screen is really simple to use, but it can be hard to get started. It has so many features that the essentials get lost if you try (say) to read the manual. So here they are:

1: Start a new session with screen

This is the first thing to do, but it’s confusing, because when you do it you just get a shell prompt again. What happened? You’re actually in a new shell, inside of screen. To demonstrate, start a long-running command, like cat. Leave it up, and go on to

2: Detach from inside screen with “Ctrl-A d”

You should get a message saying screen detached and a shell prompt. This is the prompt from your old shell: It actually ran the command screen, the stuff between then and now was all inside screen, and now the screen command just exited and we’re back at the old shell. Now you can do whatever, log off, log back in, just don’t reboot, then

3: Reattach screen with screen -r

Hey, hey, we’re back where we were when we ran screen in step 1, and our cat is still there waiting for input! That’s the most fundamental concept, the core of screen: It keeps these pseudo-terminals going for you, while you log off, go to bed, switch computers, whatever. There’s a parent “SCREEN” process that screen made, and as long as that process sticks around, you can go back to your pseudo-terminals with screen -r. There’s one other fundamental:

4: Detach from outside screen with screen -d

When you try to reattach a session which screen already has attached elsewhere, it gives you an error. (Try it from another shell.) Maybe the network kills your connection while you’re in screen. Maybe you absent mindedly left it attached from visiting the Timbuktu regional office. Maybe you had to leave in a hurry and couldn’t do petty housekeeping like detaching your session. But you need to reattach that session here. So screen -d will detach the old connection, and now you can screen -r freely. Try it!

That’s the ultra-basics. When you’re comfortable with them, you can read about how to do copy and paste, multiple windows, multi-display, and lots of other useful features… At leisure. You’ve got the core now.