screen is a program that allows you to start a session and then detach from that session without killing the session. For example, you could start a job in a screen session, detach and log out, then log in to the same computer from home and reattach to that session.
SPINACH[~]$ screen (shows screen splash screen) SPINACH[~]$ ./findall.py This program will calculate all known perfect numbers... Perfect Numbers ------------------------- 1 ....is not perfect... 2 ....is not perfect... 3 ....is not perfect... 4 ....is not perfect... 5 ....is not perfect... ... ... (hit Ctrl-a d) [detached from 29395.pts-3.spinach] SPINACH[~]$ exit ...3 hours later... SPINACH[~]$ screen -r 38268 ....is not perfect... 38269 ....is not perfect... 38270 ....is not perfect... 38271 ....is not perfect... 38272 ....is not perfect... 38273 ....is not perfect... ... ... SPINACH[~]$ Ctrl-d [screen is terminating] SPINACH[~]$
Note: this is only useful for non-graphical programs, but some students were using xvfb and screen this last semester.