The history of Unix and Linux you don't know

Date: Oct 25, 2022

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Abstract: The relationship between UNIX and Linux is an interesting topic. Among the current mainstream server-side operating systems, UNIX was born in the late 1960s, Windows was born in the mid-1980s, and Linux was born in the early 1990s. It can be said that UNIX is the "big brother" in the operating system. Both Windows and Linux later referenced UNIX.

The bumpy history of UNIX

The UNIX operating system was invented by Ken Thompson and Dennis Ritchie. Part of its technical origins can be traced back to the Multics engineering program started in 1965, which was initiated by Bell Labs, the Massachusetts Institute of Technology and General Electric Company with the goal of developing an interactive, multi-programming program. A time-sharing operating system capable of replacing the batch operating system that was widely used at the time.

In the 1960s, that computer was not very popular, only a few people could use it, and the computer systems at that time were all batch processing, that is, a batch of tasks were submitted to the computer at one time, and then waited for the result. And can not interact with the computer in the middle. It often takes a long time to prepare for the homework, and others cannot use it at this time, resulting in a waste of computer resources.

Description: The time-sharing operating system enables one computer to serve multiple users at the same time, and the terminal user connected to the computer issues commands interactively. The system divides the CPU time into several segments, called time slices). The operating system takes time slices as a unit and serves each end user in turn, one time slice at a time.

However, due to the complexity of the Multics project and the slow progress of the project due to other reasons, Bell Labs felt that the project might not be successful in 1969, so it quit playing.

After Bell Labs withdrew from the Multics program, the scientists at Bell Labs had nothing to do. One of them, Ken Thompson, wrote a game called Space Travel when he was developing Multics, which is probably A very simple jerking game, but this game runs on Multics. When Bell quit Multics, Thompson had no Multics environment. In order to continue the game, he spent a month writing a small operating system to run Space Travel. After completion, Thompson was pregnant with Excitedly, he called his colleagues over and asked them to play his game. After playing, everyone expressed that they were not interested in his game, but were very interested in his system. The operating system at this time was still written in assembly language.

Because MULTICS is the abbreviation of "Multiplexed informtion and Computing Service" (multiplexed information computing system), they named this system: "UNiplexed Information and Computing Service", abbreviated as "UNICS" (unknown information computing system, the opposite of Multics) ). Later, everyone took its homonym and called it "UNIX".

This time is already 1970, so 1970 is set as the first year of Unix, so UTC time is calculated from this year.

Later, Unix, a small operating system, became popular in Bell Labs, and after continuous improvement, Unix developed to its fifth version in July 1974. Bell Labs made Unix public, which aroused widespread interest in the academic community and Ask for its source code. Therefore, the fifth version of Unix was provided to universities for teaching purposes under the agreement of "for educational purposes only", and it became an example teaching material for operating system courses at that time. Universities and companies began to make various improvements and extensions to Unix through Unix source code. In 1978, the leader of the academic world, Berkeley University, launched a version of Unix based on the sixth edition, plus some improvements and new features. And named BSD (Berkeley Software Distribution Berkeley Distribution), created another branch of Unix: BSD series, which is the famous "1 BSD (1st Berkeley Software Distribution)".
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As a result, Unix has two branches, one is the branch of the BSD series, and the other is the branch issued by Bell itself. At that time, because Bell belonged to AT&T, AT&T was affected by the US "Sherman Antitrust Law" and could not sell anything but telephones. Commodities other than electromechanical telegraphs, etc., were later broken down by AT&T, Bell could sell Unix, and Unix became commercialized. If you want to continue to use it, you need to buy a license, and a license is 40,000 US dollars.

The birth of C language is inseparable from the development of Unix. As mentioned earlier, from 1969 to 1970, Ken Thompson and Dennis Ritchie of Bell Labs in the United States used assembly language to write the first version of the UNIX operating system.

Due to the good performance of the UNIX operating system, it was rapidly popularized and applied in the early days of its release. In 1973, when KenThompson and DennisRitchie were doing system kernel porting development, they felt that it was difficult to use assembly language. Later, they decided to use a language called BCPL (BasicCombinedProgrammingLanguage) for development. During the development process, they made further improvements on the basis of BCPL and launched the B language (take the first letter of BCPL).

