Today we talk about screen: a small utility command line for Linux systems.

Screen, quite simply, he's able to multiply the terminals at our disposal, of undock a terminal by its process and maintain active process in the background (by returning the terminal to use).

Screen is particularly useful when it launches a command that requires a response time rather long (such as a backup) be it launched locally or on a remote server. The timeout of the server or the user accidentally kill could lead to an interruption command and frustrate the time spent.

But let's see how it works:

screen	start screen and returns the shell
screen + comando	start the program “command” inside “screen”
Once started “screen“
“ctrl+a” and then “c“	creates a new terminal
“ctrl+a” and then “n“	skips to the next terminal
“ctrl+a” and then “p“	switches to the previous terminal
“ctrl+a” and then “d“	“unhooks” screen from the session

Once unhooked from the session can end the SSH tunneling or close the terminal. The program will continue to run in the background.

To retrieve a previous session will take “hang up”:

screen -list	lists all the started sessions
screen -r	retrieves a previously started session

Below is one example of the terminal with two sessions “dropped” The screen.

~$ screen -d
There are screens on:
16268.pts-3.joe-desktop (01/12/2019 20:58:09) (Detached)
23799.pts-4.joe-desktop (01/12/2019 16:30:08) (Detached)
There is no screen to be detached.
~$

To “hang up” to a specific session just specify the PID. I our case “screen -r 16268“.

To clear a screen that is the command: screen -X -S {PID della sessione} kill.