Bash Script PID file locking

bash-pid.md

Pattern below allows for a bash script to be called via, say, cron and check to see if it is already running.

Useful for things like rsync tasks.

PIDFILE=/var/run/myscriptname.pid

if [ -f $PIDFILE ]
then
  PID=$(cat $PIDFILE)
  ps -p $PID > /dev/null 2>&1
  if [ $? -eq 0 ]
  then
    echo "Process already running"
    exit 1
  else
    ## Process not found assume not running
    echo $$ > $PIDFILE
    if [ $? -ne 0 ]
    then
      echo "Could not create PID file"
      exit 1
    fi
  fi
else
  echo $$ > $PIDFILE
  if [ $? -ne 0 ]
  then
    echo "Could not create PID file"
    exit 1
  fi
fi


# Main script ... Do work here

...

# End

rm $PIDFILE