Ping sweep script to scan and monitor network

In this tutorial, we will provide a few Bash scripts to scan and monitor the network using combination of commands such as ping. Obviously, these scripts are no match to a full monitoring dedicated software like nagios, but they could be useful for small home brand networks, where implementing sophisticated monitoring systems can become too much overhead.

In this tutorial you will learn:

• How to scan a network subnet with a Bash script
• How to notify via email when a network host is down
• How to create a network monitoring log in Bash

Software Requirements and Linux Command Line Conventions

Category	Requirements, Conventions or Software Version Used
System	Any Linux distro
Software	N/A
Other	Privileged access to your Linux system as root or via the sudo command.
Conventions	# – requires given linux commands to be executed with root privileges either directly as a root user or by use of sudo command $ – requires given linux commands to be executed as a regular non-privileged user

Scan network subnet

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In this example, the Bash script will scan the network for hosts attached to an IP address 10.1.1.1 – 255. The script will print message Node with IP: IP-address is up if ping command was successful. Feel free to modify the script to scan your hosts range.

#!/bin/bash

is_alive_ping()
{
  ping -c 1 $1 > /dev/null
  [ $? -eq 0 ] && echo Node with IP: $i is up.
}

for i in 10.1.1.{1..255} 
do
is_alive_ping $i & disown
done

Example output:

$ ./bash_ping_scan.sh
Node with IP: 10.1.1.1 is up.
Node with IP: 10.1.1.4 is up.
Node with IP: 10.1.1.9 is up.

Notify when server is down script

In this next ping Bash script example, we will send an email to a specified email address when ping cannot reach its destination. The system admin can execute this in script regularly with use of a cron scheduler.

The script first uses ping command to ping a host or IP supplied as an argument. In case that destination is unreachable, a mail command will be used to notify the system administrator about this event.

#!/bin/bash

for i in $@
do
ping -c 1 $i &> /dev/null

if [ $? -ne 0 ]; then
	echo "`date`: ping failed, $i host is down!" | mail -s "$i host is down!" my@email.address 
fi
done

Example execution syntax:

$ ./check_hosts.sh google.com yahoo.com 192.168.1.2 mylinuxbox N2100

Create a monitoring log

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The last example is a modified version of the previous example. When mail is not configured on the system, the script will create a log file. The core of the script is wrapped into an endless while loop which is set to execute ping check every hour ( 3600 second ).

Modify the script according to your needs. Remove endless while loop when you intend to use this script with cron scheduler.

#!/bin/bash 
 
LOG=/tmp/mylog.log 
SECONDS=3600 

EMAIL=my@email.address 
 
for i in $@; do 
	echo "$i-UP!" > $LOG.$i 

done 
 
while true; do 
	for i in $@; do 

ping -c 1 $i > /dev/null 
if [ $? -ne 0 ]; then 
	STATUS=$(cat $LOG.$i) 
 		if [ $STATUS != "$i-DOWN!" ]; then 
 			echo "`date`: ping failed, $i host is down!" | 
			mail -s "$i host is down!" $EMAIL 

 		fi 
	echo "$i-DOWN!" > $LOG.$i 

else 
	STATUS=$(cat $LOG.$i)
 		if [ $STATUS != "$i-UP!" ]; then 
 			echo "`date`: ping OK, $i host is up!" | 
			mail -s "$i host is up!" $EMAIL

 		fi 
	echo "$i-UP!" > $LOG.$i 
fi 
done 

sleep $SECONDS 
done

Example execution syntax:

$ ./check-server-status.sh google.com yahoo.com 192.168.1.2 mylinuxbox N2100

Closing Thoughts

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In this tutorial, we saw how to use Bash scripts to monitor the state of a network on a Linux system. While not as robust as a dedicated network administration program, Bash still provides us with many tools to perform basic monitoring. This allows us to ping sweep a subnet, monitor nodes on a network, and notify when a host is no longer reachable.