Fact 1: When a terminal (xterm for example) gets closed, the shell is supposed to send a SIGHUP ("hangup") to any processes running in it. This harkens back to the days of analog modems, when a program needed to clean up after itself if mom happened to pick up the phone while you were online. The signal could be trapped, so that a special function could do the cleanup (close files, remove temporary junk, etc). The concept of "losing your connection" still exists even though we use sockets and SSH tunnels instead of analog modems. (Concepts don't change; all that changes is the technology we use to implement them.)
Fact 2: The effect of Ctrl-C depends on your terminal settings. Normally, it will send a SIGINT, but you can check by running stty -a
in your shell and looking for "intr".
You can use these facts to your advantage, using bash's trap
command. For example try running this in a window, then press Ctrl-C and check the contents of /tmp/trapped
. Then run it again, close the window, and again check the contents of /tmp/trapped
:
#!/bin/bash
trap "echo 'one' > /tmp/trapped" 1
trap "echo 'two' > /tmp/trapped" 2
echo "Waiting..."
sleep 300000
For information on signals, you should be able to man signal
(FreeBSD or OSX) or man 7 signal
(Linux).
(For bonus points: See how I numbered my facts? Do you understand why?)
So ... to your question. To "survive" disconnection, you want to specify behaviour that will be run when your script traps SIGHUP.
(Bonus question #2: Now do you understand where nohup
gets its name?)