Brother Bird's Private Kitchen-1 What is linux

Come to think about it, when we use the computer, where does the dong dong displayed on the screen come from? Um! It is displayed by the display card and the screen; then you can now see this article through the network, which is a task completed by the Internet, network cards, network cables and all related electronic equipment and network equipment! What if you want to watch a VCD? Then you need the support of CD-ROM, CD-ROM, sound card and so on. In this way, everything that is "working" is the work of "hardware"! correct! It's the computer hardware that does the work. So how does the hardware work? That is achieved by the "operating system"! This operating system is communicating messages between you, the user, and the hardware! In other words, without an operating system, your computer hardware is just a pile of scrap metal that can't do any work!

Generally speaking, the items managed by the Kernel are:

System call interface: After some services communicate with the kernel, the hardware resources are further utilized; Process control: The system process control center, so the smaller the core code, the better; Memory management: Control Memory management of the entire system; File system management: management of the file system, such as I/O and so on! There is also support for different file formats, etc. If your core does not know a certain file system, then you will not be able to use the files in this file format! For example, Windows 98 mentioned above does not know the hard disk in NTFS file format; Device drivers: As mentioned above, hardware management is one of the main tasks of Kernel. Of course, the driver of the device is what the core needs to do. ! Fortunately, there is currently a so-called "loadable module" function, which can edit the driver into a module, so there is no need to recompile the core! This will also be mentioned in the subsequent core compilation!

The core is the dong dong that controls the support of the entire hardware, and it is also the bottom layer of an operating system. However, to make the entire operating system more complete, it also needs to contain a lot of tools provided by the core, as well as core-related application software to support it!

 Why do people often say that Linux is a very stable operating system in the history of Unix to Linux? This is because Linux has an old predecessor, that is the Unix family! With the help of this senior, Linux, this little brother, will soon become a stable and excellent operating system! So, let's talk about the history of Unix to Linux! Twenty years before Linux (around the 1970s), a fairly stable and mature operating system existed! That is the big brother of Linux "Unix" is also! How do you say that? ! What is the relationship between these two guys? Tell him about it here! As we all know, the core of Linux was developed by Linus Torvalds in 1991 and put it on the Internet for everyone to download. Later, everyone felt that this little thing (Linux Kernel) was quite small and exquisite, so Slowly, quite a lot of friends have invested in the research field of this little thing! But why is this little thing so awesome? ! But why can everyone download this thing for free? ! Um! Wait for Brother Bird to slowly bluff xx... Oh no! Listen to me slowly!


An unfinished dream: Bell, MIT and GE's 'Multics' system 
The early computer was not like the current personal computer. It was not something that ordinary people could touch. Unless it was military or high-tech use, it was possible to come into contact with this kind of Computer! As mentioned earlier, computer hardware also requires the cooperation of the operating system to be able to exert the performance of the computer. However, at that time, since the computer was regarded as a "luxury", oh ~ it should be said to be a "valuable item", so there may be a There was only one mainframe in every school. Of course, the so-called mainframes of that era still couldn't provide moderate computing power. However, since there is only one mainframe, but there are many teachers and students who want to use it, what should we do? In order to solve this problem, in the early 1960s, the Massachusetts Institute of Technology (MIT) developed the so-called "Compatible Time-Sharing System (CTSS)", in the literal sense, he mainly made the mainframe It can provide multiple terminals to connect to the host to use the resources of the host. (By the way, the terminal itself did not have software or available resources at that time. To be able to use these terminals, you must log in to the host online. After that, you can use the host's resources to work!) At that time, about 30 users could be connected to the host. In order to make this time-sharing system more powerful, a large-scale project called Multics was jointly developed by Bell Labs (Bell), Massachusetts Institute of Technology (MIT) and Strange Electric Company (GE) around 1965. , the goal is to allow the mainframe to connect more than 300 users. However, after four years of struggle, the program is still dead... oh! It's a failure! (Note: Multics means complex, many.)


The production of a small file system: Ken Thompson's small file server system in 1969 
After plans for a complex Multics system failed, Bell Labs of course pulled out of the project. Just after the disbandment of this plan, Ken Thompson, a member of Bell Labs who had participated in Muitics, needed a small operating system for file access due to his own work needs. His computer PDP-7 is the hardware benchmark, and he designed a small file system suitable for his working environment, which also contains some small tools developed by him. That system was the source of the earliest Unix! When Ken designed this file system, it was mainly a simple OS designed for his own access convenience, so the original Multics system was greatly simplified. However, the term Unix did not appear at that time!


