The `screen` [command][1]. It basically saves your command line session for when you come back. It's sort of a terminal manager, like a window manager. That way, in a single terminal session, you can have multiple virtual terminals going on. It's very cool. 

If one uses `screen`, this shell function (put it into `.bashrc`) is extremely useful:

 function scr {
 if screen -ls | grep -q Main; then
 # reattach to Main: 
 screen -xr Main
 else
 # name session "Main":
 screen -S Main
 fi
 }

upon typing `scr`, it will check if your main session exists and will attach to it. Otherwise it will create it. 

 [1]: /http://www.rackaid.com/resources/linux-screen-tutorial-and-how-to/