1. Common Linux distro What? And describe the connections and differences between different releases
A: The current market popular version has three schools, slackware, debian, redhat
1） 联系：三大流派的发行版都是通过linux内核源代码开发，以及Linux的应用程序都可以自由获得，所以许多公司建立自己的团队，开发出属于自己的linux发行版。
2） 区别：a.软件包命令不同，软件命名的方式不同；b.搜索库的方式不同；c.启动系统服务不同；d.开机启动项方式不同；e.网络配置方式不同2, print displays the current time, the format is: 20,181,209,211,008
DATE the Y +% m%% D% H% M% S 
. 3, to achieve automatic shutdown 20:30, and prompts the user
shutdown -h 20:30 AT 20:30 well be poweroff 
4, summarizes the history of management and command usage
history command: history and instructions executed commands for display. reads the command history command history file directory to history and the history command buffer directory command buffer write command file.
-c: Empty command history
-d offset: Delete history specifies that the first offset command
n: displays the most recent history of n
-a: append this session newly executed command history list to the history file
-r: Reading history file is attached to the history list
-w: save history list to the specified history file
-n: unread to read the history file line to the history list
-p: expand the historical parameters into multiple lines, but the history list does not exist
-s: expand history parameters in a row, appended to the history list
Quick repeat a command execution
use the arrow keys, and press Enter to execute.
And press Enter !! executed.
Enter! -1 and press Enter to execute.
Press Ctrl + P and press Enter to execute
5 summarizes Linux usage to help
1.whatis (see the first few chapters only) example: whatis cat only the first chapter has 
2.help (internal command help command) Examples: Help enable 
3.COMMAND --help (external commands help command), display usage summary and list of parameters, most used, but not all examples: DATE --help 
4.man (help command external commands), man pages stored in / usr / share / man, almost every command has a man of "page", man pages are grouped into different "chapters", collectively referred to as Linux manual. Examples: man 5 passwd (configuration file format) 
5.info, man commonly used in the Command Reference, info than the man command reference tool more detailed and more, GNU tool info way common document for reference, the organization of similar sites, there is no argument, It lists all the pages. * No later followed by a link. Examples: info DATE
. 
6. Get help through local document
System-> Help (centos6)
Applications -> documentation-> Help (centos7)
/ usr / report this content share / DOC / directory (to store the installation package corresponding document)
7. online documentation for help
8. Red Hat global support services