The official birth of Unix: In 1973, Ritchie and others wrote the first official Unix core in C language. 
Because the operating system written by Thompson was so easy to use, it was widely circulated in Bell's laboratory and was revised several times. In 1973, Dennis Ritchie and others of Bell Labs used the C language with better compilation performance to significantly rewrite the core of the original 1969 system in order to optimize the execution performance of this system, and Make sure the operating system name is Unix, huh! That is the earliest Unix operating system Hello! However, since this operating system was developed by this group of engineers, and most of the users are engineers in this field, it caused the situation that the Unix system interface was difficult to be accepted by general users later @_@ (Note: Relatively With Multics, Unix has a single meaning!)


Important Unix fork: Birth of BSD in 1977 
In the early development of Unix, there is a very important thing, that is the birth of BSD! Since C language is a high-level language, it can be applied to different hardware architectures, and Unix itself is written in C language! After Unix was published, professors at Berkeley University (Berkeley) were very interested in this operating system. After obtaining the source code of Unix and making several modifications, they finally published the first generation of Berkeley Software Distribution (Berkeley Software Distribution) in 1977. BSD). This BSD is a branch of Unix, and its development has a considerable impact on Unix. For example, later Sun Corporation used the core of BSD development to develop its own commercial Unix version!


The Unix version of a hundred schools of thought: 
Since C language is a fairly high-level programming language, it is not directly related to hardware. For example, your Windows can also execute C programming language! And because Unix is ​​written in C language, that is to say, you can execute this operating system on different hardware architectures with only a slight source code modification program! Later, due to the convenience of Unix, many commercial companies and academic institutions joined the research and development of this operating system. However, due to the convenience and ease of rewriting of Unix, there are many different versions of Unix, such as ATT's System V, University of California's BSD version, IBM's AIX and so on. Because "the core of the operating system (Kernel) must cooperate with the hardware to provide and control the resources of the hardware to work well! ”, and in the early days, every company that produced computer hardware did not have the concept of a so-called “protocol”, so the hardware produced by each computer company was naturally different! Therefore, they must develop a suitable Unix system for their own computer hardware, so, of course, their self-developed Unix can only be equipped with their own hardware! For example, Sun, Cray and HP, which are quite well-known in academic institutions, are such a case, they developed Unix and there is no way to work under other hardware architectures! (We all call such systems and equipment "supercomputers")! Since no manufacturer designed Unix systems for personal computers, there was no Unix operating system that supported personal computers in the early days (of course, this was because early personal computers were not as popular as they are now!), each company made its own Although the Unix is ​​similar in structure, it can only support its own hardware, so, the earlier Unix can only be equated with a server (Server) or a large workstation (Workstation)! In addition, because there are too many versions, and everyone is also from the ancestor of Unix, of course, they all call themselves Unix. Well, as a result, many commercial companies will naturally publish similar software, drink! Then naturally there will be some commercial disputes! It's really nerve-racking~

