system is mediation between hardware, middleware, and application software In other words, applications and middleware perform processing while talking only with the operating system.The typical operating system Linux is one of the operating systems of Windows and Macintosh, but why Linux became a focus of attention, as will be explained below . One of the major features of Linux is that it is (1) free, (2) many of the software developed for UNIX can be used as it is, (3) it is not developed by a single company but centered around programmers all over the world The development speed is very fast because the cooperation actively cooperates with the mistake of the program, ④ Linux is very stable as OS, high quality and well-received support ⑤ With Windows and Macintosh Differences, Linux can be selected from various distribution packages (distributions) suitable for their purpose and purpose because of its rich variety. In case of In this way, Linux is an OS with various features, but the one that shows the biggest feature among them is ""it is free"". ""Free"" in English has two meanings, ""free"" and ""freedom"", but both can apply to this Linux. That is, Linux is an OS that can be obtained by paying for free or CD-ROM creation fee and postage. Normally you need to purchase a license that is the right to use the OS, such as Windows and Macintosh, pay the fee every time you upgrade, while Linux has done a number of upgrades, or copied many times Even if redistribution is done, not only is it not a problem at all, it is rather encouraged. According to a sentence explaining the installation of Linux, it says, ""After installing, you should give Linux CD-ROM to a friend or let's donate to a nearby library"", Linux also supports OS such as Windows It can be said that this is an OS which is more easily and less expensive to obtain. In addition, ""freedom"" in another meaning of ""free"" is Linux ""freedom to change"". In order to guarantee this, when distributing Linux it is necessary to distribute the source code at the same time or make it available. This is because Linux developers Linus released Linux source code on the Internet simultaneously with software announcement. So, why is it important to publish the source code? If any kind of trouble occurs in the software, if the source code is private, we have to wait until the developer fixes the problem. However, if the source code has been released, if someone who noticed earlier fixes the problem and publishes the fix, the problem can be resolved quickly, and the state of comfort always can be maintained. In this way, why Linux is freely distributed and the program can be changed is because the license of Linux is a different license from the general software. Linux license is used based on General Public License (GPL) created by Free Software Foundation for Free Software. The license called GPL stipulates that not only the program but also the source code can be freely distributed, and the change must be distributed freely. In addition, it also stipulates that it is necessary to redistribute the derived program by changing or improving the program adopting the GPL. Another feature of the GPL is that it does not mention about monetary exchange when distributing software, that is, when distributing Linux, even if it is charged or free, it is good is there. That does not mean anyone who pays the fee for free, but for example, setting the fee to collect the cost necessary for CD-ROM creation, adding value added such as support service using telephone and e-mail It is possible to sell it.