File view command

cat

1. Used to view file data

cat a.txt

2. Merge files

cat a.txt b.txt > c.txt

3. Write data to file

cat > d.txt 

There is one thing to pay attention to when writing data in this way ：cat > d.txt When entering data , Will be will be d.txt Empty data in .

cat >> d.txt

Enter data at the end of the file ,ctrl+d End input

 “>>” Move the cursor to the end of the file , Then write data （ The original data will not be lost ）

more

When the contents of the file are not displayed on the screen , You can use more command , Split screen content .

more filename

You can use spaces （ There are many contents in one jump ） Or return （ Look down a little ） Look down at the contents of the file , I don't want to check , Can pass q immediate withdrawal .

You can view the system through the red hat key .

less

less And more be similar , There is only one difference .

less And more The difference between ：

less The displayed file content will not be left in the terminal interface

less The contents of the displayed file , There is no percentage in the lower left corner

less The contents of the displayed file You can use the arrow keys to view （more You can only go down ）

head

Before displaying the file n That's ok , Default 10 That's ok

head -n filename

tail

After displaying the file n That's ok , Default 10 That's ok

tail -n filename

  Used to view log files

tail This command is often used to view log files , Because log files generally only view recently generated log data , That is, look at the end of the log file

tail -f filename(-f follow Real time tracking display End of file information , Dynamic tracking )

  

User management command

Storage of basic user information

user name , User password , group information , user ID, Description of the user , The address of the terminal

Storage location /etc/passwd

user name	password	UID	GID	Description information	Home directory	command interpreter
root	x（ It means there's a code ）	user ID	Group ID	A brief description of the user	It's usually a home directory	Default command interpretation

  For the sake of safety , After all user passwords are encrypted separately , Save in a file （/etc/shadow）, This file can only root see

user name $ encryption algorithm ID$ secret key $ Ciphertext

Add new user

useradd  user_name( A new user name )

When creating users , Generally speaking, a home directory with the same name will be created , Put it in /home Under

Red hat will create a home directory with the same name when creating a new user
uburtu Home day records will not be automatically added , We need to manually add , Or want to add home directory automatically , New users can be added through the graphical interface

Change Password

adopt passwd This command changes the password ：

passwd user_name（ Change user password ）

You can switch between super users , Forcibly modify various passwords sudo passwd user_name

Delete user

userdel  Delete user

Be careful ：

1. The deleted user is not logged in

2.userdel After deleting users , The deleted user's home directory still exists

3.userdel -r user_name Deleting a user will also delete the home directory