GNU and the Free Software Foundation in 1984: 
The commercial problems of Unix make many Unix lovers feel quite concerned, one of them is the famous Mr. Richard M. Stallman. He believes that Unix is ​​a very good operating system. On this system, if everyone can contribute what they have learned, then this system will be even better! Mr. Stallman believes that the greatest joy is to let everyone use the good software he has developed! Moreover, since everyone's working environment (referring to software and hardware platforms) may be different, he also emphasized that there should be the concept of Open Source, so that everyone can share this experience! He believes that with Open Source, your program will have a lot of people who can help to test it, which will make the Unix community better and stronger. For his own ideals, Stallman actually founded the GNU and Free Software Foundation (FSF) in 1984, and created a lot of "free software" for the public to use. The licensing model of the GNU General Public License (GPL) is available for public use. The core concept of this FSF is that "the copyright system is a means of promoting social progress, and copyright itself is not a natural power. 』If you are interested in FSF or want to have a more in-depth understanding of GNU, please refer to the website of Professor Hong Chaogui of Chaoyang University, which has a more in-depth explanation! Also, Stallman's GNU General Public License always emphasizes the word Free! He said this: ""Free software" is a matter of liberty, not price. To understand the concept, you should think of "free speech", not "free beer". "Free software" refers to the users freedom to run, copy, "freedom" software, what is the degree of freedom? That is, after you obtain this software, you can modify, further publish and copy it on different computer platforms. This is undoubtedly good news! Because of this, the software you get may only run on Unix originally, but after the modification of the original code, you will be able to use it to run on Linux or Windows! Mr. Stallman directly explained the degree of freedom: you can run the Free program according to any proposal (purpose) you want; after you understand the operation of the Free program, you can modify it to The style and function you want; you can publish your own modified Free program again to help your friends; you can improve this Free program and publish the modified program to the public , for the benefit of the community! In simple terms, GPL licensing has several characteristics: after any software is licensed under GPL, it is free software, and anyone can obtain it, and at the same time, the source code can also be obtained; after obtaining GPL-licensed software , anyone can modify the source code to suit their own preferences; in addition, the modified Source Code should be reported to the online community for your reference! But please pay special attention, it is not that the software after the GPL cannot be sold, this is two different things! For example, the Linux installation CD released by Red Hat is available for public download on Red Hat's official website, but Red Hat itself still sells Linux packages, and they also sell "very cheap!" 'Why is this possible? Ha ha! Because the data sold by Red Hat contains a large amount of edited file data, although these data can be downloaded from the Internet, but it took so much time to organize these data, of course, they should be paid to a considerable extent! You say yes! So, please pay attention! It's not that the GPL can't be used for profit! This GNU has a very profound influence on the later Linux. Since Mr. Stallman developed the GNU project, the main force is to launch various convenient and excellent tool software, such as the well-known Emacs document editor, GCC, BASH. . However, how to use these software without a work platform? However, due to the free software he advocated, the later efforts can quickly contact the source code to develop software. This is the story of the later Linux.... This is the later story, wait for it~


Graphical interface X-Free86 project in 1988: 
In view of the increasing demand for Graphical User Interface (GUI), the X Window System was first published by MIT and other third-party manufacturers in 1984, and was established in 1988. The non-profit XFree86 organization. The so-called XFree86 is actually the integrated name of X window system and Free and x86 system architecture! And the GUI interface of XFree86 was integrated into the Linux operating system when the Linux kernel version 1.0 was released in 1994!


A note from Linus Torvalds, a Finnish university student in 1991: 
In the next few years, due to the strong operation of the computer hardware industry, the personal computer of the x86 system architecture dominated by intel became popular, so the personal computer is quite a popular machine! But at this time, people mostly use the old DOS series or other operating systems that consume a lot of system resources. At this point, a student from Linus Torvalds at the University of Helsinki in Finland did something unusual! Linus has a Minix system at hand (which is also a fork of Unix), and he is quite interested in this operating system! Besides, since he happened to buy a 386 computer at the time, he just wanted to say, Huh! This Unix is ​​so awesome! So stable, can I port it to a personal computer (X86 architecture) to use it? ! Fortunately, due to the Open Source ethos advocated by Stallman, he was able to get in touch with some source code, and through such an idea, huh! He read the core of Unix very attentively, and removed the more complicated core programs, and rewrote it into an x86 system that can be applied to general personal computers. In 1991, he finally put the 0.02 version of hobby on the Internet for Everyone downloaded, and because hobby was affirmed by everyone, quite a lot of friends put into this work together! Finally in 1994 the first full core Version 1.0 was released! And caused the current pandemic... Since the development of the Linux kernel is achieved by the "virtual team", everyone obtains the core source code of Linux through the network, and then passes it back to the Linux community after careful transformation. Group, and then developed step by step to complete a complete Linux system, as Mr. Torvalds is the initiator of this group. As a result of this collective effort, Mr. Torvalds made Linux a GNU licensing model that also benefits everyone!


Source of Penguin: 
When the official Linux kernel 1.0 was released in 1994, everyone asked Linus Torvalds to think of a mascot. Torvalds suddenly thought of going to the zoo when he was a child and being chased by a penguin and rolling around on the ground~ and got bitten! Since I can't think of other mascots, let's just use this penguin as the mascot! So, hehe! At present, we often see this penguin just like this!

