Linux Basic Knowledge points Miscellaneous note

I. Composition of computer systems

Computer systems can be broadly divided into two parts, consisting of hardware and software systems.

1.1. von Neumann System Overview

There is a person who contributes a lot to the computer, we must remember his name, called John von Neumann. He was a Hungarian-born American Jew who, during his time at Princeton, summed up the development of quantum mechanics in a mathematical sense, and published the mathematical basis of quantum mechanics, a book that was a work of literature. He has made outstanding contributions in the fields of physics, mathematics, and computers. His contribution in the field of computer is more significant, put forward to the computer's main structure principle-the principle of stored procedures, to determine the basic components of the computer consists of five major parts, namely, the operator, controller, memory, input and output devices.
The five basic parts of a computer:

• CPU (operator, controller), these two basic components from the CPU, wherein the operator is mainly on the data process of various arithmetic operations and logic operations, in short, is to process data processing. The controller is to explain the control information prescribed by the program, mainly according to the requirements to complete the control, program scheduling, data, address, coordinate the work of the computer and the memory and external equipment access and so on;
• Memory, mainly used to store programs, data and various signals, command information;
• Input (device), mainly used to complete the release instructions, provide data input. Inputting programs, raw data, text, characters, control commands, etc. into the computer;
• The output (device) is mainly used to output the results of processing after the processed data has been completed. The computer's intermediate results or the final results, the various data symbols in the machine and text or various control information and other content output and echoed.

1.2, the hardware system simple composition of the host itself

The host part can be simply divided into CPU (mainly by the operator and the controller two parts), memory (ROM and RAM), etc.

External devices

Common external devices have external memory (data hard disk, data floppy disk, data CD, data tape, etc.), input device (keyboard and mouse, etc.), output device (computer monitor, printer, etc.), other equipment;

1.3, software system simple composition

Software systems can be easily divided into system software and application software, the former mainly refers to our familiar operating system, the latter mainly refers to the third-party applications.

1.4, CPU production companies and the type of CPU common several production companies

INTEL,AMD,IBM These major manufacturers of the production of CPU is more common;

CPU Type

Common CPU types, the following is a list:
x86
x64
Arm
m68000 (commonly known as m68k)
Power
Powerpc
UltraSPARC
Alpha
Itanium
such as

1.5, the concept of the operating system

The operating system is a computer program that manages and controls computer hardware and software resources, and is the most basic system software that runs directly on "bare metal". The operating system provides an interface for the user to access the computer and provides an interface for the application to access the computer's hardware resources. It can implement the following basic functions:

• Hardware Drivers
• Process Management
• Memory management
• Network management
• Security management
• File Management
  Each of the above features is a relatively core embodiment, used to better complete the computer to provide external services.

The operating system can be easily divided into the following categories:
Operating systems for server classes
Operating systems for desktop classes
Operating systems for mobile classes

In order to realize the function management of the operating system, the operating system is divided into two levels, one is called user space, and the other is kernel space (Kernel spaces).

Second, the principle of program operation

We all know that the computer system is composed of hardware systems and software systems, to provide services, so in order to better access these so-called hardware resources, on the abstraction of an operating system model, to help users to block the access to the underlying hardware details, all the functions are integrated into the operating system. These implementations are what we call system calls. The system call hides the underlying interface to the hardware resource operation, which is universal and relatively low level. Because the system calls this layer interface for third-party application developers still have some difficulty, the function is more complex, so in the interface to provide system calls to implement a layer of interface, called Library. A library is an interface that combines system calls with complex functions, and users can invoke these interfaces (and sometimes make system calls directly) to accomplish some function development. We mentioned the concept of user space and kernel space, we need to switch between the two states, because the application is usually run in user space, and its registration using the underlying resources requires kernel space to allocate management, so we need to switch from the user state to the kernel state. It then switches from the kernel state to the user state.

In the principle of program operation, there are several core concepts to know. One is called the Application Binary interface (abi,application binary Interface) and the other is the application interface (Api,application programming Interface). The ABI describes the underlying interface between the application and the operating system, allowing the compiled target code to run without modification in a system with a compatible ABI. The API defines the interface between the source and the library, so the same source code can be compiled in any system that supports the API.

