How to inplement supervise using bash script - bash

Question

supervise is one of the powerful tool in daemontools, I wonder how to implement it using bash script. Anyone has suggestions? I need help!

Answer 1

supervise performs a number of tasks, and interoperates with svscan, svcok, svstat.
A fully-featured implementation in bash would be non-trivial, but a daemon-restarting script is a fairly straight-forward task.
#!/bin/bash
DAEMON=/usr/sbin/whatever # "/bin/sleep" for demo
DAEMON_ARGS="xxx" # "15" for sleep demo
case "$1" in
start)
echo "Starting $DAEMON"
(
trap 'logger -i -p daemon.info "INFO: $DAEMON shutting down..."; exit 1' 1 2 3 15
logger -i -p daemon.info "INFO: Starting $DAEMON"
while : ; do
$DAEMON $DAEMON_ARGS &
pid=$!
echo $pid > /var/run/mydaemon.pid
wait $pid
rc=$?
logger -i -p daemon.warn "WARNING: $DAEMON exited, rc=$rc"
sleep 1 # adjust as required
logger -i -p daemon.warn "WARNING: Restarting $DAEMON"
done
) &
echo $! > /var/run/myscript.pid
;;
stop)
echo "Stopping $DAEMON"
[ -f /var/run/myscript.pid ] && kill $(</var/run/myscript.pid)
[ -f /var/run/mydaemon.pid ] && kill $(</var/run/mydaemon.pid)
;;
esac
The above has pretty much no error handling, doesn't properly do real daemon things like chdir() and close unused FDs, but it does log via logger/syslog so you can see what it's doing. It assumes $DAEMON does not fork into the background itself (as does supervise).
You haven't stated your platform, but if you want something really, really simple, inittab may do the trick, see how to use inittab to auto-restart a PHP programme? for some tips. Otherwise we're veering out of Stack Overflow territory, so check out https://unix.stackexchange.com/ .

Answer 2

I changed the code provided by mr.spuratic around a little bit:
echo "true" > $STATUSFILE
case "$1" in
start)
echo "Starting $DAEMON_NAME"
(
trap 'logger -t italoService "INFO: $DAEMON_NAME shutting down..."; exit 1' 1 2 3 15
logger -t italoService "INFO: Starting $DAEMON_NAME"
while : ; do
#do_start
read STATUS <$STATUSFILE
if [ "$STATUS" = "false" ] ; then
logger -t italoService "INFO: $DAEMON_NAME stopped by user"
break
fi
$DAEMON $DAEMON_OPTS &
pid=$!
echo $pid > $PIDFILE
logger -t italoService "WARNING: pid File: $pid"
wait $pid
rc=$?
logger -t italoService "WARNING: $DAEMON_NAME exited, rc=$rc"
sleep 1 # adjust as required
read STATUS <$STATUSFILE
if [ "$STATUS" = "true" ] ; then
logger -t italoService "WARNING: Restarting $DAEMON_NAME"
fi
done
) &
echo $! > $PIDFILE
;;
stop)
echo "Stopping $DAEMON_NAME"
echo "false" > $STATUSFILE
[ -f $PIDFILE ] && kill $(<$PIDFILE)
[ -f $PIDFILE ] && kill $(<$PIDFILE)
;;