What is distribution
Red Hat, OpenLinux, Mandrake, Debian, SuSE, etc., so many people are worried, so each distribution is different? This is no need to worry, because each distribution is based on the Linux Kernel to develop its own company-style distribution, so everyone abides by the Linux Standard Base (LSB) specification, that is to say, each distribution is actually similar! Anyway, the Linux Kernel is used! It's just that the suites used in each distribution may not be exactly the same. So, you can choose the distribution CD of Linux according to your own preferences! Listed below are several major Linux distribution sites: Red Hat: http://www.redhat.comMandrake: http://www.linux-mandrake.com/en/Slackware: http://www.slackware.com /SuSE: http://www.suse.com/index_us.htmlOpenLinux: http://www.caldera.com/Debian: http://www.debian.org/Linpus: http://www.linpus.com .tw/UniteLinux: http://www.sco.com/unitedlinux/

Of course the distros don't stop there, you can check other Linux news to find out! Among them, the more famous Chinese culture is the publisher of the CLE suite! In addition, there is another Linux developer in Taiwan, called Linpus (Hundred Capital), if you are interested, you can also take a look at the website below! CLE: http://cle.linux.org.tw/100-funded: http://www.linpus.com.tw/ Well, which installation kit is better? ! As mentioned earlier by VBird, the Linux kernel used by each issuer is actually the same, which is the kernel developed by www.kernel.org! So its structure, even including the directory where its files are placed, are similar, basically except for some content packages that are not the same (for example, some people use wu-ftpd, some people use proftpd, etc.), other file structures and command systems It's actually pretty much the same, so we're not going to discuss which kit is better! Rather, it's about how to learn and use a kit! As for the download location, netizens have provided a very good download site for a variety of Linux distributions: www.linuxiso.org At the same time, the website below also has a comparison of various famous Linux distributions! Including the popularity of use, market share, and the degree of dependency of the suite, etc.:

