In-depth analysis of the structure and features of Linux

Article Title: in-depth analysis of the structure and features of Linux. Linux is a technology channel of the IT lab in China. Includes basic categories such as desktop applications, Linux system management, kernel research, embedded systems, and open source.
　　 1. Linux Kernel
The kernel is the heart of the system and the core program for running programs and managing hardware devices such as disks and printers. It receives commands from the user and sends them to the kernel for execution.
　　
　　 2. Linux Shell
Shell is a system user interface that provides an interface for users to interact with the kernel. It receives user-input commands and sends them to the kernel for execution.
　　
In fact, Shell is a command interpreter that explains the commands entered by the user and sends them to the kernel. In addition, Shell has its own programming language for editing commands. It allows users to write programs composed of shell commands. The Shell programming language has many features of a common programming language, such as its loop structure and branch control structure. The Shell program written in this programming language has the same effect as other applications.
　　
Linux provides a visual command input interface like Microsoft Windows-the graphical user interface (GUI) of X Window ). It provides a lot of Window managers, and its operations are like Windows. There are Windows, icons and menus, and all management is controlled by the mouse. Currently, KDE and GNOME are popular Window managers.
　　
Each Linux user can have his/her own user interface or Shell to meet their own dedicated Shell needs.
　　
Like Linux, Shell has many different versions. The following versions of Shell: Bourne Shell: Developed by Bell Labs.
BASH: it is the GNU Bourne Again Shell, which is the default shell on the GNU operating system.
Korn Shell: it is the development of the Bourne SHell and is compatible with the Bourne Shell in most aspects. C Shell: the BSD version of SUN Shell.
　　
　　 3. Linux File structure
The file structure is the method of organizing files stored on disks and other storage devices. It is mainly reflected in the organization of files and directories. Directory provides a convenient and effective way to manage files. We can switch from one directory to another, and set the Directory and file permissions to set the degree of file sharing.
　　
In Linux, you can set the Directory and file permissions to allow or deny access to other users. The Linux directory adopts a multi-level tree structure, and. 1 indicates this tree hierarchy. You can browse the entire system and access any authorized directory to access the files.
　　
The Association of file structures makes it easy to share data. Several users can access the same file. Linux is a multi-user system. The resident program of the operating system is stored in a dedicated directory starting from the root directory, and is sometimes specified as a system directory .. The directory under the root directory in 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 the system. In addition, the Linux operating system also has many programs called utilities to help users complete specific tasks.
　　
　　 4. Linux utilities
Standard Linux systems have a set of programs called utility tools. They are specialized programs, such as editors and standard computing operations. You can also generate your own tools.
There are three types of utility:
Editor: used to edit files.
Filter: used to receive and filter data.
Interactive Program: allows users to send information or receive information from other users.
Linux editors include: Ed, Ex, Vi, and Emacs. Ed and Ex are row editors, and Vi and Emacs are full screen editors.
　　
Linux filters read input from user files or other places, check and process data, and then output results. In this sense, they filter the data that passes through them. Linux has different types of filters. Some Filters use the line editing command to output an edited file. In addition, some filters are used to search for files by mode and output part of the data in this mode. Some other operations are performed to check the format of a file and Output A formatted file. The input of the filter can be a file, data typed by the user on the keyboard, or output of another filter. Filters can be connected to each other. Therefore, the output of one filter may be the input of another filter. In some cases, you can write your own filter program.
　　
An interactive program is the information interface between the user and the machine. Linux is a multi-user system that must be in touch with all users. Information can be sent or received by different users on the system. There are two ways to send information: one is to communicate with other users through one-to-one links, and the other is to communicate with multiple users at the same time, that is, broadcast communication.
　　
The Linux operating system has developed rapidly in just a few years, which is inseparable from the good features of Linux. Linux contains all Unix functions and features. To put it simply, Linux has the following main features:
　　
1. Openness
　　
Openness means that the system complies with world standards, especially the OSI International Standards. All hardware and software developed in compliance with international standards are compatible with each other and can be easily interconnected.
　　
2 users
　　
Multi-User means that system resources can be used by different users, that is, each user has specific permissions on their own resources (such as files and devices), without affecting each other. Both Linux and Unix have the characteristics of multiple users.
