How to Create Nagios Plugins With PHP On Ubuntu 12.10

Introduction

 

Nagios is an open source monitoring software application that helps organizations to prevent IT infrastructure problems. It can be used with Linux as well as other Unix variants.

In this tutorial, you will learn how to create Nagios plugins with PHP. Here, I will be using Ubuntu 12.10.

 

Initial Set Up

 

Before getting into the creation of Nagios plugins, you have to first install NRPE on client VPS. NRPE stands for Nagios Remote Plugin Executor.

NRPE can be installed using the following command:

apt-get install -y php5 nagios-nrpe-server
useradd nrpe && update-rc.d nagios-nrpe-server defaults

 

Creation of PHP Script

 

PHP programming language allows us to create scripts and install additional libraries. Here, we will be creating a script which will check disk usage and throw alert if it is over 85%.

The script will look like this:

#!/usr/bin/php
<?php
$used_space=chop(shell_exec("df -h / | grep -v Filesystem | awk '{print $5}'")); 

switch ($used_space) {
        case "$used_space" < "85%":
        print "OK - $used_space of disk space used.";
        exit(0); 

        case "$used_space" == "85%":
        print "WARNING - $used_space of disk space used.";
        exit(1);

       case $used_space > "85%":
       print "CRITICAL - $used_space of disk space used.";
       exit(2);

       default:
       print "UNKNOWN - $used_space of disk space used.";
       exit(3);
}
?>

This script has to be saved in the same directory as other Nagios plugins, /usr/lib/nagios/plugins/ checkdiskspace.php.

 

Make it executable:

chmod +x /usr/lib/nagios/plugins/checkdiskspace.php

You can customize the script to apply different logic to trigger alerts and exit codes or return codes.

Here is the list of Nagios Return Codes:

Exit Codes / Return Codes Status
0 OK
1 WARNING
2 CRITICAL
3 UNKNOWN

 

Configure NRPE

 

Now that we are done creating the script, we have to add the script to nrpe configuration /etc/nagios/nrpe.cfg on client host. For that, we will first delete the original config file (/etc/nagios/nrpe.cfg) and update it with the following lines of code:

log_facility=daemon
pid_file=/var/run/nagios/nrpe.pid
server_port=5666
nrpe_user=nrpe
nrpe_group=nrpe
allowed_hosts=198.211.117.251
dont_blame_nrpe=1
debug=0
command_timeout=60
connection_timeout=300
include_dir=/etc/nagios/nrpe.d/

command[checkdiskspace_php]=/usr/lib/nagios/plugins/checkdiskspace.php

You have to specify the correct values for allowed_hosts, which should be the IP of monitoring server.

Restart the Nagios nrpe service:

service nagios-nrpe-server restart

 

Set Up on Nagios Monitoring Server

 

In this step, we will add a new command to check Nagios on monitoring server. For that, we have to  update the commands file /etc/nagios/objects/commands.cfg.

 

define command{
        command_name    checkdiskspace_php
        command_line    $USER1$/check_nrpe -H $HOSTADDRESS$ -c checkdiskspace_php
        }

This will use nrpe to make TCP connections to port 5666 and will run the command ‘checkdiskspace_php’ which we already defined in /etc/nagios/nrpe.cfg on remote host.

Now we will add this check to Nagios configuration file for client VPS. In this tutorial, we will be using ‘UbuntuDroplet’ as server for monitoring and will update /etc/nagios/servers/UbuntuDroplet.cfg with following lines of code:

define service {
        use                             generic-service
        host_name                       UbuntuDroplet
        service_description             Custom Disk Checker In PHP
        check_command                   usedspace_php
        }

Once the changes are done, you should restart the Nagios:

service nagios restart

Verify whether the new check is working or not:

nagios-ubuntu-php-check

 

 

 

That’s it!

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