http://www.distrowatch.com/

Linux features and advantages and disadvantages The origin of Linux: 
As mentioned earlier, Mr. Linus Torvalds has always liked that A small operating system core, and the core is the bottom layer of managing a system, and all hardware resources are controlled by the kernel! However, as mentioned earlier, the early Unix did not support the x86 personal computer architecture, and it was not until 1991 when Mr. Linus posted a small notice in the BBS that there was a major change: Hello everybody out there using minix- 
I'm doing a (free) operation system (just a hobby, 
won't be big and professional like gnu) for 386(486) AT clones. This BBS email was published by Linus Torvalds, a college student who was still in Finland at the time, he said that he modified a simple operating system core, the core Named hobby, the core of this hobby ( Kernel ) is the first Linux core system! In addition, since he developed this operating system based on the GNU protocol, it is Free and anyone can download and use it! (Note: hobby is a personal interest, just a hobby, won't be big and professional like gnu, which means: just a personal interest, not as big as gnu~~~) This hobby developed by Linus It was developed based on the Unix system. He simplified a lot of data in Unix and made it applicable to the x86 system dominated by intel (the original personal computer system was 386 and 486 architecture), so he originally The latest system core published is called linus's unix, or Linux for short! Of course, because this core is very similar to the Unix system at that time, it is also called a Unix-like system! (Note: In fact, Unix-Like can be said to be the general name of the current server type operating system! Because, whether it is FreeBSD, BSD, Sun Unix, SCO Unix, HP Unix, Red Hat Linux, Mandrake Linux, etc., all came from the same ancestor "Unix", therefore, these dong dongs are collectively referred to as Unix-Like operating systems! ) So what is the special function of this system? Simply put: Free: Because it is based on the GPL (General Public License) structure, it is Free, which means that anyone can use or modify the source code for free! This is called an "open architecture", and it's quite important to the scientific community! Because many engineers often need to modify the source code of the system due to special needs, so that the system can meet their own needs! And this open architecture will be able to meet the different needs of engineers! So of course it may become more and more popular! Low equipment requirements: while he can support the X86 architecture of personal computers, the system resources do not have to be like the earlier Unix systems, only suitable for a single company (eg Sun) equipment! Just from this point of view, it can cause great popularity! Powerful and stable: And because the function is not lost to some large-scale Unix workstations, more and more companies, groups, and individuals have invested in the development and integration of this operating system in recent years! Independent work: In addition, since many software suites are gradually used by this operating system, and many software suites are also developed and tested on the Linux operating system, Linux has recently been able to complete almost all workstations or Server services, such as Web, Mail, Proxy, FTP..... . Therefore, he is already a fairly mature operating system at present! And it does not consume resources and is free, huh, it can be said to cause considerable pressure on Microsoft! In addition, due to his low system hardware requirements, plus a lot of people are currently due to "Intel conspiracy" (huh! Just kidding, because Tom's hardware review site often says this is not Intel's! Huh! It's funny!) There are quite a few obsolete hardware equipment at hand, and Linux can execute quite smoothly and stably on these obsolete hardware! Therefore, it has also caused a lot of friends' attention! This is also the reason why Linux has become one of the most watched operating systems in recent years. As mentioned above, the reason why it will attract attention is mainly because it is "free", that is, a free operating system! Then he is an open system, that is, you can get the source code of the program at any time, which is very important for program development engineers! And, although it's free, it's powerful! In addition, Linux's demand for hardware is very low, which is the main reason for its popularity. Because the replacement rate of hardware is too fast, many people have some seldom-used parts on hand. These parts are grouped together. It can be used to run Linux. Anyway, you don't need to use the screen to make a workstation (as long as the host is OK), so Linux is becoming more and more popular! (Stop talking, that is, because Linux has 1. low hardware requirements, 2. open architecture, 3. strong system stability and confidentiality, and 4. completely free, so some so-called "anti-Microsoft alliance" programming is caused The masters are constantly developing new software! To compete with Microsoft!) The advantages of Linux: It is completely free, so some so-called "anti-Microsoft alliance" programming experts continue to develop new software! to take on Microsoft! ) Linux advantages: It is completely free, so some so-called "anti-Microsoft alliance" programming experts continue to develop new software! to take on Microsoft! ) Linux advantages: 
So why use Linux as our host system? This is because Linux has the following advantages: Stable system: Linux is an operating system developed on Unix. Therefore, Linux has a program interface and operation method similar to that of Unix. Of course, it also inherits the stability and advantages of Unix. Efficiency characteristics. It is common to hear that a host with Linux installed continuously runs for more than a year without crashing or shutting down; free or a little fee: Since Linux is a product based on the GPL, anyone can freely obtain Linux , As for the publishers of some "installation kits", the installation CDs they issue can be obtained for only a small fee! Unlike Unix, you need to pay huge copyright fees, and of course it is different from Microsoft, which needs to update your system again and again, and pay a lot of fees! Security, vulnerability patching: If you play the Internet a lot, then the most common thing you hear should be "there is no absolutely secure host"! That's right! However, due to the increasing number of supporters of Linux, there are quite a number of enthusiastic groups and individuals involved in the development, so you can get the latest security information at any time, and give updates at any time, that is, it is relatively safe! Multi-tasking and multi-user: Different from the Windows system, the Linux host can allow multiple people to work online at the same time, and the distribution of resources is more fair, which is much more stable than the Windows single-person fake multi-tasking system! This multi-tasking is a very good feature on Unix-Like, how can I say it? You can plan users of different levels on a Linux host, and each user can log in to the system in a different working environment. In addition, you can allow different users to log in to the host at the same time, so that at the same time Use the host's resources. User and group planning: In a Linux machine, the attributes of a file can be divided into parameters such as "readable, writable, executable" to define the applicability of a file. In addition, these attributes can also be divided into three The types are "file owner, group to which the file belongs, other non-owners and group". This provides fairly good system confidentiality to project plan or other plan developers. Relatively less resource-intensive system: Linux can be installed on a p-100 or higher computer and is a pleasure to use! No need to go to P-III yet Class computer! However, if you want to set up a large-scale mainframe (mainframe system serving more than 100 people), then you need a better machine. However, any personal computer currently on the market can meet this requirement!



