Screen manager

screen is a command-line program that we can use to open multiple virtual terminals ("windows") inside the same session. Processes that we started running in screen will continue to run when their window is not visible, and even if we get disconnected! This comes very handily when we are working via ssh on remote machines.

Imagine that we have to run a program that would require 3 full days to complete the task. If we would run it without screen session this would require us to stay online logged-in for the entire time that the program needs to complete its task. Instead, we can create a screen session from which we can log out at any time and later on switch off our local machines, and come back later to the same screen session in 3 days or whenever we want to.

Also, imagine that you would like to open a few tabs when you are logged-in on the remote machine. Whenever you try that you will be redirected to your local machine terminal and you would have to log in again and to move yourself to the desired location in the file system. This can be boring and time-consuming and screen can save us some time there too! We can have multiple "windows" within our screen session, and whenever we open a new "window" we will continue from the same place where we opened our session.

Starting screen session

To start named screen session with name my_first_screen_session type:

screen -S my_first_screen_session

P.S. you can also start an unnamed session by just typing screen but we recommend you to name your sessions.

Screen commands

When within the screen session we can perform tasks that we would do on a normal terminal (e.g. running programs, doing ls, changing directories or what every you have to do) but also we can direct our commands to the screen program itself (e.g. we can tell screento move from one to another window, or close screen session, rename and many others).

By pressing Ctrl+a (i.e. while holding down the Ctrl key type the letter a) we will redirects our commands to the screen program itself and commands that follow Ctrl+a will determine the action that screen program will perform.

Below are some of the most frequently used screen commands. Please note that here we are referring to a as a symbol for pressing "Taster "A" (i.e. a = A), while with A we refer to an action of pressing "Taster A" together with "Shift" (i.e. A = A+Shift):

Detaching from screen session

We can detach from the screen session at any time by typing: Ctrl+a and d After we detach from the screen session all the program running in the screen session will continue to run.

Renaming screen session

To rename an existing session open it first, and once inside the session press Ctrl+a then type :sessionname my_session_name and press Enter.

Resuming and listing running screen sessions

To resume screen session use the following command:

screen -r

In case you have multiple screen sessions running on your machine, you will need to append the screen session name after the -r option.

We can list the current running screen sessions with:

screen -ls

There are screens on:
        30285.amazing_whales    (04/17/2020 07:19:10 AM)        (Detached)
        30275.love_whales       (04/16/2020 09:28:50 AM)        (Detached)
        28591.pts-0.evop-login  (04/14/2020 08:04:53 AM)        (Detached)
3 Sockets in /run/screen/S-vladimir_bajic.

If we would like to resume screen called 30275.love_whales, then we would type:

screen -r love_whales

Quitting screen sessions

When in screen session we can quit it (i.e. kill all windows and terminate screen) with this command: Ctrl+a \ or Ctrl+a then type :quit

When deatached from screen session we can quit it:

screen -X -S my_first_screen_session quit

Getting help

When in screen session type Ctrl+a and ?. This will show us commands or parameters on screen.

When outside screen you can check for the manual page of screen command by typing: man screen, or you can check the help page of screen command with screen --help.