Monitoring Your Systems with Nagios

Once you have a system that becomes important to your organization, you will want to begin to monitor it to ensure that it is up and running and to be able to measure and create uptime reports for those services for yourself and your supervisors.  The easiest and most cost effective way to do this is by monitoring your systems with Nagios.  All of this can be done easily with a simple Nagios system.

How to Install a Nagios System

Setup Nagios to Monitoring / Monitoring Your Systems with Nagios

Setup Nagios to Monitor Your Important Systems / Monitoring Your Systems with Nagios


Step 1Get a small cloud VPS server from Linode, Rackspace, Digital Ocean, Media Temple, etc… with your favorite Linux operating system.

Step 2Install Nagios and Nagios plugins using the steps in this blog post below.

Step 3 – Configure Nagios to monitor your important services (mail, web, other services).


Nagios Setup Step by Step

It’s All About Geography – Get a VPS

Not only is it important for your important systems to be up, but they need to be available to the important locations.  For example, if you want to be sure that your website is up for all of your customers and the rest of the internet in general.  So, you will want to monitor your website from a location exterior to where it is being hosted.  If it is being hosted from your office, create your monitoring system elsewhere.  If you have your website hosted at a hosting company, you need to install your monitoring system at a different hosting provider.  The easiest way is to choose a VPS somewhere and install on it.  For this example, I did this on a small VPS from Digital Ocean.  When I created my Nagios VPS, I chose CentOS 6.4.

Download Nagios

I typically create a directory somewhere, download the files, then compile and download from there.  For this task, I created the /installs/nagios directory and I download the latest Nagios software which at the time of this writing is 3.5.1 and the plugins are 1.4.16.  I will download Nagios from: and the Nagios plugins from here:

mkdir -p /installs/nagios
cd /installs/nagios

Note:  Download Nagios 4 instead!  Nagios 4 is now out and you can download the latest nagios 4.0.1 using this link:

Note:  Download Naigos Plugins 1.5 instead!  Nagios Plugins 1.5 is now out and you can download the latest from this link:

Install Prerequisites

Before I can compile and install Nagios, I need to install the prerequisites that are used during the compilation.

yum install php
yum install https gcc glib glibc-common gd gd-devel openssl-devel net-snmp net-snmp-utils make

 Create Nagios User

We need a nagios user to be the owner of the Nagios code:

useradd nagios

passwd nagios
Changing password for user nagios.
New password:    <type in a password here>
Retype new password:    <type in a password here> passwd: all authentication tokens updated successfully.

Compile and Install Nagios

With all of the prerequisites done, we should now be able to unzip, compile and install nagios:

gunzip nagios-3.5.1.tar.gz
tar -xvf nagios-3.5.1.tar
cd nagios
make all
make install
make install-init
make install-config
make install-commandmode
make install-webconf


Setup the Admin Contact Information

Because we want to get email alerts when something is down, we need to put our email address in the contacts file.  We do this by editing the /usr/local/nagios/etc/objects/contacts.cfg file with our favorite editor:

define contact{
contact_name       nagiosadmin                   ; Short name of user
use                        generic-contact               ; Inherit default values from generic-contact template (defined above)
alias                      Nagios Admin                  ; Full name of user
email             ; <<***** CHANGE THIS TO YOUR EMAIL ADDRESS ******

Setup a Password to Protect Nagios

We want to protect our Nagios system so that only we can get in with a web browser.  we do this by creating a htpasswd file that will setup a userid and password for us to type in our browser when accessing Nagios.

htpasswd -c /usr/local/nagios/etc/htpasswd.users nagiosadmin

New password:
Re-type new password:
Updating password for user nagiosadmin

restart our apache httpd daemon:

service httpd restart

Compile and Install Nagios Plugins

We are nearly done installing Nagios.  But Nagios needs plugins to check services and hosts.  So it is time to compile and install the plugins:

cd /installs/nagios
gunzip nagios-plugins-1.4.16.tar.gz
tar -xvf nagios-plugins-1.4.16.tar

./configure –with-nagios-user=nagios –with-nagios-group=nagios
make install

Setup Nagios in Services Manager

For Nagios to start at boot time and to make it easier to stop and start, we need to add Nagios to the services manager.  We will use chkconfig to add nagios and enable it in the services manager, then verify our nagios.cfg file is correct, then startup Nagios:

chkconfig nagios on
/usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg
service nagios start

Login to Nagios – Monitoring Your Systems with Nagios

We should now be able to login to the Nagios system we just installed and begin monitoring our Systems with Nagios!  We browse to it using the ipaddress of our Nagios server.  In my case, this is the address of my VPS:  http://<ipaddress>/nagios.  When we login, we will need to use the username and password we set above.

Nagios Management Console Allows you to Create Uptime Reports and Manage your Services and Hosts Monitoring Tasks

Nagios Management Console Allows you to Create Uptime Reports and Manage your Services and Hosts Monitoring Tasks


My next article will be on how to configure and define Nagios Hosts ans Services

Next Step – Define Nagios Hosts and Services.

Click Here to go to the Define Nagios Hosts and Services Article.

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Jeff has 20 years of professional IT experience, having done nearly everything in his roles of IT consultant, Systems Integrator, Systems Engineer, CNOC Engineer, Systems Administrator, Network Systems Administrator, and IT Director. If there is one thing he knows for sure, it is that there is always a simple answer to every IT problem and that downtime begins with complexity. Seasoned IT professional by day, Jeff hopes to help other IT professionals by blogging about his experiences at night on his blog: You can find Jeff on or LinkedIn at: LinkedIn or Twitter at: Twitter

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1 comment for “Monitoring Your Systems with Nagios

  1. Beau
    September 5, 2013 at 8:43 am

    this is perfect! exactly what i needed!

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