Disadvantages of Linux: The 
benefits of Linux are endless anyway! However, although Linux has so many advantages, it has a fatal place innately, which greatly limits its popularity, that is, Linux needs to use the terminal mode of the "command line" to manage the system! Although a lot of graphic interfaces have been developed and used on Linux in recent years, it is better to be familiar with Linux or use the command line. Therefore, players who want to accept Linux must be more familiar with the behavior of giving instructions to the computer, not Just click the icon with the mouse and that's it! But what if you just want to set up some simple small stations? Can everyone do it? That's right! In fact, as long as you make some small settings for Linux, you can stand! There is no specific support manufacturer: because all the kits are free, naturally there is no special person who will come to the house to serve it! However, there is no need to worry about this, because thanks to the popularity of the Internet, almost all the questions you want to ask can be answered on the Internet! See if you are looking for it carefully! The graphical interface is not good enough: in fact, it is because VBird doesn't play X-window, so I don't know how far it has developed! Basically, what VBird often says is: "What's on Windows can be found on Linux too! , but Linux has some services that Windows may not have! 』But, you have to find the interface you want by yourself! Some terms (GNU, GPL??) Linux Standard Base ( LSB ) 
Since Linux is a new thing without a "standard product" style, if everyone plays their own, it is conceivable that manufacturers who want to develop software and hardware on the Linux operating system in the future will definitely be at a loss. ! In order to let software developers and hardware developers have a direction to follow, the Linux Standard Base was born! Therefore, each distribution must also follow the specifications above the LSB, and software and hardware developers will also follow the LSB. Therefore, we will often say that although the tools and ideas provided by the major distributions are different, basically, Their Linux architectures are all very similar! So, all you have to do is play with one Linux distribution! Other distributions shouldn't be too difficult for you! Unix-Like 
In fact, Unix-Like can be said to be the general name of the operating system of the current server type! Because, whether it is FreeBSD, BSD, Sun Unix, SCO Unix, HP Unix, Red Hat Linux, Mandrake Linux, etc., all come from the same ancestor "Unix", these dongdongs are collectively referred to as Unix-Like the operating system! At present, when a lot of software is being developed, basically, it can already be used on various Unix-Like platforms! Great, change some source code and it will work for your platform! Servers, workstations, terminals... 
Due to the prevalence of the Internet, we may often hear some terms ㄋ ㄟ ~ so, let's introduce some simple Internet terms first! ^_^, come to know what is a server (Server), workstation (Workstation) and terminal (Ternianl)? To put it simply, you can think of it this way: Server: A host that provides more than one network service on the Internet. For example, if yahoo provides WWW services, then yahoo can be called a server! So, what about setting up a mail server yourself? Ha ha! That's a small server too! Therefore, you must know clearly that the server is divided into different sizes! At present, multiple server software can be set up on one Linux! For example, Apache software of WWW server, Wu-ftp software of FTP server, etc.; Workstation: Basically, a workstation can be regarded as a machine that only provides a group of specific people for numerical analysis and scientific purposes. For example, there is a Sun machine in our research room, which only provides the connection of a few computers in our research room. When we need to use the Fortran programming language, we will enter the Sun machine online and perform what we need on it. Calculations work! This is the workstation. The difference between a workstation and a server probably lies in whether it provides services on the internet. For example, if I open the mail server on Sun, then this machine can be called a server! It is also our workstation! Of course, the broader definition is that as long as there is no network service provided to the Internet, it is a workstation! This of course also includes the so-called terminal! Terminal (Terminal): Simply put, it is the computer in front of the end-user (that's you)! Oh, for example, I use my work machine (Windows) to connect to our host computer to work, then this Windows computer can be called a terminal machine! However, in a more narrow sense, the "terminal" itself should not have any software that can work, and the terminal must be connected to the server. After that, you can do all the work! That is the narrowest terminal! Such as the early mainframe online mode we talked about earlier! Roughly the difference can be seen from the above point of view! Several common authorization modes and definitions 
Let’s talk about a few common licensing models: GNU General Public License: This can be understood from the description just now. It is mainly defined on “free software”. Any software licensed under GPL needs to publish its source code (Open Source) , GPL has several main general directions: any individual or company can release free software (free software); any individual or company releasing free software can charge appropriate fees for its own services; the original software of the software The code (Source Code) needs to be attached to the software, and it can be published publicly; anyone can obtain this free software through any normal channel, and can obtain this licensing model. Freeware: Unlike Free software, Freeware is "free software" rather than "free software! 』Although he is a free software, but not necessarily to publish its source code, depending on the opinion of the releaser! This thing is not the same thing as Open Source after all! In addition, many programs currently advertised as free software have many small problems! For example, under the guise of free software, the purpose of implementing user data theft! So "Do not install software from unknown sources! 』Shareware: The term shareware is interesting! Similar to free software, Shareware is also free at the beginning of its use, but after the so-called "trial period", you have to choose the fate of "continue to use it after payment" or "remove it"~ Often, these shareware programs write their own deactivation procedures that prevent you from using the software after the trial period. Berkeley Distribution Software (BSD): The BSD licensing model is the most common way to use BSD source code! This licensing model is actually very similar to GPL, and its spirit echoes Open Source! Open Source: Open source means that when the software is released, it must be accompanied by the release of the source code! Usually he has several advantages: programmers usually wait until the program is mature before releasing it (to avoid being laughed at, ^_^ ), so usually when the program is in its infancy, it already has a very good physique; in the spirit of Open Source, it is believed that when the original program designer releases the program source code, other programmers will accept this source code After that, since you need to change the program to the style you need, you will improve it through what you have learned, and then improve and deworm from it, so the debug function of the program will come faster than the traditional close source! Since the program is accompanied by the original code, the system will be less likely to have little-known Trojan programs or some security holes, and relatively speaking, it will be more secure! Close Source: The core of the program is closed, the advantage is that it is maintained by a special person, and you do not need to change it; the disadvantage is that the flexibility is greatly reduced, and users cannot change the program to the style they want. In addition, if there is a Trojan horse Program or security holes, it will take a long time to debug! GNU General Public License (GPL) 
We mentioned above that Linux is based on GPL and allows the public to make maximum use! So what is the GPL? Basically he is based on the GNU architecture! To put it simply, GNU means "free software". "Free software" is software that is placed on the Internet for people to download and use for free. Basically, it will provide the original program code and the compiled executable file (some only provide the original code, you have to compile it yourself), and encourage users to modify the program to meet the user's own service needs. Of course, if you modify these free software and sell it in a commercial way, it will not be offended. What legal responsibility is it, but this is a violation of the creative intention of free software! In the current Taiwan education circle, there is a group of teachers who are also actively engaged in the collective creation of this kind of "free software"! This will help Taiwanese primary and secondary school teachers' computer proficiency and provide a good learning environment too! It's really good! The Chinese translation of GNU/GPL is attached below, you can take a look at it!

