A. Start, shutdown, login, log out related commands
<login> Login
<logout> Log Out
<exit> Log Out
<shutdown> Stop System
<reboot> reboot
<poweroff> Power off
<sync> write the contents of memory to disk
<lilo> Install Lilo startup management Program
<grub> Install Lilo startup management Program
Two. Shell-related commands
<chsh> Switch Shell
<alias> set Command alias
<unalias> Cancel Command Alias
<which> Show where the command is located
<type> Query Command type
<echo> display string or variable contents
<set> set/Show Shell variables
<printenv> Display Environment variables
<export> Setting Environment variables
<env> Setting TEMP Environment variables
<unset> Releasing environment variables
<setenv> Setting Environment variables
<unsetenv> Releasing environment variables
<source> implementation of the order in the document
<man> Search Command Manual
<info> Query Hypertext Command Manual
Introduction to <whatis> Display commands
<apropos> Search Manual by keyword
Three. User Management related commands
<su> Switch to another user
<useradd> Additional users
<adduser> Additional users
<userdel> Delete Users
<usermod> Modify user Settings
<chfn> Modify user's personal information
<groupadd> Append Group
<groupdel> Delete Group
<groupmod> Modify Group settings