Of course SNMP + Nagios is a better choice for mission critical monitoring than simply pinging something like I do here.
Here is the script;
#!/bin/bash TIMEOUT=5 # Number of failed attempts before sending email STATUSDIR=/tmp/vpn # Status files are written here ADDRESS=$1 # The target address to be monitored EMAIL=$2 # Optional email address to send alerts to if [ ! -d $STATUSDIR ] ; then mkdir -p $STATUSDIR fi if [ ! -f $STATUSDIR/$ADDRESS ] ; then `echo "0" > $STATUSDIR/$ADDRESS` fi EXPECTEDCOUNT=`cat $STATUSDIR/$ADDRESS` if ping -c 1 -w 5 "$ADDRESS" &>/dev/null ; then DOWNCOUNT=0 else DOWNCOUNT=$(($EXPECTEDCOUNT+1)) fi echo "Expected count is :"$EXPECTEDCOUNT echo "Down count is :"$DOWNCOUNT # Something has changed if [ ! $EXPECTEDCOUNT = $DOWNCOUNT ] ; then if [ $DOWNCOUNT = 0 ] ; then STATUS="UP" else STATUS="DOWN" fi MSG="vpn-link: "$ADDRESS" is "$STATUS" (count="$DOWNCOUNT")" logger $MSG # if the change was to 0 or TIMEOUT then trigger an email if [ $DOWNCOUNT = 0 -o $DOWNCOUNT = $TIMEOUT ] ; then # If the expected count has not reached the timeout setting then # we dont want to send email EXPECTEDCOUNT=$(($EXPECTEDCOUNT+1)) if [ $EXPECTEDCOUNT -ge $TIMEOUT -a -n "$EMAIL" ] ; then echo $ADDRESS" is "$STATUS": Sending email" mail -s "$MSG" $EMAIL < /dev/null > /dev/null fi fi echo $DOWNCOUNT > $STATUSDIR/$ADDRESS fiTo use it simply place the script in a convenient location such as /usr/sbin and create an entry in your system crontab like this;
* * * * * brett /usr/sbin/vpn-mon 192.168.1.2 email@example.com >> /dev/null 2>&1
This will ping test to 192.168.1.2 as user "brett" every minute and send email alerts to firstname.lastname@example.org
By default the script will send an email after the test has failed 5 consecutive times. This can be changed by editing the script and changing the TIMEOUT variable.