Simple Linux and UNIX system monitoring with ping command and scripts

You can simply monitor your remote system hosted some remote IDC. There may be tons of causes for which system goes out the network.

Understanding ping command

ping is one of the basic and nifty command to test network connection. For example you can send 4 ping request to cyberciti.biz with following command:
$ ping -c 4 cyberciti.biz
$ ping -c 4 router
Output:

PING router (192.168.1.254) 56(84) bytes of data.
64 bytes from router (192.168.1.254): icmp_seq=1 ttl=64 time=1.02 ms
64 bytes from router (192.168.1.254): icmp_seq=2 ttl=64 time=0.824 ms
64 bytes from router (192.168.1.254): icmp_seq=3 ttl=64 time=0.826 ms
64 bytes from router (192.168.1.254): icmp_seq=4 ttl=64 time=0.843 ms

--- router ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3012ms
rtt min/avg/max/mdev = 0.824/0.880/1.027/0.085 ms

Just see output '--- router ping statistics ---', 4 received is key to verify that 4 packets send and received successfully. You can extract 4 received with the following command:
$ ping -c4 router | grep 'received'
Output:

4 packets transmitted, 4 received, 0% packet loss, time 3012ms

Next logical step is to just get number 4 received using awk command:
$ ping -c4 router | grep 'received' | awk -F',' '{ print $4}'
Output:

4 received 

Last step is to just get 4 number and remove received word:
$ ping -c4 router | grep 'received' | awk -F',' '{ print $2}' | awk '{ print $1}'
Output:

4 

Shell script to system monitoring with ping command

Now you know how to obtained received packets, it is time to automate entire process with simple script. Here is sample script (download link):

#!/bin/bash
HOSTS="cyberciti.biz theos.in router"

COUNT=4

for myHost in $HOSTS
do
  count=$(ping -c $COUNT $myHost | grep 'received' | awk -F',' '{ print $2 }' | awk '{ print $1 }')
  if [ $count -eq 0 ]; then
    # 100% failed 
    echo "Host : $myHost is down (ping failed) at $(date)"
  fi
done

You can download complete working script which sends an email alert here.

Setup Cron job

In order to run this script every 30 minutes (or as per your requirements), you need to install a script as cron job:
$ chmod +x /path/to/monitorHost
Install the monitorHost script as crontab using the editor:
$ crontab -e
Append the following cronjob entry:
# Monitor remote host every 30 minutes using monitorHost
30 * * * * /home/vivek/bin/monitorHost
Save and close the file.