sharing a console

overview

You can use the screen tool to share a console between two users - this is useful for remote collaborative development, and doesn't require nearly as much bandwidth as a desktop-sharing protocol like VNC.

For this document, I'll use the example of user 'Alice' creating a shared console for 'Bob' to join in on.

setting up the system

You'll need a local installation of screen, and make a few permissions changes to allow multi-user mode. The screen binary needs to be setuid-root, and the /var/run/screen directory needs to be at least mode 0755.:

alice $ sudo chmod u+s `which screen`
alice $ sudo chmod 755 /var/run/screen

Note that creating setuid-root binaries on a machine is usually not a good idea. I'd advise against doing this on a machine that hosts untrusted users.

setting up the hosting session

User alice needs to run screen and turn 'multiuser mode' on, then allow user bob to access it.

alice $ screen

And then the keystrokes (C-a is ctrl + a):

C-a : multiuser on
C-a : addacl bob

Now the session is available to Bob to connect - all he needs is the session id. This is shown by

alice $ screen -ls

and will be something like alice/1942.pts-3.localhost.

connecting to the existing session

Once Alice has started screen and given Bob the session-id, he can connect with screen -x:

bob $ screen -S session-id -x

Then Alice's console will be available to Bob. Both users will see the output on the console, both are able to input characters.

curious postscript

screen oringated at the Univerity of Erlangen, Germany. Pictures of Erlangen are over here.