How To Install and Configure Nagios On CentOS 6.5

Nagios is an open source software that can be used for network and infrastructure monitoring. Nagios willmonitor servers, switches, applications and services. It alerts the System Administrator when something went wrong and also alerts back when the issues has been rectified.

With Nagios you can:

- Monitor your entire IT infrastructure.
- Identify problems before they occur.
- Know immediately when problems arise.
- Share availability data with stakeholders.hypothetical question
- Detect security breaches.
- Plan and budget for IT upgrades.
- Reduce downtime and business losses.

Scenario

In this tutorial i am going to use two systems as mentioned below.

Nagios server:

Operating system : CentOS 6.5 minimal installation
IP Address       : 192.168.0.155/24

Prerequisites

Before installing Nagios, make sure that you’ve a properly installed and configured LAMP stack in your server. to install and configure LAMP server, see my previous link.

After that..

# yum install gd gd-devel gcc glibc glibc-common 

Install Nagios

I tested this how-to on CentOS 6.5 minimal server, although it should work on all RHEL 6.x and its clones like CentOS 6.x and Scientific Linux 6.x.

 Nagios will not be found in CentOS official repositories, so let us add the EPEL repository to install nagios. 

# yum install nagios

 Note: It worked for me either if i keep SELINUX and iptables enable or disable.

Configure Nagios

Add the admin mail address in the nagios contact file to receive alerts from nagios server. To do that edit file /etc/nagios/objects/contacts.cfg,

# vi /etc/nagios/objects/contacts.cfg

 Find the following line and enter the email id:

[...]
email                           admin@geniusansh.com ;
[...

 Save and close the file. Then Edit file /etc/httpd/conf.d/nagios.conf 

# vi /etc/httpd/conf.d/nagios.conf

 And edit the following lines if you want to access nagios administrative console from a particular IP series. Here i want to allow nagios administrative access from 192.168.0.0/24 series only.

[...]
## Comment Lines 15 & 16 ##
#   Order allow,deny
#   Allow from all

## Uncomment and Change lines 17,18 & 19 as shown below ##
Order deny,allow
Deny from all
Allow from 127.0.0.1 192.168.0.0/24
[...]

 Set nagiosadmin password

# htpasswd /etc/nagios/passwd nagiosadmin
New password:
Re-type new password:
Updating password for user nagiosadmin

 Start nagios and httpd services and let them to start automatically on every boot.

# service nagios start
# service httpd start
# chkconfig nagios on
# chkconfig httpd on 

Access Nagios admin console

Open nagios administrator console with URL http://nagios-server-ip/nagios and enter the username as nagiosadmin and its password which we created in the earlier steps.

This is how Nagios administrative console looks:

Click on the “Hosts” section in the left pane of the console. You will see the no of hosts to be monitored by Nagios server. Initially, the nagios server (localhost) itself will only be monitored.

Click on the monitoring host to display

Add Monitoring targets to Nagios server

Now let us add some clients to monitor by Nagios server. To do that we have to install nrpe and nagios-plugins in our monitoring targets.

On CentOS/RHEL/Scientifc Linux clients:

Like i said before, you have to add EPEL repository in your CentOS/RHEL/Scientific Linux 6.x clients to install nrpe package.

Install “nrpe” and “nagios-plugins” packages in client systems to be monitored.

# yum install nrpe nagios-plugins-all openssl

Configure Monitoring targets

Edit /etc/nagios/nrpe.cfg file

# vi /etc/nagios/nrpe.cfg

Add your Nagios server ip address

[...]
## Line 81 - Add the Nagios server IP ##
allowed_hosts=127.0.0.1 192.168.0.155
[...]

 Start nrpe service:

# service nrpe start
# chkconfig nrpe on

 Now go back to your Nagios server to add the clients to be monitored through nagios server. Edit“/etc/nagios/nagios.cfg” file

# vi /etc/nagios/nagios.cfg

 and uncomment the following lines.

## Line 52 - Uncomment ##
cfg_dir=/etc/nagios/servers

 Create a directory called “servers” under “/etc/nagios/”.

# mkdir /etc/nagios/servers

Create config file to the client to be monitored:

# vi /etc/nagios/servers/clients.cfg

define host{

use                             linux-server

host_name                       client

alias                           client

address                         192.168.0.155  ## Client IP ##

max_check_attempts              5

check_period                    24x7

notification_interval           30

notification_period             24x7

}

 Finally restart nagios service.

# service nagios restart

Now open the nagios admin console in the browser and navigate to “Hosts” section in the left pane. You will see the newly added client will be visible there. Click on the host to see if there is anything wrong or alerts.

That's it. Enjoy UR Self Friends!!!