system v init run levels systemd target name role
0 runleve10.target, poweroff.target shutdown
1 runleve11.target, rescue.target single-user mode
2 runleve12.target, multi-user.target equivalent to level 3
3 runleve13.target, multi-user.target multi-user text interface
4 runleve14.target, multi-user.target equivalent to level 3
5 runleve15.target, graphical.target multi-user graphical interface
6 runleve16.target, reboot.target restart
emergency emergency. target 紧急shell
The specific meaning of the parameters
Command: tell the Linux operating system what to do
Options: Tell command mode operation. Select the part is "_" character begins
Parameters: What is the impact description of the command
who: lists the current system in which users work
who: Shows all currently logged in user and the current date and time
date: displays the current date and time
Set date Time format: Month Day Year Time Division
hwclock-s Hardware Synchronization - System Synchronization
clear: Clear command ctrl-1 shortcuts
exit: exit