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What is Linux?

The history of Linux

The story of Linux began in 1991 with the debut of the personal project of a Finnish student, Linus Torvalds, who creates the core of a new operating system.

Before talking about Linux it would be nice to talk a bit about the history of the Unix kernel that was designed and implemented in the 1960s at Bell Laboratories under the leadership of Ken Thomson and a small group of researchers from these laboratories to be published in 1969 for internal use in these laboratories. The development of the C language by Dennis Ritchie allowed the writing of a version of Unix in this high-level language and therefore portable a priori on any type of machine with a compiler of this language. Some American universities like Berkeley in particular are very interested in it. Labs Bell / ATT seeing Unix become more and more popular and used decide to develop them themselves.

In addition to the "orthodox" versions developed from the kernel provided by Bell laboratories (V7, System III, Xenix, Spix ...), a number of Unix-oid systems have been developed by different companies. In particular the two most important ones:

• Versions that can be related to the Berkeley strain (version 4.2);
• The versions are intended for the System V standard defined by Bell Laboratories.

It is also very important to note the significant efforts made to standardize the system, whether by the publication of this System V standard or by the major European manufacturers grouped in the "Unix-Open-Group" which published a document of standardization fairly close to that of Bell Laboratories. In addition, a number of projects are being carried out around the world (Berkeley, Digital's Ultrix or Bull's Spix) to provide system versions with both the System V version and the version version. Berkeley integrating in particular to the first the socket mechanism of the second. In addition, the efforts made in France under the GIPSI (public interest grouping involving Bull, CENT and INRIA) to develop a multiprocessor version of the system.

Now that we know the whole story of the Unix system, it becomes important to talk about the GNU project. It was in 1983 that Richard Stallman started the GNU project in order to be able to create free UNIX-Oide operating systems. As part of this work he also writes the GNU General Public License (GPL). An interesting little story about GNU, since the early 1990s there is a GNU kernel named Hurd that has unfortunately failed to attract enough attention from developers.

This fabulous story will continue with another free operating system project in the 1980s that is Berkeley Software Distribution (BSD). This was developed by Berkeley from ATT's 6th edition of Unix.

Then came in 1987 the still Unix-oide operating system, Minix, created by Andrew S. Tanenbaum for school use. The main weakness of this operating system was that part of the code could not be modified and redistributed. In addition Minix16bits is not very well suited to 32bits machines that are very popular for personal computers at the time. It is mainly because of the small flaws of Minix that Linus Torvalds decided to start his project which will become one of the most used cores in the world today. Fun little anecdote moreover Linux was compiled with GCC (GNU C Compiler) on Minix. It should be noted that initially Linux was only a terminal emulator that he used to access the Unix server of his university: he wanted to use, regardless of any operating system, functions of his computer that Minix did not take into account. The very first version of Linux (0.01) was under the personal license of Linus Torvalds, later for version 0.99 it was put under GPL, to become the core that we know now.

Overview of Linux

From now on the term Linux and Unix will not be used either to designate a kernel but the operating system running around it.

The Linux system is a multi-user and multi-tasking system. As an operating system, its main role is therefore to ensure different tasks and users a good distribution of computer resources (memory, processor (s), disk space, printer (s), utility programs ...) without user intervention; it fully supports these users and when the requests are too important to be satisfied quickly, the user feels it by a certain slowing down (which can be really important, even unbearable ...), but the system (in principle) does not do not hang.

Linux is also a development system and users have at their disposal a very large number of tools, mostly simple to use, allowing them to write, edit and document their programs (publishers, compilers, debuggers, text processing system ...). Users have at their disposal a well-stocked toolbox, the main problem for them is to know what exactly it contains and what is the purpose of each of these tools!

In summary, we can say that the system is composed of:

• a kernel providing low-level memory and I / O management and sequencing of different tasks;
• one (or more) command language interpreter (s); there are indeed different Shell command languages, the most famous being the Bourne Shell (named after its author), another being the C-Shell developed at the University of Berkeley and the most common currently being the Bash. We will see in this tutorial a course of Bourne Shell and Bash. It is important to note that, whatever the version of the command language used, it is a real programming language with instructions and especially very powerful control structures;
• a fairly complete messaging system (mail, real-time conversation, logbook);
• a large number of utility programs including obviously a C language compiler, editors, word processing tools, communication software with other Linux systems (or other), generators of lexical and syntactic parsers ...

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