#!/bin/bash
#
# add ip or hostname space separated
HOSTLIST="1.2.3.4 www.somehost.com 12.34.56.78 otherhost.org"

# email report
MAILTO="[email protected]"
MAILFROM="[email protected]"


# number of ping requests,  timeout in seconds and a threshold
COUNT=5
TIMEOUT=2
MAXFAIL=2

# ip to use to check if *this* machine can ping (8.8.4.4 is google dns)
CONTROLIP="8.8.4.4"

#
let "THRESHOLD = $COUNT - $MAXFAIL"

ping -c 1 -W $TIMEOUT $CONTROLIP > /dev/null && for HOST in $HOSTLIST
do
  count=$(ping -c $COUNT -W $TIMEOUT $HOST | grep 'received' | awk -F',' '{ print $2 }' | awk '{ print $1 }')
  if [ $count -lt $THRESHOLD ] ; then
    # too many ping failed but control is up: if previously up->failed-once, if failed-once->down

    if [ -f .up-$HOST ];    then
            mv  .up-$HOST .failed-once-$HOST
        else
            if [ -f .failed-once-$HOST ]; then
                    mv  .failed-once-$HOST .down-$HOST
                    echo "Host : $HOST is down (ping failed) at $(date)" | mailx -r $MAILFROM -s "Alert: $HOST is down" $MAILTO
                else
                # is it down or a new host -> failed-once
                    if [ ! -f .down-$HOST ];    then
                            touch .failed-once-$HOST
                    fi
            fi
    fi

  else
    # most ping ok, host is up: if !up -> up

    if [ ! -f .up-$HOST ]; then
            if [ -f .failed-once-$HOST ]; then
                rm  .failed-once-$HOST
            else
                if [ -f .down-$HOST ]; then
                    rm  .down-$HOST
                    echo "Host : $HOST is up again (ping ok) at $(date)" | mailx -r $MAILFROM -s "Alert: $HOST is UP again" $MAILTO
                fi
            fi
    touch .up-$HOST
    fi

  fi
done