How to Create Own Nagios Plugin using Bash Shell Script

How to Create Own Nagios Plugin using Bash Shell Scripts. This is useful for monitoring infrastructure as your own setup. This tutorial will help you to understand, how to write a script and use them with NRPE and Nagios for monitoring.

Step 1 – Understand Return Codes

Every Nagios plugin must return with a status code which is called return code. On the basis of return codes, Nagios core service takes decisions and appropriate action for the corresponding host or service.

Hosts:

Return Code / Host status
0 => UP
1 => DOWN
Other Maintains last known state

Services:
Return code / Service status
0 => OK
1 => WARNING
2 => CRITICAL
3 => UNKNOWN
Other CRITICAL : unknown return code

Step 2 – Install NRPE Client

Let’s install the NRPE client on your system using the following commands.

sudo apt-get update
sudo apt-get install nagios-nrpe-server nagios-plugins

The above commands are for Debian based systems. To install NRPE on Redhat based system, visit this tutorial.

Step 3 – Write A Shell Script

Now the time to write a shell script to monitor any service on your system. For this example below script will monitor the disk space uses.

vim /usr/lib/nagios/plugins/check_disk_uses.sh

Add the below script.

#!/bin/bash ### ======================================================================= ### ### A nagios plugin to check disk uses for given disk or mountpoint ### ### Uses: ./check_disk_uses.sh / ### ### ./check_disk_uses.sh /mnt ### ### ./check_disk_uses.sh /dev/sda1 ### ### ======================================================================= ### ### ======================================================================= ### ### FUNCTIONS ### ### ======================================================================= ### calculate_disk_uses(){ USED_DISK_SPACE=`df -h ${MOUNT_POINT} | grep -v Filesystem | awk '{print $5}' | sed 's/%//g'` case ${USED_DISK_SPACE} in [1-80]*) echo "OK - ${USED_DISK_SPACE}% of disk space used." exit 0 ;; [81-85]*) echo "WARNING - ${USED_DISK_SPACE}% of disk space used." exit 1 ;; [86-100]*) echo "CRITICAL - ${USED_DISK_SPACE}% of disk space used." exit 2 ;; *) echo "UNKNOWN - ${USED_DISK_SPACE}% of disk space used." exit 3 ;; esac } ### ======================================================================= ### ### SCRIPT EXECUTION START HERE ### ### ======================================================================= ### if [[ -z "$1" ]] then echo "Missing parameters! Syntax: ./`basename $0` mount_point/disk" exit 3 else MOUNT_POINT=$1 fi calculate_disk_uses ### ======================================================================= ### ### END OF SCRIPT ### ### ======================================================================= ###12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152#!/bin/bash ### ======================================================================= ######     A nagios plugin to check disk uses for given disk or mountpoint     ######     Uses: ./check_disk_uses.sh /                                        ######           ./check_disk_uses.sh /mnt                                     ######           ./check_disk_uses.sh /dev/sda1                                ###### ======================================================================= ### ### ======================================================================= ######                         FUNCTIONS                                       ###### ======================================================================= ### calculate_disk_uses(){ USED_DISK_SPACE=`df -h ${MOUNT_POINT} | grep -v Filesystem | awk '{print $5}' | sed 's/%//g'` case ${USED_DISK_SPACE} in [1-80]*) echo "OK - ${USED_DISK_SPACE}% of disk space used." exit 0 ;; [81-85]*) echo "WARNING - ${USED_DISK_SPACE}% of disk space used." exit 1 ;; [86-100]*) echo "CRITICAL - ${USED_DISK_SPACE}% of disk space used." exit 2 ;; *) echo "UNKNOWN - ${USED_DISK_SPACE}% of disk space used." exit 3 ;; esac} ### ======================================================================= ######                         SCRIPT EXECUTION START HERE                     ###### ======================================================================= ### if [[ -z "$1" ]] then        echo "Missing parameters! Syntax: ./`basename $0` mount_point/disk"        exit 3else        MOUNT_POINT=$1fi calculate_disk_uses ### ======================================================================= ######                         END OF SCRIPT                                   ###### ======================================================================= ###

Now set the execute permission on the new script.

chmod +x /usr/lib/nagios/plugins/check_disk_uses.sh

Step 4 – Update NRPE Configuration

Now edit NRPE configuration file /etc/nagios/nrpe.cfg and add your command to monitor some disk of your system.

command[check_disk_uses]=/usr/lib/nagios/plugins/check_disk_uses.sh /dev/sda1

You can call check_disk_uses command from Nagios server using check_nrpe command and get the results back.

Step 5 – Test with Check_Nrpe Command

Now, run the below command from your Nagios server, where 192.168.1.100 is the IP of the NRPE client system.

./check_nrpe -H 192.168.1.100 -c check_disk_uses

OK - 22% of disk space used.