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Howto/Screen

Screen

Screen is a great tool which has many uses. You could think about it as a kind of a window manager for your console.

For example, if you wish to run two programs at the same time, without having to open multiple connections to the server, you can do this with screen. Maybe you want to run irssi, while at the same time reading the man-page for irssi or something like that.

Another great thing with irssi is that it allows you to keep your programs running while you are disconnected from the server. This makes it possible to stay connected to IRC and log everything even while your computer is turned off!

However, since screen is so powerful and flexible, and it's all text-only, it can be hard to understand how everything works and get a good overview. It's also easy to start too many screen sessions, and this way locking yourself out from the shell (since you can only have so many processes/connections). If this happens, talk to Independence and he can help you out. Also remember that you are only allowed to run two programs in the background, for example one instance of irssi and one instance of lynx.

Starting, detaching and reattaching a screen session

You can detach a screen when you want to log out, this way your programs will keep running while you are away. If you want to be able to do this, you first have to start your programs in a screen, otherwise you won't be able to detach.

To start a screen session, simply type:

screen

This will spawn a new screen for you. You won't see much of any output at all, the only thing that happens (for me at least) is that the console gets cleared of text. It should look just like a regular login, but this time it is running inside a screen.

Now you can just start the program you want, for example irssi.

When you want to log out, you can detach your program by entering the key combination of Ctrl-A, D (that is Ctrl-A followed by a D). Now your command is running in the background, inside your screen.

You can at this time log out, and come back at a later time to resume your screen, and it will keep running at the server the whole time.

To bring the command to the foreground again (reattach the screen), type:

screen -r

That wasn't too hard, was it? :) Whith the few things you have learned this far, you can really make so much more of your shell experience. It's a truly great tool!

The next step

Now, if you want to run multiple programs at the same time, and easily switch between them, you can create several "windows" in your screen session. To create a new window, use this key combination: Ctrl-A, C. (C for Create).

You should be presented with a brand new prompt, where you can start yet another program! You can create even more windows if you want, but be careful not to start any more than you need. If you create too many, you won't be able to log back in again. Two windows is probably good for most.

To switch between two windows inside a screen, press Ctrl-A, A. This immediately switches back and forth between two different windows (really, it switches to the last used window). If you have more that two windows, you can use Ctrl-A, <space> for stepping forward, and Ctrl-A, <backspace> for stepping backwards. You may also also use Ctrl-A, <0-9> where the number is the window you want to visit. Or you can use Ctrl-A N (b for before, or previous window in the list) and Ctrl-A N (n for next window in list).

If you want to see a list of all the windows for a better overview, press Ctrl-A, ". You can then select a window with the arrow keys and enter it by pressing enter.

If you have more than two windows, it might also be a good idea to name them so you can distinguish them in the list (instead of all being named "bash"). You can do this by pressing Ctrl-A, A.

Exiting

To exit from a window, just type logout or exit (you can also do this by pressing Ctrl-D). If you only have one window, you will exit the screen session and you will get a message like this:

[screen is terminating]

Extra

If you somehow started two independent screen sessions (not windows, but alltogether different sessions) you might not be able to resume the right one just by tying screen -r. In this case, you have to specify screen -r <id>. If you don't need more than one screen (which you probably don't), you can just resume the one you don't want anymore and type exit or logout to destroy it.

Sometimes when the server reboots, your screens "dies". If this happens, you won't be able to reattach it. Instead, you have to clear the old (by doing screen -wipe) one and start a new. More info: FAQ/DeadScreen.

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