#!/bin/bash
#
# add ip or hostname space separated
HOSTLIST="example.com 8.8.8.8"

# email report
MAILTO="YOU@gmail.com"
MAILFROM="YOU@example.com"
USER_HOME="/Users/YOU/"

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

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

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

fi
done