Later, it was found that the UNIX kernel developed using the B language still could not meet their expected requirements, so on the basis of the B language, further improvements were made to design a programming language with rich data types and support for a large number of operators. The improved language is a qualitative leap compared to the B language, named as the C language, and successfully re-written the UNIX kernel using the C language.

So far, the UNIX version of the kernel written in C language has been quite stable and has good portability, laying a solid foundation for the further promotion and popularization of UNIX, and also showing the perfect combination of C language and UNIX and the C language in writing System software is a unique advantage.

By 1973, most of the source code of the UNIX system was rewritten in C language, which was the third version of UNIX, which laid the foundation for improving the portability of the UNIX system (the previous operating systems mostly used assembly language, Strong dependence on hardware), which also creates conditions for improving the development efficiency of system software. It can be said that the UNIX system and the C language are twin brothers and have an inseparable relationship.

In the early 1970s, there was another great invention in the computer world - the TCP/IP protocol, which was a network protocol developed after the US Department of Defense took over ARPAnet. The U.S. Department of Defense bundled the TCP/IP protocol with the UNIX system and the C language, and was issued a non-commercial license by AT&T to various universities in the United States, which kicked off the development of the UNIX system, the C language, and the TCP/IP protocol. They have influenced the three fields of operating system, programming language, and network protocol respectively. Ken Thompson and Dennis Ritchie received the Turing Award, the highest award in computer science, in 1983 for their outstanding contributions to the field of computing.

Subsequently, various versions of UNIX systems appeared, such as Sun Solaris, FreeBSD, IBM AIX, HP-UX and so on.

AT&T and BSD disputes

As mentioned earlier, in 1978, the leader of the academic world, Berkeley University (UC Berkeley), launched a Unix based on the sixth edition, plus some improvements and new features.

In 1979, AT&T launched the seventh edition of System V, which supported the x86 architecture. But at the same time, it is specially stated that "the source code cannot be provided to students".

Although AT&T's Unix System V is also a very good version of Unix, BSDUnix has a greater influence in the Unix world. AT&T's Unix Systems Lab has been following the development of BSD, and in 1992, Unix Systems Lab accused BSDI, a company that distributes commercial BSD Unix, of violating AT&T's licensing rights by releasing its own version of Unix, and further charged Berkeley Computer The Systems Research Group leaked Unix trade secrets (at this time, less than 10% of the code from AT&T Unix in 4.3BSD was available).

This lawsuit has affected many Unix manufacturers, making them have to switch from BSD Unix to UnixSystem V to avoid legal problems. So much so that most commercial Unix versions today are based on Unix System V.

With the final verdict pending, the legal action delayed the development of BSD descendants, especially free software, for two years, which resulted in a great support for the Linux kernel without legal issues. Linux started around the same time as 386BSD development, and Linus said he probably wouldn't have created Linux if there had been a free 386-based Unix-like operating system at the time. Although it is impossible to predict what impact this will have on the future software industry, one thing is certain, Linux has enriched this soil.

The lawsuit continued until AT&T sold its Unix system labs, and it was already 1993, when the newly acquired Novell took a more enlightened approach, allowing BSDI to freely distribute its own BSD, but only if it had to The code from AT&T was completely removed, and the 4.4 BSD Lite version was born. Since there were no legal issues with this version, 4.4BSD Lite became the basic version of modern BSD systems.

Since the BSD system is already very mature, as the goal of research on the operating system has been achieved, the Berkeley Computer Systems Research Group (CSRG) was disbanded after the release of 4.4BSD-lite2. Some researchers in the group entered Unix commercial companies, and some Continue research in other areas of computing. At this point, Unix System V and BSDUnix in the strict sense no longer exist, only their various follow-up versions exist. Since then, BSD Unix has embarked on a revival road. Development of BSD also went in several different directions, eventually leading to FreeBSD, OpenBSD, and NetBSD.

The copyright for Unix was once owned by AT&T, then Novell owned Unix, and then Novell sold the copyright to SCO (a fact that is still disputed). There are many large companies that have developed their own Unix products after licensing Unix.

