[Quick Tips] : Bash scripts to scan and monitor network

Bash scripts to scan and monitor network


1. Scan network subnet

In this example the bash script will scan 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

Execute:
./bash_ping_scan.sh


OUTPUT:
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.


2. Notify when server is down script

Ping bash script example No.2 will send an email to a specified email address when ping cannot reach its destination. System admin can execute this in script regularly with use of a cron scheduler. The script first uses ping command to ping host or IP supplied as an argument. In case that destination is unreachable a mail command will be used to notify 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

Execute:
./check_hosts.sh google.com yahoo.com 192.168.1.2 mylinuxbox N2100


3. Create a monitoring log

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 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

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