Screen is neat. It allows you to start long running processes (like fsck or a big network copy) and then log out.
Also if you're getting into your box over ssh or something, it preserves the login if the connection goes down. I imagine that it survives the death of X and other unfortunate events also.
Screen's neat. But I can never remember how to use it when I need it. This is for me:
$ sudo apt-get install screen
Start a terminal.
In this terminal type:
There will be a screen full of crap: Press Return to make it go away, and wait a second or so.
Apparently you will be back at a terminal. But it is really a screen session.
Start a long-running task:
Detach from your session using C-a d (ie, hold down control, press a, release control, press d)
You are back at your terminal:
Now switch to a virtual console with Alt-Ctrl-F1
Reattach to the screen session
$ screen -r
You should have htop running before your eyes.
Detach from your session with C-a d
Switch back to X with Alt-Ctrl-F7
Open a terminal
Reattach to screen with
$ screen -r
Exit from htop with F10 (actually your terminal emulator may catch F10 and do something with it. Getting out of htop is then left as an exercise for the reader.)
You are back at a terminal which is really a screen session
Exit from the screen session with
Everything is back to normal.
Here's an ever so slightly less basic tutorial: