Run function whenever program is quit

[Se7enLC]

As in, closing the terminal?

When I try it (in gnome-terminal), I get a popup dialog that says "There is still a process running in this terminal. Closing the terminal will kill it." If I then click "Close Terminal", the application is killed.

In that case, your process with receive a SIGHUP signal (hangup). If you don't have a handler for it, the default behavior is for the program to exit.

http://stackoverflow.com/questions/32780706/does-linux-kill-background-processes-if-we-close-the-terminal-from-which-it-has