Nagios: The Complete Guide Tutorial | CHECK-OUT
Nagios Tutorial

Nagios: The Complete Guide Tutorial For Free | CHECK-OUT

Last updated on 10th Jul 2020, Blog, Tutorials

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Logesh (Nagios Engineer )

Logesh has expertise in UNIX, Linux, VLANs, VPNs, protocols, routing, IP address schemes, bandwidth, and network devices. He is a certified professional with 7+ years of experience in their respective domains.

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What is Nagios?

Nagio is a free to use open source software tool for continuous monitoring. It helps you to monitor system, network, and infrastructure. It is used for continuous monitoring of systems, applications, service and business process in a DevOps culture.

Nagios runs plugins stored on the same server. It plugin’s connects with a host or another server on your network or the Internet. Therefore, in the case of failure Nagios core can alert the technical staff about the issues. So that, your technical team performs the recovery process before outage in the business processes.

Why Nagios?

Following are some reasons for using the Nagios software application:

  1. It is used for monitoring the performance issues of servers.
  2. It helps the users of this software application to easily find the root cause of any problem.
  3. It is also used to detect all the possible networks.
  4. We can easily maintain the issues of security and also detect the availability of the services.
  5. This application automatically fix the problems or issues when occurs.
  6. Users can easily run it on any operating system.
  7. Before the failure of a system, it helps you to update the infrastructure.
  8. Using this application, user can quickly detect any type of infrastructure issues.
  9. It also monitors the various servers of database such as SQL Server, MySQL.
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Why Do We Need Nagios?

Here, are Important reasons to use Nagios monitoring tool are:

  • Detects all types of network or server issues
  • Helps you to find the root cause of the problem which allows you to get the permanent solution to the problem
  • Active monitoring of your entire infrastructure and business processes
  • Allows you to monitors and troubleshoot server performance issues
  • Helps you to plan for infrastructure upgrades before outdated systems create failures
  • You can maintain the security and availability of the service
  • Automatically fix problems in a panic situation

How does Nagios work?

Nagios runs on a server where the plug-in is installed and starts running automatically. They further contact the hosts/ server on your network and give the status message in two different manners. One is a web interface and other is SMS and e-mail. Nagios works as a scheduler and runs selected scripts after a repeated time interval. When requirement changes, the previous script will be stored and new scripts will be run depending on needs.

In short, the working of Nagios is based on plug-ins that give the confirm status of server, application or infrastructure issues.

What is continuous monitoring?

Once the application becomes active, the role of continuous monitoring comes into existence. The process is all about taking care of company infrastructure and respond immediately as soon as error detects. The technique, static analysis that is responsible for detecting, responding or reporting the log but the analysis is not much accurate. But, with continuous monitoring, you can perform and respond to each of the activities in the best way.

The process is performed on the continuous (on-going) basis that reports instantly about the risks that can be faced by an organization for its poor infrastructure. You can check the activities of networks and data analytics report when required.

In the above figure, there is no end to a DevOps life cycle, and that is the reason for the infinity symbol. It is all about the ability of an organization to detect, report, respond, contain and mitigate the attack that occurs, in its infrastructure.

Why is continuous monitoring useful?

Continuous monitoring detects system error before they occur. Error impacts on business productivity. Following features explain why continuous monitoring is useful:

  • It detects network errors and system crashes.
  • Entire IT infrastructure and business process can be monitor in a single pass only.
  • It monitors service availability and security.
  • Issues can be fixed automatically as soon as they occur.
  • Notification system to inform the administrator when something goes wrong.
  • It determines the root causes of any problem.

Key Concept

  • Colored are concept, green for ok, yellow for warning and red for critical
  • No performance analysis or display
  • Web interface and notifications
  • Various possibilities for remote check
  • Check using plugin

Features of Nagios

Following are the important features of Nagios:

  • Relatively scalable, Manageable, and Secure
  • Good log and database system
  • Informative and attractive web interfaces
  • Automatically send alerts if condition changes
  • If the services are running fine, then there is no need to do check that host is an alive
  • Helps you to detect network errors or server crashes
  • You can troubleshoot the performance issues of the server.
  • The issues, if any, can be fixed automatically as they are identified during the monitoring process
  • You can monitor the entire business process and IT infrastructure with a single pass
  • The product’s architecture is easy writing new plugins in the language of your choice
  • Nagios allows you to read its configuration from an entire directory which helps you to decide how to define individual files
  • Utilizes topology to determine dependencies
  • Monitor network services like HTTP, SMTP, HTTP, SNMP, FTP, SSH, POP, etc.
  • Helps you to define network host hierarchy using parent hosts
  • Ability to define event handlers which runs during service or host events for proactive problem resolution
  • Support for implementing redundant monitoring hosts

Nagios Architecture

Nagios is a client-server architecture. Usually, on a network, a Nagios server is running on a host, and plugins are running on all the remote hosts which should be monitored.