Basic idea
The basic idea of ​​Linux has two points: first, everything is a file; second, every software has a definite purpose. The first one is that everything in the system boils down to one file, including commands, hardware and software devices, operating systems, processes, etc. For the operating system kernel, they are regarded as files with their own characteristics or types . As for saying that Linux is based on Unix, it is largely because the basic ideas of the two are very similar.
Completely free
Linux is a free operating system, users can obtain it for free through the Internet or other channels, and can modify its source code arbitrarily. This is something no other operating system can do. It is precisely because of this that countless programmers from all over the world have participated in the modification and writing of Linux, and programmers can change it according to their own interests and inspiration, which makes Linux absorb the essence of countless programmers and grow continuously.
Fully compatible with POSIX1.0 standard
This makes it possible to run common DOS and Windows programs through corresponding emulators under Linux. This sets the stage for users to move from Windows to Linux. When many users think about using Linux, they think about whether programs that used to be common under Windows will work properly, which relieves their doubts.
Multi-user, multi-task
Linux supports multi-user, each user has his own special rights to his own file device, ensuring that each user does not affect each other. Multitasking is one of the most important features of today's computers. Linux can make multiple programs run simultaneously and independently.
A good interface
Linux has both a character interface and a graphical interface. In the character interface, users can input corresponding commands through the keyboard to operate. It also provides an X-Window system similar to the Windows graphical interface, and users can use the mouse to operate it. In the X-Window environment, it is similar to Windows, which can be said to be a Linux version of Windows.
Support for multiple platforms
Linux can run on multiple hardware platforms, such as platforms with processors such as x86, 680x0, SPARC, Alpha, etc. In addition, Linux is an embedded operating system that can run on handheld computers, set-top boxes or game consoles. The Linux 2.4 kernel released in January 2001 has been able to fully support the Intel 64-bit chip architecture. At the same time, Linux also supports multi-processor technology. Multiple processors work at the same time, which greatly improves the system performance.