Basic Linux Knowledge

first, the computer system     

Computer system consists of two parts: hardware (Hardware) system and Software (software) system.

The composition of the hardware system is divided into five main parts:

1. Controller: is the central nervous system of the whole computer, its function is to explain the control information prescribed by the program, control according to its requirements, dispatching program, data, address, coordinate the work of each part of the computer and access to memory and peripherals.

2. Datapath: The function of the operator is to perform various arithmetic and logical operations on the data, i.e. processing the data.

3. Memory: Memory function is to store programs, data and various signals, commands and other information, and when necessary to provide this information.

4. Input system: Input device is an important part of the computer, the input device and output device is called external device, referred to as peripheral, the function of the input device is to the program, raw data, text, characters, control commands or data collected in the field of information input to the computer. Common input devices are keyboard, mouse, photoelectric input machine, tape drive, disk drive, CD-ROM machine and so on.

5. Output system: The output device and the input device is also an important part of the computer, it put out the intermediate results or the final result of the machine, various data symbols and text or a variety of control signals and other information output. The output devices commonly used by microcomputer are display terminal CRT, printer, laser printing machine, plotter and tape, CD-ROM machine and so on.

The composition of the software system is mainly divided into two parts:

system software refers to the control and coordination of computer and external equipment, support application software development and operation of the system, is a collection of programs without user intervention, the main function is to dispatch, monitor and maintain computer systems, responsible for the management of computer systems of various independent hardware, so that they can coordinate work. System software allows computer users and other software to treat computers as a whole without having to take into account how each of the underlying hardware works. (such as Windows, Linux, Dos, UNIX and other operating systems are part of the system software.) ）

Application software (application software) is a variety of programming languages that users can use, as well as a collection of applications compiled in various programming languages, which are divided into application packages and user programs. An application package is a collection of programs designed to solve certain types of problems with a computer for use by multiple users. Computer software is divided into two major categories: System software and application software. Application software is a part of the software to meet the needs of users in different areas, different issues and applications. It can widen the application field of computer system, enlarge the function of hardware. (such as word, Excel, QQ, etc. belong to the application software)

Second, the server

Servers server is a computer that is a high-performance computer that provides a variety of services to client computers in the network.

The server under the control of the network operating system, will be connected with the hard disk, tape, printer and expensive dedicated communications equipment to the network to share customer sites, but also for network users to provide centralized computing, information dissemination and data management services.

Server By application function can be divided into:

Web server, database server, mail server, file server, middleware application server, log server, monitoring server, program version control server, virtual machine server, print server, domain control server, multimedia server, Communication Server, ERP server, etc.

Servers are categorized by form factor:

Tower servers, rack servers, blade servers.

Third, the Linux operating system

1, the philosophical Thinking of Linux:

① All documents: organize almost all resources, including hardware devices, into file formats.

② consists of a number of single-purpose small programs: A program that only implements one function , and does it well.

③ combines small programs to complete complex tasks.

④ try to avoid interacting with the user: Goal: Implement scripting to automate certain functions.

⑤ to save configuration information using plain text files: Objective: A shared text editor is able to complete the system configuration work.

2. Getting Started with Linux:

1. Root User:

A special administrative account is also known as Superuser, Root is close to complete system control, has almost unlimited ability to damage the system, and unless necessary, do not log on as root.

Ordinary (non-privileged) users:

Limited authority, the ability to cause damage is relatively limited.

Command-line prompt:

[[Email protected]~]#

[[Email protected]~]$

Root indicates the current logged on user, localhost indicates the hostname, ~ represents the current directory, #表示超级用户, $ represents a normal (non-privileged) user.

2. Terminal Terminal

Server non-essential parts

User interaction with the host, the device must be used

Physical Terminal: Direct access to the local display and keyboard equipment/dev/console

Virtual Terminal: The terminal which is attached to the physical terminal, which is implemented by virtual software, the device file path:/dev/tty#,centos 6 default boot 6 virtual terminal ctrl+alt+f#: [1,6]

Graphics Terminal: A virtual terminal, attached to the physical terminal on the virtual implementation of software-based terminal, but additional to provide desktop environment;

Analog Terminal: Open command line in GUI and remote Open interface based on SSH protocol or Telnet protocol, device file:/dev/pts/# [0,∞]

View current terminal devices: TTY

3. The difference between the currently used command is an internal or external command:

~]# type COMMAND

4. Command format:

COMMAND [OPTIONS ...] [ARGUMENTS ...]

Options: One or some of the features used to enable or disable commands;

Short options:-C, for example:-L,-H

Long options:--word, for example:--all,--human-readable

Parameters: The object of the command, such as file name, user name, etc.

Attention:

(1), multiple options, and multiple arguments and commands separated by white space characters

(2), Cancel and end command execution: ctrl+c,ctrl+d

(3), multiple commands can be used; separate symbols

(4), a command can be divided into multiple lines

5. date-Display Date and time

Two types of clocks for Linux:

System clock: Run by the Linux kernel through the CPU's operating frequency;

Hardware clock: Motherboard

Hwclock,clock: Display Hardware clock

~]# clock-s or ~]# clock--hctosys to calibrate the system clock, whichever is the hardware clock

~]# clock-w or ~]# clock--SYSTOHC to calibrate the hardware clock, whichever is the system clock

6. cal-Display Calendar

~]# cal Displays the current date

~]# Cal Month Year displays the specified date

7. Screen command:

Open the new screen:

Screen–s [SESSION]

Join session:

screen–x [SESSION]

Exit and close screen:

Exit

Peel the current screen:

Ctrl+a,d

Show all screens that are already open:

Screen-ls

Restore a screen

Screen-r [SESSION]

8. Echo command

Function: Display characters

Syntax: Echo [-nee][string]

Description: Echo will send the input string to standard output. The output string is separated by a white space character, and a newline number is added at the end

echo "$VAR _name": variable is replaced, double quotation mark table weak reference

Echo ' $VAR _name ': variable does not replace, strong reference

$echo –e "Enter the file name: \c"

Echo needs to print the escape character using the-e parameter.

echo Command options:

-N does not wrap characters at the end of the line

-E If the following character appears in the string, it is handled in particular, not as a general text output:

\a issued a warning sound;

\b Backspace key

\c finally not add the line break symbol;

\ n Wraps and the cursor moves to the beginning of the line;

\ r The cursor moves to the beginning of the line, but does not wrap;

\ t Insert tab;

\ \ insert \ character;

\0NNN insert ASCII character represented by NNN (octal)

Echo-e "\033[43;31mred color\033[0m"

\XHH Insert the ASCII character represented by the HH (hexadecimal)

This article from "Progress a little every day" blog, declined reprint!

Basic Linux Knowledge