How can I check a file exists and execute a command if not?

Question

I have a daemon I have written using Python. When it is running, it has a PID file located at /tmp/filename.pid. If the daemon isn\'t running then PID file doesn\'t exist.

Answer 1

Another approach to solving the problem is a script that ensures that your daemon "stays" alive...

Something like this (note: signal handling should be added for proper startup/shutdown):

$PIDFILE = "/path/to/pidfile"

if [ -f "$PIDFILE" ]; then
    echo "Pid file exists!"
    exit 1
fi

while true; do
    # Write it's own pid file
    python your-server.py ;

    # force removal of pid in case of unexpected death.
    rm -f $PIDFILE;

    # sleep for 2 seconds
    sleep 2;

done

In this way, the server will stay alive even if it dies unexpectedly.