sudo apt-get install screen
You will now have a new console prompt. Anything you do in here will continue to run after your SSH session closes. When you reconnect with SSH later:
You are now reconnected to your screen session, which continued running while you were gone.
If you create more than one screen session, you'll get a list of all the screen sessions currently running when you do
screen -dr as above - just do
screen -dr pid (where pid is the pid number of the session you want to reconnect to) in order to choose one.
exit while in a screen session will close the screen session for good, just as it would in a normal SSH or other console session.