　　
3. Multi-task
　　
Multi-task is a major feature of modern computers. It means that the computer executes multiple programs at the same time, and each program runs independently of each other. In Linux, every process is scheduled to access the microprocessor equally. Because the CPU processing speed is very fast, the result is that the started application seems to be running in parallel. In fact, there is only a short delay between the processor executing a group of commands in an application and the Linux scheduling microprocessor running this program again, which is invisible to users.
　　
4. Good user interface
　　
Linux provides users with two interfaces: user interface and system call. The traditional Linux user interface is a text-based command line interface (shell), which can be used both online and offline. Shell has strong programming capabilities, allowing users to easily use it to program, thus providing users with more advanced means to expand system functions. A Programmable Shell combines multiple commands to form a Shell program, which can be run independently or simultaneously with other programs.
　　
The system calls the interface used for programming. Users can directly use the System Call commands provided by the system during programming. The system provides low-level and efficient services for user programs through this interface.
　　
Linux also provides a graphical user interface. It uses the mouse, menu, window, scroll bar and other facilities to present a user with an intuitive, easy to operate, interactive and friendly graphical interface.
　　
5 device independence
　　
Device independence means that the operating system treats all external devices as files. Any user can manipulate and use these devices as long as their drivers are installed, you don't have to know their specific forms of existence.
　　
An operating system with device independence simplifies the process of adding new devices by treating each peripheral device as an independent file. When a new device needs to be added, the system administrator adds the necessary connections to the kernel. This connection, also known as a device driver, ensures that the kernel processes the device in the same way each time it calls the device to provide services. When new and better peripherals are developed and delivered to users, operations allow immediate access to these devices without restrictions after they are connected to the kernel. The key to device independence lies in kernel adaptability. Other operating systems only allow a certain number of external devices or some types of external devices to connect. The device-independent operating system can accommodate any type and any number of devices, because each device is accessed independently through its dedicated connection to the kernel.
　　
Linux is an operating system with device independence. Its kernel is highly adaptive. As more programmers join Linux programming, more hardware devices are added to various Linux kernels and release versions. In addition, because you can get the Linux kernel source code for free, you can modify the kernel source code to adapt to the new external devices.
　　
6. Rich network functions
　　
A complete built-in network is a major feature of Linux. Linux is superior to other operating systems in terms of communication and network functions. Other operating systems do not have the ability to connect networks so closely integrated with the kernel, nor have the flexibility to build in these networking features. Linux provides users with comprehensive and powerful network functions.
　　
Internet is one of its network functions. Linux provides a lot of software that supports the Internet for free. The Internet is established and prosperous in the Unix field. In this regard, Linux is quite convenient to use, users can use Linux to communicate with others in the world over the Internet.
　　
File Transfer is the second of its network function. You can use some Linux commands to transmit internal information or files.
　　
Remote access is the third of its network functions. Linux not only allows file and program transmission, but also provides system administrators and technicians with windows to access other systems. With this remote access feature, a technician can effectively serve multiple systems, even if those systems are located far apart.
　　
7. Reliable System Security
　　
Linux has adopted many security technical measures, including Read and Write Permission control, protected subsystems, audit tracking, and core authorization, this provides the necessary security protection for users in multiple network environments.
　　
8. Good portability
　　
Portability refers to the ability to move an operating system from one platform to another so that it can still run in its own way.
　　
Linux is a portable operating system that can run in any environment from a microcomputer to a large computer and on any platform. Portability provides a means for different computer platforms running Linux to communicate accurately and effectively with any other machine without additional special and expensive communication interfaces.
(In the next lesson, I will work with you to learn how to install
The Linux operating system has developed rapidly in just a few years, which is inseparable from the good features of Linux. Linux contains all Unix functions and features. To put it simply, Linux has the following main features:
　　
1. Openness
　　
Openness means that the system complies with world standards, especially the OSI International Standards. All hardware and software developed in compliance with international standards are compatible with each other and can be easily interconnected.
　　
2 users
　　
Multi-User means that system resources can be used by different users, that is, each user has specific permissions on their own resources (such as files and devices), without affecting each other. Both Linux and Unix have the characteristics of multiple users.
　　
3. Multi-task
　　
Multi-task is a major feature of modern computers. It means that the computer executes multiple programs at the same time, and each program runs independently of each other. Scheduling of each