in fact you need to know how to make a process run as a deamon, because logging out will still kill the background process.
what I do is launch a script at startup which continually checks for the existence of a file eg. /home/me/signal then sleeps for 1 second. if the file is there it launches another script. creating the file eg. touch /home/me/signal, launches the action. email me if you want more details, or read the bash manpage for more on how to write a script.
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