Third, mainstream Linux distribution and branch

Redhat Series:
RHEL (Redhat Enterprise Linux, Red Hat Business Edition);
CentOS (a community-maintained version of Rhel compatible, followed by Red Hat pacified);
Fedora Core: Developed from the previous desktop version of Red Hat;
Slackware Series:
Suse Linux Enterprise Server (Sles,suse Corporate Edition)
Opensuse:suse Desktop version

ArchLinux Series
Ubuntu series
Debian series

Here are three maps that can be easily referenced. Images from:
Photo source

• Red Hat Series
  

• Slackware Series
  

• Debian series
  

Iv. how Linux obtains Help documentation information and instructions 4.1, built-in commands and external commands

Built-in commands are part of the shell program, such as Cd,file

所有的内建命令：:,  .,  [, alias, bg, bind, break, builtin, caller, cd, command, compgen, complete, compopt, continue, declare,dirs, disown, echo, enable, eval, exec, exit, export, false, fc, fg, getopts, hash, help, history,  jobs,  kill,  let,local,  logout,  mapfile,  popd, printf, pushd, pwd, read, readonly, return, set, shift, shopt, source, suspend, test,times, trap, true, type, typeset, ulimit, umask, unalias, unset, wait

All of the above built-in commands must know the meaning, 90% can be easily used to qualify.

External command:
such as LS,IP,SS, etc.

• To see whether a command belongs to an external command or to a built-in command, see the case:

  [[email protected] ~]# type lsls is aliased to `ls --color=auto‘[[email protected] ~]# type ipip is /usr/sbin/ip[[email protected] ~]# type ssss is /usr/sbin/ss[[email protected] ~]# type cdcd is a shell builtin[[email protected] ~]# type [[ is a shell builtin[[email protected] ~]# whatis cdcd (1)               - bash built-in commands, see bash(1)[[email protected] ~]# whatis lsls (1)               - list directory contents

• How to view the help manuals for built-in commands and external commands

  内建命令用help来查询，例如：help cd或者通过man bash然后通过检索关键字的形式来搜索到我们要了解的内建命令的帮助信息。对于外部命令，我们使用man来查询其用法。

4. Manual on Man

• User manual Location

  /usr/share/man[[email protected] ~]# cd /usr/share/man/[[email protected] man]# lscs  de  fr  id  ja  man0p  man1p  man2   man3   man3x  man4x  man5x  man6x  man7x  man8x  man9x  pl  pt_BR  sk  tr     zh_TWda  es  hu  it  ko  man1   man1x  man2x  man3p  man4   man5   man6   man7   man8   man9   mann   pt  ru     sv  zh_CN

• Part of the Man Handbook

            SECTION:                NAME：功能性说明                SYNOPSIS：语法格式                DESCRIPTION：描述                OPTIONS：选项                EXAMPLES：使用示例                AUTHOR：作者                BUGS：报告程序bug的方式                SEE ALSO：参考            SYNOPSIS:                [] : 可选内容；                <> : 必须提供的内容；                a|b|c : 多选一；                ... : 同类内容可出现多个；

• Man Manual Chapter

Chapter Name	Chapter meaning Introduction
Man1	User commands
Man2	System calls
Man3	C Library Call
Man4	Device files and special files
Man5	File format (configuration file format)
Man6	Bring your own puzzle games to use Help
Man7	Miscellaneous Help
Man8	Help for management tools and daemon classes

How do I use the Man Handbook in chapters?
Man number command

• Use shortcut keys in Man Handbook

  翻屏： 空格键：向文件尾部翻一屏；b：向文件首部翻一屏；Ctrl+d：向文件尾部翻半屏；Ctrl+u：向文件首部翻半屏；回车键：向文件尾部翻一行；k：向文件首部翻一行；G：跳转至最后一行；#G：跳转至指定行，#是一个数字；1G：跳转至文件首部；文本搜索：        /keyword : 从文件首部向文件尾部依次查找；不区分字符大小写；        ?keyword : 从文件尾部向文件首部依次查找；        n：与查找命令方向相同；        N：与查找命令方向相反；退出：     q：quit

Linux Basic Knowledge points Miscellaneous note