Nagios Architecture
  1. The scheduler is a component of server part of Nagios. It sends a signal to execute the plugins at the remote host.
  2. The plugin gets the status from the remote host
  3. The plugin sends the data to the process scheduler
  4. The process scheduler updates the GUI and notifications are sent to admins


Nagios plugins provide low-level intelligence on how to monitor anything and everything with Nagios Core. Plugins operate acts as a standalone application, but they are designed to be executed by Nagios Core. It connects to Apache that is controlled by CGI to display the result. Moreover, a database connected to Nagios to keep a log file.

How do plugins work?


Consider the above example-

  • Check_nt is a plugin to monitor a windows machine which is mostly available in the monitoring server
  • NSClinet++ should be installed in every Windows machine that you wants to monitor
  • There is an SSL connection between the server and the host which continuously exchange information with each other

Likewise, NRPE(Nagios Remote plug-in Executor) and NSCA plugins are used to monitor Linux and Mac OS X respectively.


An interface of Nagios is used to display in web pages generated by CGI. It can be buttons to green or red, sound, graph, etc.

When the soft alert is raised many times, a hard alert is raised, then the Nagios server sends a notification to the administrator.

Nagios GUI

Nagios GUI

Install Nagios at AWS

Step 1) Got to and click Continue to Subscribe

Installing Nagios at AWS-Step 1

Step 2) Accept Terms

 Installing Nagios at AWS-Step 2

Step 3) You will see subscription pending message

Installing Nagios at AWS-Step 3

Step 4) Refresh the same page after a few minutes and click “Continue to Configuration

Installing Nagios at AWS-Step 4

Step 5) Keep the settings default and click Continue to Launch

Installing Nagios at AWS-Step 5
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Step 6) Review the settings. Create a new Key and click launch

Installing Nagios at AWS-Step 6

Step 7) Note the public DNS of your instance

Installing Nagios at AWS-Step 7

Step 8) In your windows machine, use the tool putty generator to convert pem file to ppk

Installing Nagios at AWS-Step 8

Step 9) In putty, enter the public DNS

Installing Nagios at AWS-Step 9

Step 10) In Auth section, enter the ppk key and click open

Installing Nagios at AWS-Step 10

Step 11) In terminal,

  1. Enter login name as ubuntu
  2. Run this command sudo htpasswd -c /etc/nagios3/htpasswd.users nagiosadmin
  3. Enter a new password of your choice
Installing Nagios at AWS-Step 11

Step 12) In your browser, Go to location http://<Public DNS>/nagios3 in my case

Enter Username: nagiosadmin

pass: set in the previous step

Installing Nagios at AWS-Step 12

Step 13) Nagios Loads

Installing Nagios at AWS-Step 13-nagios loads

Application of Nagios

Nagios is a health check & monitoring system for a typical Data Centre, comprises all type of equipment’s such as:

  • Server & Network Nodes
  • Application monitoring from a single console
  • Application Monitoring with transaction-level insights
  • Monitor Middleware & Messaging Components
  • Customizable Reports and Dashboards
  • UPS Backup System
  • Bio-Metric Identification System
  • Temperature & Humidity Control System (Sensing Mechanism)
  • CCTV/NVR System
  • Storage Subsystem (NAS&SAN)

Disadvantages of Using Nagios

  • Important feature like wizards or interactive dashboard are only available on Nagios XI, which is quite an expensive tool
  • Nagios core has a confusing interface
  • There’re many configuration files which are very hard to configure for users
  • Nagios can’t monitor network throughput
  • The tool not allows you to manage the network but only allows to monitor the network
  • Nagios makes no difference between various devices like servers, routers, or switches as it treats every device as a host
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  • Continuous monitoring is a process to detect, report, respond all the attacks which occur in its infrastructure
  • Nagio is free to use open source software tool for continuous monitoring
  • Nagio offers effective monitoring of your entire infrastructure and business processes
  • Ethan Galstad uses the ideas and architecture of his earlier work to begin building a new application Nagios which runs under Linux OS
  • Nagios is relatively scalable, Manageable, and Secure
  • Three important components of Nagios architecture are 1) Web Interface (GUI) 2)Nagios Server 3)Plugin
  • Nagios allows application monitoring from a single console with transaction-level insights
  • This tool not allows you to manage the network but only allows to monitor the network

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