What, Why and How of Linux Screen

What is screen?

Screen is a terminal multiplexer which helps you to start a screen session and open any number of windows inside the session.

Why do we need screen?

Sometimes, when we perform a long-running task on a remote machine and suddenly the connection lost or your client machine have problem, the SSH session will be terminated and all of your work is GONE.

It happend many times especially in training a Machine Learning/ Deep Learning models because sessions are dependent on your client machine. Fortunately, we can eliminate the problem by using a utility called screen

How to use screen?

1. Install screen for Ubuntu

sudo apt-get install screen

2. Run Screen for the first time

screen

Now, you can run a long-running task like training a Deep Learning models, download very heavy files without worrying about the connection lost .

To detach an attached screen : screen -d

Press CTR-A then press d to detach but preserve the screen, you can re-attach later.

3. Re-attach the Terminal session

screen -r This command will re-attach to your current running session if you just have 1 screen session. In case of you have more than 1 screen session, you can use the command below to see all sessions: screen -ls

The results will be like:

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1(base) medic01@u20:/data1/kynd$ screen -ls
2There is a screen on:
3        3350892.pts-9.u20       (2022년 03월 28일 20시 42분 19초)       (Attached)
41 Socket in /run/screen/S-medic01.

Now you can get the screen id and re-attach by that id by typing: screen -r your_screen_id

4. To create screen session with a name

screen -S session_name # Note: use a capital S

You will see your session with name like below:

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1(base) medic01@u20:/data1/kynd$ screen -ls
2There are screens on:
3        3351224.session_name    (2022년 03월 28일 20시 46분 01초)       (Attached)
4        3350892.pts-9.u20       (2022년 03월 28일 20시 42분 19초)       (Attached)
52 Sockets in /run/screen/S-medic01.

Re-attach to your screen session by: screen -r session_name

5. Exit from screen

To exit from screen, simply type exit in your screen session. It will terminate your current screen session and back to normal ssh session