Open Source Leader - Stallman

AT&T's commercial attitude of no longer developing source code made many Unix enthusiasts and software developers feel quite distressed and worried at that time. They believed that various restrictions on commercialization were not conducive to the development of production, on the contrary, it could lead to There are many problems with the manufactured products. With the various limitations and problems of the commercial Unix version, it has caused dissatisfaction and opposition from the public. As a result, everyone began to form a "rebel alliance" in an organized way to fight against commercial behaviors such as AT&T, which were bullying and striking the market.

On the other hand, the contrast between the two development models of "cathedral" (centralized, closed, controlled, confidential) and "bazaar" (decentralized, open, and refined peer review) has become the central idea of ​​the new trend of thought. This new trend of thought has had a very far-reaching impact on the IT industry. Bringing revolutionary values ​​to the entire computer world.

At this time, a leader named Richard Stallman appeared. He believed that Unix is ​​a very good operating system. If everyone can contribute what they have learned, then this system will be even more excellent! The concept of Open Source advocated by him is against the fact that Unix opposes the commercialization and privatization of products in the laboratory.

Although Stallman was neither and never became a Unix programmer, in the post-1980s environment, implementing a Unix-like operating system became a clear strategic goal he pursued. Richard Stallman's early donors were mostly veteran ARPANET who were new to Unix ground, and their commitment to code sharing was even stronger than those of those with more Unix backgrounds.

For this ideal, Richard Stallman founded GNU in 1984, planning to develop a set of software compatible with Unix. In 1985 Richard Stallman founded the Free Software Foundation (Free Software Foundation) to provide technical, legal and financial support for the GNU project.

Although the GNU project is mostly a voluntary, unpaid contribution of individuals, the FSF sometimes hires programmers to help write it. As the GNU Project began to gain ground, some commercial companies stepped in for development and technical support. The most famous of these is Cygnus Solutions, which was later acquired by Red Hat.

The establishment of the GNU organization continued the situation when Unix first appeared, and established reliable legal and financial guarantees for this situation. For more than ten years, the GNU Project has become a major influence on software development, creating countless important tools. For example: a robust compiler, a powerful text editor, or even a full-featured operating system. Since then, many programmers have come together to develop a free, high-quality, easy-to-understand software that keeps the Unix community alive and thriving.

Since this project was initiated in the 1990s, GNU has started to generate or collect a large number of necessary components for various systems, such as - function libraries (libraries), compilers (compilers), debugging tools (debugs), text editors ( text editors), a web server, and a Unix user interface (Unix shell), etc., etc.

But for various reasons, GNU has not developed the kernel of the operating system. While Richard Stallman was struggling with the operating system kernel, Linux came along. It is because of Unix's closed source line that Linux was born, Linus Torvalids created Linux in 1991 - this is not a simple Unix clone, but it looks like Unix (system structure and function), the kernel It has been integrated with the GNU suite to form today's various Linux distributions.

GNU

The GNU Project, also known as the GNU Project, was publicly launched by Richard Stallman on September 27, 1983. Its goal is to create a completely free operating system. Richard Stallman first announced the news on the net.unix-wizards newsgroup, accompanied by an article such as the "GNU Manifesto" explaining why the project was launched. One of the reasons was to "recreate the solidarity spirit of cooperation and mutual assistance in the software industry. ".

To ensure that GNU software is free to "use, copy, modify, and distribute", all GNU software is licensed under the terms of a license that grants all rights to anyone without adding any restrictions to others, the GNU General Public License ( GNU General Public License, GPL). That is "anti-copyright" (or Copyleft) concept.

Introduction

GNU is a recursive acronym for "GNU's Not Unix". Stallman announced that GNU should be pronounced Guh-NOO to avoid confusion with the word new. UNIX is the name of a widely used commercial operating system. Since GNU will implement the interface standard of the UNIX system, the GNU project can develop different operating system components separately. The GNU project adopted some software that was already freely available at the time, such as the TeX typesetting system and the X Window system. However, the GNU Project has also developed a large number of other free software.

History

In 1985 Richard Stallman founded the Free Software Foundation (Free Software Foundation) to provide technical, legal and financial support for the GNU project. Although the GNU Project is mostly a voluntary, unpaid contribution of individuals, the FSF sometimes hires programmers to help write it. When the GNU project began to gain ground, some commercial companies began to step in for development and technical support. The most famous of these is Cygnus Solutions, which was later merged by Red Hat.

