????????????????? Third class Linux Overview Linux generally has four main parts: kernel, shell, file structure, and utility. • Linux kernel? The kernel is the heart of the system, which is a core program that runs the program and manages hardware devices such as disk and printer. It accepts commands there and delivers the command to the kernel. 2. Linux shell? Shell is a user interface of the system, providing a user with the user with the kernel. It receives the command input command and feed it into the kernel. In fact, shell is a command interpreter that explains the command entered by the user and sent them to the kernel. Not only that, but shell has its own programming language for editing of the command, which allows users to write programs consisting of shell commands. The shell programming language has a lot of characteristics of normal programming languages, such as the loop structure and branch control structure, etc., the shell program written in this programming language has the same effect as other applications. Linux provides a visual command input interface (GUI) like Microsoft Windows. It provides a lot of window manager, which is like Windows, with windows, icons, and menus, all management through mouse control. Nowadays, the popular window manager is KDE and GNOME. Users of each Linux system can have his own user interface or shell to meet their own special shell needs. Like Linux itself, SHELL also has a variety of different versions. There are currently the following versions of the shell:? Bourne Shell: It is a Bell Lab. ? Bash: It is the Bourne Again Shell of the GNU, which is the default shell on the GNU operating system. Korn shell: It is the development of Bourne Shell and is compatible with Bourne Shell on most of the content. ? C shell: is the BSD version of Sun's shell. ????? 3. Linux file structure file structure is an organizational method on storage devices such as disk. Mainly reflected in the organization of documents and catalogs. The directory provides a convenient and effective way to manage files. We can switch from a directory to another, and you can set the permissions of the directory and files, set the share of the file. Using Linux, the user can set the directory and file permission to allow or reject other people to access it. The Linux directory features a multi-stage tree structure, and Figure 1.1 shows this tree level structure. Users can browse the entire system, you can enter any directory where you have authorized enters, access the files there. The interrelationship of the file structure makes shared data easy, and several users can access the same file. Linux is a multi-user system that stores the operating system itself in a dedicated directory starting with the root directory, sometimes specified as the system directory. The directory in the root directory in Figure 1.1 is the system directory. The kernel, shell and file structure form a basic operating system structure. They allow users to run programs, manage files, and use systems. In addition, the Linux operating system also has many programs called utility, and secondary users complete some specific tasks. ? 4. Linux utility standard Linux system has a set of programs called utility, which are special programs, such as ??????? editor, execution standard calculation operation, etc. Users can also produce their own tools. Practical tools can be divided into three categories: editor: used to edit files. Filter: Used to receive data and filter data. Interactive: Allows users to send messages or receive information from other users. The editor of Linux has: ED, EX, VI, and Emacs. ED and EX are line editors, VI and Emacs are full screen editors.
• Linux filter (Filter) reads, checks, and processing data from user files or elsewhere, and then outputs the result. In this sense, they filtered through their data. Linux has different types of filters, and some filter is used to edit commands to output an edited file. Other filters are looking for files by pattern and output partial data in this mode. There are also some execution word processing operations, detect formats in a file, output a formatted file. The filter of the filter can be a file, or the user typed from the keyboard, and can also be the output of another filter. The filter can be connected to each other, so the output of a filter may be an input to another filter. In some cases, users can write their own filter programs. The interactive program is the user's information interface with the machine. Linux is a multi-user system that must keep in touch with all users. Information can be sent and received by different users on the system. There are two ways to send information, one way is to dialogue with other users one-to-one link, and the other is a user to communicate multiple users at the same time, that is, the so-called broadcast communication. ???? The fourth lesson Linux's development Linux is an operating system designed for a personal computer. It was the first designed by Linus Torvalds. At that time, Linux was a personal research project in his purpose to design a more effective UNIX PC version for Minix users. Linus Torvalds call it Linux. MINIX is developed by Professor Andrew Tannebaum, published on the Internet, and is used by students around the world. Minix has more Unix features, but is incompletely compatible with Unix, Linus intends to design a more complete UNIX PC version for minix users, issued Linux 0.11 version in 1991, and released it on the Internet, free to use people . In the next few years, other Linux enthusiasts use their own usage, the existing UNIX standards and the features of the application, modification and add some content, making Linux more perfect. Linux designs interfaces with all major window managers, providing a large number of Internet tools such as FTP, TELNET, and SLIP. Linux provides a relatively complete program development tool, the most commonly used C compiler, and debugger. Although Linux has all the features and features of UNIX, it is the smallest, stable and fastest operating system. Under the minimum configuration, it can run on only 4MB of memory. Linux is developed in the Internet Open environment, which is constantly perfect by programmers around the world, and free for users. Despite this, it still follows the standard of commercial UNIX version, because in decades, UNIX version has appeared in a large number, and the Electronic Engineering Association (IEEE) has developed an independent UNIX standard, which is called a computer environment. Portable operating system interface (PSoix). This standard defines how UNIX systems operates, and the system call has also been specifically discussed. PSOIX limits all UNIX versions must rely on mass standards. The existing general Unix and popular versions are followed by POSIX standards, while Linux follows the POSIX standard from the beginning.
