Send bash script into background on start

Question

with all the kind replies to my last question I have been able to create a small script to check temperatures on my NAS but now I am struggling on sending it to the background. When I try to start my script with

sh temp_check.sh start

I get an error pointing to this line

$0 background &

and I can't figure out why :/ This is my whole script

#!/ffp/bin/sh
#
#check CPU and HDD temperature and shutdown if too hot

#Settings
cpu_high=60
hdd_high=50

NAME="temp_check"
PIDFILE="/var/run/$NAME.pid"

Background() {
   echo $$ >$PIDFILE
   exec >/dev/null 2>&1
   trap "rm -f $PIDFILE ; exit 0" INT TERM EXIT

   while true; do
       STATE=$(hdparm -C /dev/sda1 | grep "drive state" | awk '{print $4}')
       if [ "$STATE" = "active/idle" ]; then
           hdd_temp=$(/usr/local/zy-pkgs/bin/smartctl -A -d marvell /dev/sda | grep 194 | cut -d: -f3 | awk '{print $10}')
           cpu_temp=$(i2cget -y 0x0 0x0a 0x07)
           printf -v cpu_res "%d" "$cpu_temp"
           if [[ $cpu_res -lt $cpu_high && $hdd_temp -lt $hdd_high ]]; then
           #echo "CPU und HDD Temperaturen in Ordnung"
           sleep 30
           else
           halt
           fi
       else
           cpu_temp=$(i2cget -y 0x0 0x0a 0x07)
           printf -v cpu_res "%d" "$cpu_temp"
           if [ $cpu_res -lt $cpu_high ]; then
               #echo "CPU Temperatur in Ordnung - HDD im Standby Modus"
               sleep 30
           else
               halt
           fi
       fi
   done
   }

   case $1 in
       start)
           [ -f $PIDFILE ] && [ -f /proc/` cat $PIDFILE `/cmdline ] && echo "already running.       Aborting." && exit 1
           $0 background &
           echo "Starting $NAME..."
       ;;
       stop)
           kill -9 ` cat $PIDFILE ` >/dev/null 2>&1
           echo "Stopping $NAME ` cat $PIDFILE ` "
       ;;
       status)
           [ -f $PIDFILE ] && [ -f /proc/` cat $PIDFILE `/cmdline ] && echo "running as ` cat $PIDFILE ` " && exit 0
           echo "not running"
       ;;
       background)
           Background
       ;;
       *)
           echo "use $0 [ start | stop | status ]"
       ;;
   esac

Any help is appreciated

Cheers Moritz

Answer 1

One possible error is, that the script is not executable. If this is the case, you can either fix the line to

/bin/sh $0 background &

or make the script executable with

chmod a+x temp_check.sh

Answer 2

maybe it helps, if you change your Background() function to something like

Background()
{ (
...
) &
}

and just call Background in your "start". That's much simpler.