Linux run level is specified, help command

Run Level Description: 
0: Off
 1 : Single User [recover lost password]
 2 : Multi-user state [No network services]
 3 : Multi User Status [with internet services]
 4 : Reserved Level
 5 : GUI
 6: a system reboot

A, designated run level

1. Modify the default run level

vim / etc / inittab 

modify the last line: 
the above mentioned id: 5: initdefault:

2. Switch to run level

1. Basic Instructions

the init [0123456]       #init restart. 6

2. interview questions

How to find the root password, if we are not careful, forget the root password, how to get back.

Ideas: into single-user mode, and then modify the root password. Because the single-user mode, root can log in without a password.

Hands: 
Power -> press enter key at boot -> see an interface input E -> see a new interface, the second row (edit the kernel) is selected in the input e-> In the last input line 1, and then eNTER to -> again input b, then it will enter the single-user mode. 
At this time, we enter into single-user mode, use the passwd command to change the root password.

 Second, help command

man commands and configuration files 
help shell built-in commands 
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