Linux system get command Help method and simple command introduction

Commands in a Linux system are generally divided into two types: internal commands and external commands

1. Internal command: Internal command, also known as built-in command, when the system starts to call into memory, is resident memory, so the implementation of high efficiency.

2. External command: The external command is the software function of the system and is read into memory from the hard disk when the user needs it.

Methods for distinguishing internal and external commands: type command
~]# type COMMAND
If the search results appear as "inline" or "Buildin", the internal command will be the result of the external command;

How to get help for internal commands: Helper command
~]# Help COMMAND

There are several ways to get help for external commands:

1.man command: Help manual for external commands;
Man Nine chapters:
1. User commands (commands that all users can execute)
2. System calls
3.C Library Call
4. Equipment and special documents
5. Configuration file format
6. Game-related Help information
7. Miscellaneous
8. System Management Class commands
9. Kernel-related Help information

Some of the fields commonly seen in the Man Handbook are:
Name: A simple description of the program names and related functions;
Synopsis: The syntax format used by the command;
DESCRIPTION: Detailed description information of the program;
Options: A detailed description of the use of the option and the meaning of the option;
AUTHOR: Information for program authors
EXAMPLES: Examples of the use of command programs;
REPORTING BUGS: The way in which bugs are included in the reporting program, usually e-mail;
See ALSO: Additional reference content
File: Other documentation related to the program, such as configuration files, readme documents, etc.;

The meaning of some special symbols that may appear in the Help information:
[]: Can omit do not write, also can choose to use according to need;
{}: A vertical bar "|" is generally included in curly braces, which means that all items must be selected and only one used; having or meaning;
<>: The content that must be written;
... : can have more content;

eg:~]# man COMMAND

2. Use the Whereis command to get help;
Can view the program's binaries, source code files and the location of the Help manual;

3.whatis command
You can get the description information of the manual page of the command that is matched to;

4.which command
You can display the way the alias of the command is defined and the path to the binary file of the command;

5.info command
~]# Info COMMAND
Get the online Help documentation for the command;


Simple commands for the System Management class:
Logout: Log Out
Exit, Logout
Reboot (reboot): Shut down all processes running in memory, turn off system kernel, power cycle all computer parts, load kernel, launch application, print login prompt;
Reboot,shutdown-r {# | now | time} (recommended), INIT6

#: A number that represents a relative time, that is, a reboot after the # minute;
Now: Reboot immediately, equivalent to 0;

Shut down the system (shut down): shuts down all processes running in memory, shuts down the system core, and loses power to all computer components.
halt,poweroff,init0,shutdown-h {# | now | time} (recommended)

Linux system get command Help method and simple command introduction