How to use Linux screen command

1. Introduction to screen command

Screen is a full-screen window manager that allows multiple processes (usually interactive shells) to be multiplexed between physical terminals. Each virtual terminal has DEC VT100 terminal and ANSI X3 control functions. ISO 6429 (64) and ISO 2022 standards (e.g. insertion/deletion of lines and support for multiple character sets). Users can take advantage of each virtual terminal's scrollback history buffer and copy-paste mechanism to move text areas between windows. When screen is called, it creates a window containing the shell (or the specified command) and then gets out of your way so that you can use the program normally. You can then at any time create new (full-screen) windows containing other programs (including more shells), close the current window, view the list of active windows, turn the output log on and off, copy text between windows, view the scroll history, Switch between windows, etc. All windows run their programs completely independently. Programs continue to run when the window is not currently visible, and even when the entire screen session is detached from the user's terminal.

2. Usage examples

1. Install screen command

[root@s145]~# yum install -y screen
Installed:
screen.x86_64 0:4.1.0-0.27.20120314git3c2946.el7_9
Complete!

2. List all current sessions

[root@s145] ~# screen -ls
No Sockets found in /var/run/screen/S-root.

3. Create a new window

[root @s145]~# screen -S test
…
[root@s145]~# screen -ls
There is a screen on:
2877.test (Attached)
1 Socket in /var/run/screen/S-root.
[root@s145]~

#4. Exit the current window

  You can use ctrl a , and then enter d to exit the current window. You can also use screen -d to exit the current window. If you want to end only the window use exit.

5. Reconnect the window

  Use screen -r id or name to reconnect the session, The session status is required to be Detached before reconnecting the session.

6. Clear the dead status window

When the session window is ended After that, the process status becomes dead and unable to connect. At this time, you can use the command "screen -wipe" to clear the session window.

7. Session locking and unlocking

Enter ctl a s to lock the session. After locking, the screen will not respond to any input. After entering ctl a q, it will unlock. Although When the screen is locked, it will not respond but will accept the commands entered. After unlocking, all commands will be executed. Do not enter dangerous commands, so it is recommended to use ctl a x to lock.

Enter ctl a x to lock the session. You need to enter the user password before you can unlock it.

8. Session sharing

9. Send commands to the screen window

[root@s145]~# date && screen -S test -X screen ls > /tmp/1.txt
Tue Jan 11 17:12:24 CST 2022
[root@ s145]~# screen -S test -X screen sh /root/test.sh

10. Screen split screen

It’s normal to use shortcut keys to split the screen, but you can’t enter commands when the screen is split. If you know, you can leave a message and tell me the reason. Please give me some advice. Thank you!

11. Practical example

Write a script that continuously outputs

[root@s145]~# cat test.sh 
#!/bin/bash
\
while true
do
  echo "输出`date +%F-%T`"
  sleep 10
done

Create a screen window

[root@s145]~# screen -S echotest

Execute the test.sh script

Make the echotest window offline in other sessions

[root@s145]~# screen -d echotest
[3405.echotest detached.]

Usage: screen [-opts] [cmd [args]]

or ：screen -r [host.tty]

Ctrl a c: Create window
Ctrl a w ：Window list
Ctrl a n ：Next window

• ##Ctrl a p ：Previous window

• Ctrl a 0-9: Switch between the 0th window and the 9th window

• Ctrl a K (uppercase): Close the current window, and Switch to the next window (when exiting the last window, the terminal automatically terminates and returns to the original shell state)

• exit: Close the current window and switch to the next window ( When exiting the last window, the terminal automatically terminates and returns to the original shell state)

• Ctrl a d: Exit the current terminal and return to the shell command state before loading the screen

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