Screen is a really really handy little bit of software I leave running on all the Linux boxes I run.

From the man page:

DESCRIPTION
Screen is a full-screen window manager that multiplexes a physical ter-
minal between several processes (typically interactive shells). Each
virtual terminal provides the functions of a DEC VT100 terminal and, in
addition, several control functions from the ISO 6429 (ECMA 48, ANSI
X3.64) and ISO 2022 standards (e.g. insert/delete line and support for
multiple character sets). There is a scrollback history buffer for
each virtual terminal and a copy-and-paste mechanism that allows moving
text regions between windows.

It goes on a bit more at length. Anyway, the important thing is that it allows you to have more than one terminal session running in a single terminal and swap between them. You can also disconnect from screen and reconnect at a later date, maybe even from a different location (console as opposed to a remote putty session for example) and all the sessions will still be there, as will any programs running within them!

Brief overview:

Now if you have a screen session running under a screen (eg, ssh from within screen on host a to host b where you’re also running screen) and you want to perform a screen command on the remote screen you have to type ctrl+a ctrl+a . Thats an extra ctrl+a for every level of screen down you need to go.

Thats the important commands to remember.

If you use screen -RD to attatch to screen, and someone else is already attatched, then their connection is killed. You can do wierd stuff like shared sessions, but then it gets a bit messy and I’m not going to cover it here.