By 1990, the GNU Project had developed software that included a powerful text editor, Emacs. GCC (GNU Compiler Collection, GNU Compiler Collection), is a set of programming language compilers developed by GNU. And most UNIX system libraries and tools. The only important component that remains unfinished is the operating system's kernel (called HURD).

In 1991, Linus Torvalds wrote a UNIX-compatible Linux operating system kernel and released it under the terms of the GPL. After Linux was widely circulated on the Internet, many programmers participated in the development and modification. In 1992, when Linux was combined with other GNU software, a completely free operating system was officially born. The operating system is often referred to as "GNU/Linux" or simply Linux. (Nevertheless, the GNU Project's own kernel, Hurd, is still in development and is currently in beta.)

GNU software is also installed on many UNIX systems because the quality of GNU software is better than that of previous UNIX software. GNU tools are also widely ported to Windows and Mac OS.

Linux distribution

We know that Linux or Unix is ​​an operating system. In 1991, Linus Torvalds announced the Linux kernel (kernel). But it should be noted that the source code is published, not a compiled and directly installable operating system. How do we install an operating system? It's very simple, just download a source code first, then compile and install it, but when compiling, the program needs to run on the operating system. What about the operating system? Haven't compiled yet. So we fell into an infinite loop, that is, if we want to install the operating system, we need to compile, and the operating system is required when compiling, so the chicken lays the egg, and the egg lays the chicken.

Here we need to introduce cross-compilation. The specific method is to assume that we want to install Linux on the computer. We remove the hard disk of A, put it on the computer B where the operating system has been installed, and then compile, and put the compiled operating system on the computer. To the hard disk, then put the hard disk back, boot up, this is the cross-compilation installation system.

How hard is this, the difficulty of getting started is too high, so we desperately need an easy way to install. So there is a company that collects and compiles the publicized Kernel (kernel) plus some open source peripheral software into secondary files and puts them on the Internet for others to use. Among them, Red Hat (Red Hat) is the One of the famous ones. We know that Linux follows the GPL protocol, which is open and free, so how do they make money? Since you can't sell software, then you can sell services. For example, if a Linux vulnerability is found, then Red Hat will fix it. If you buy our service, we will give you the patch and guide you to install it. All problems will help you. solve.

There is always a shortage of good people in the world. Since RedHat can do this, why can't there be good people doing it for free? Yes, there is such a community, they take the source code of RedHat, and then compile it into an operating system and release it. This is CentOS, which is the community version of RedHat, so a month after the basic RedHat patch package was released, CentOS appeared corresponding. Patch pack. Is this a good or bad thing for Red Hat? This is probably only known to the parties involved, but in early 2014, news came that RedHat had incorporated the CentOS team. Just like MSDN I TELL YOU are all genuine Microsoft software, which can be downloaded at will, but isn't this also a free publicity for Microsoft?

Solaris and FreeBSD

Let's focus on Solaris, an important fork of the UNIX system. Solaris can run on x86 CPU platforms in addition to SPARC CPU platforms. In the server market, Sun's hardware platform has high availability and high reliability, and is the dominant UNIX system in the market.

For users who have difficulty accessing Sun SPARC architecture computers, Solaris x86 can be used to experience the commercial UNIX style of world-renowned manufacturers. Of course, Solaris x86 can also be used for servers for actual production applications, and Solaris x86 can be used free of charge for study, research or commercial applications, subject to Sun's relevant licensing terms.

FreeBSD originated from the UNIX version developed by the University of California, Berkeley. It is developed and maintained by volunteers from all over the world, providing different levels of support for computer systems with different architectures. FreeBSD is released under the BSD license agreement, which allows anyone to use and distribute freely on the premise of retaining copyright and license agreement information, and does not restrict the distribution of FreeBSD code under another agreement, so commercial companies can freely integrate FreeBSD code into in their products. Apple's OS X is an operating system based on FreeBSD.

A considerable part of the user groups of FreeBSD and Linux overlap, the hardware environments supported by the two are also relatively consistent, and the software used is relatively similar. The biggest feature of FreeBSD is stability and efficiency, and it is a good choice as a server operating system; however, its hardware support is not as complete as Linux, so it is not suitable as a desktop system.