Create user login:
We use the useradd command to complete!
For example, useradd chuan
specifies the password: passwd chuan
enters the password:
switch to the created user: su chuan
exits the current user with exit:
remember: if no group is specified for the user, the useradd command will create a group with the same name and put the user in Go in,
No password is required when using root user to operate other users, on the contrary, when switching between other users, you need to enter the set password! 
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History command:
In addition to basic usage to display the history of command execution, occasionally we need to know the specific time of command execution:
as follows:
To satisfy the usage, the operation is as follows:
vi .bash_profile 
Next, enter the vim edit box and perform the following operations: enter the compilation mode (insert) and press the letter i to enter it. After entering the configuration, press ESC + colon + to save and exit!
Specify the source of the profile and display it
Successfully execute the history view operation:
