Nagios Interview Questions And Answers

TOP 60 Nagios Interview Questions And Answers

Commonly asked Nagios Interview Questions And Answers

Frequently asked Nagios Interview Questions And Answers are as follow-

Q1) What is Nagios?

Nagios commonly known as the Nagios core is the open-source software that is designed to monitor networks, systems, applications, and infrastructures. The software directly sends the track down all the changes in the subject and send alerts if necessary.

Q2) How Nagios help DevOps professionals?

Nagios was designed in the first place to monitor applications, networks, and infrastructures. The software automatically keeps an eagle eye and immediately report in case of failure. The quick response helps the DevOps professional to track down and resolve the problem in the early stages before it can cause any serious damage to the organization.

Q3) What makes Nagios an ideal tool for continuous monitoring?

The below features of the Nagios is what makes it an ideal tool for continuous monitoring:

Automatic problem fixing

Infrastructure upgrades

Business process and infrastructure monitoring

Quick respond to the system issues

Q4) Write down some of the names of the Nagios monitoring tool for Linux mentoring?

When you are using the Nagios to monitor the Linux environment then you need to understand that you are using one of the best tools on the planet. The complete package of Nagios includes service state, file system usage, system metrics, process state, and more.

Q5) How Icinga is related to the Nagios?

Icinga is also an open-source software that is used to monitor the networks and applications. The core objective of designing Icinga in the first place to lift up the Nagios back in 2009. But it works as a separate monitor software.

Q6) Describe the active and passive check in Nagios

In the Nagios, an active check is leveraged to “poll” a service or device for the status information every once in a while. Nagios basically supports the way to host down the devices and services passively. The key feature of the passive check is it can only be performed by the external applications.

Q7) Explain OID Nagios?

Simple Network Management Protocol (SNMP)- a network protocol that is also designed for the monitoring purpose uses the Object Identifiers to define the Management Information Base.

Q8) Can you use Nagios to monitor the window machine?

Yes, you can use Nagios to monitor the window machine. However, if you are doing it for the first time then you have to follow the given steps:

Set the Nagios to monitor the window system

Add a separate host and server for the window monitoring

Q9) Describe the Nagios XI?

On the current basis, Nagios XI is one of the most powerful monitoring software in the market. when it comes to monitoring critical infrastructures such as network protocols, applications, services, systems metrics, and network protocols experts only rely upon the Nagios XI.

Q10) Highlights the benefits of using Nagios for monitoring?

There are various benefits of using Nagios software for critical monitoring. The list of benefits includes:

Infrastructure updates before the outdated system cause any sort of failure

Automatic tracking and troubleshooting of problem

Coordinate responses

Continuously Monitor infrastructure without any break

Response to issues on an immediate basis

Q11) Explain what active check means?

Active check is the globally recognized way to monitor the hosts and services. Both Nagios XI and Nagios core use it on the pre-determined schedule.

Q12) Describe the Nagios Network Analyzer?

A network analyzer is a crucial aspect of the Nagios software that allows it to deeply scan the entire system in a search of any potential threat. The quick and reliable scan allows system admin to gather necessary data regarding the health of the system and granular data through network analysis.

Q13) Highlight the primary benefits of monitoring the websites with Nagios?

The key benefits of monitoring websites with Nagios are given below:

It enhances the website availability

Increase website performance

Quick detection of online threats such as bugs and hijacking

Q14) Name down some databases that support Nagios monitoring?

There are a number of databases that support Nagios and some of them are mentioned below:



Microsoft SQL software


Q15) Write down the protocols that support Nagios

Nagios supports the number of protocols monitoring including; SMTP Monitoring, IPMI Monitoring, FTP Monitoring, LDAP Monitoring, POP Monitoring, and DNS monitoring.

Q16) what do you understand by the fact that Nagios is object-oriented?

As already mentioned above, Nagios is open-source object-oriented monitoring software. Here the term “object-oriented” means that users can create the object definitions in the Nagios that inheritance from other objects. This essential feature of the Nagios further simplifies the complex relationship between components.

Q17) Can I use Nagios for both cloud computing and cloud monitoring?

Yes, Nagios has a reputation as one of the best monitoring software in the market and you can use it for various monitoring purposes including both virtual and physical.

Q18) state the name of any four virtualization platforms that supports Nagios?

VMware, Amazon EC2, Xen and Microsoft Virtual PC are some of the most common examples of the virtualization platforms that support the Nagios monitoring.

Q19) Do you know the port numbers Nagios use to monitor its clients?

Yes, the Nagios uses port number; 5666, 5667 and 5668 to monitor its clients.

Q20) Describe the process to verify the Nagios configuration?

If you want to configure the Nagios, then you have to run it with the -v command line with option like: nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg.

Q21) Define the objects in Nagios?

In the Nagios, objects refer to all the elements that are involved in the entire monitoring and alerting logic.

Q22) What are the types of objects you can witness in Nagios?

The types of objects you can witness in the Nagios include; Services, Hosts, commands, host groups, contact, time periods, and notification escalations.

Q23) How can you use plugin X in Nagios?

Just like any other plugin, you have to download plugin X from the official website of Nagios which is Once downloaded, you can run it manually to see if it is working correctly.

Q24) When it comes to monetary terms what is the main difference between Nagios Core and Nagios XI?

Well, when it comes to monetary terms, Nagios Core is the free open source version while Nagios XI is the paid version limited to the individual who held the license.

Q25) What is the current Nagios state type?

On the current basis, the monitoring host and services are determined by the two major components
First: Status of the host and service
Second: Types of the state the host or service

Q26) What are the two main state types in Nagios?

The Nagios have two key state types; soft states and hard states.

Q27) Define NRPRE in Nagios?

The term NRPE stands for the Nagios Remote Plugin Executor addon which is specifically designed by the experts to execute Nagios plugins on the Linux machines.

Q28) What database format Nagios support to store status data?

RRD is the database format Nagios support and uses to store the status data.

Q29) Write down the components of NDO Utilities?

The NDO utilities are the right mixture of the:

NDOMOD Event Broker Module


LOG2NDO Utility

NDO2DB Daemon

Q30) Can we monitor the operating system through Nagios?

Yes, you can monitor any operation system through Nagios as long as it supports the software.

Q31) What is the base language for nagios core?

PHP+CGI, Requires Apache as webserver to run php and cgi

Q32) What is the default credentials of nagios?

User and Password : nagiosadmin

Q33) Which location do we place the plugins for nagios?

Location is /usr/lib64/nagios/plugins

Q34) What is inheritance in nagios?

Consider the following definition

define host{

name linux-box

use generic-host

check_command check-host-alive


Here in the line “use generic-host” is the concept of inheritance as it will grab all the properties of generic-host which is already defined in templates.cfg

Q35) Suppose I need all host definition file to be read by nagios instead of mentioning each and every host definition file location in configuration file.

Use cfg_dir=”Directory Location” so that it will consider all configuration under that directory.

Q36) While setting-up nrpe, what all things need to be taken care inorder the nagios server connect nrpe client without any issues.

In nrpe configuration, do the following

allow_hosts=”nagios server ip”


Allow port 5666 in firewall of nrpe agent

Q37) What is the exit status in nagios custom plugin?

0 – OK, 1 – WARN, 2 – CRITICAL, 3 – UNKNOWN

Q38) How to monitor Asynchronous services via Nagios?

Passive monitoring can be used. Data for monitoring is being collected and stored in to passive poll store from where Nagios can pickup and display.

Q39) What all services can be monitored using Nagios active checks?

SSH, HTTP, FTP, SMTP, Disk Usage, Memory Usage, Network status etc.

Q40) I need to monitor the load average of set of webservers, how can this be achieved?

We need to write a custom plugin script(Bash/Python) which in turn get the status of each and every load average of servers, and then get average of those values.

Q41) How can we get alerts for AWS services using Nagios other than alerts from AWS SNS?

We need to configure aws-cli with required privileges and we have to write custom plugin for the required service to be monitored.

Q42) Suppose if httpd service goes down, how can we automatically start the service using nagios?

We have to create custom Event Handler to achieve this.

Q43) How to write custom plugin in Nagios?

a) Write a bash script in following format.


# Nagios Plugin Bash Script –

# This script checks if program is running

# Check for missing parameters

if [[ -z “$1” ]]

thenecho “Missing parameters! Syntax: ./ service_name”exit 3


if ps ax | grep -v grep | grep $1 > /dev/null

then echo “OK, $SERVICE service is running”exit 0


echo “CRITICAL , $SERVICE service is not running”

exit 2 fi

  1. b) Save the above script in a file and move to the Nagios Plugings Location.
    c) Change permission of the script to 755
    d) Write a command definition in command.cfg
    e) Use this command definition in other service definitions.

Q44) If we need to monitor windows services like disk usage, memory etc, how can we achieve this via Nagios?

We have to install NSClient++ nagios client application in the windows server, then configure it

for allowing required plugins.
; Undocumented key
CheckDisk = enabled
; Undocumented key
CheckSystem = enabled
Test as nagios server side :
/usr/lib/nagios/plugins/check_nt -H HOSTNAME -p 12489 -s PASSWORD -v CPULOAD -l 5,80,90

Q45) What is port 12489 relevant for?

This is NSClient++ client port for monitoring windows servers.

Q46) What is the normal way to provide arguments in nagios nrpe commands.

/usr/local/nagios/libexec/check_nrpe -H nrpe-agent -c check_disk -a ‘-w 20% -c 10%’
Replace nrpe-agent with the server hostname

-c is command to check

-a is for arguments

Q47) We specify $USER1$/check_load in commands.cfg, what is the $USERS1$ ?

USER1 is a macro in nagios which will expand to the plugin location in the command. Nagios supports up to 256 user macros ($USER1$ through $USER256$).
Eg: $USER1$/check_load is /usr/lib64/nagios/plugins/check_load

Q48) What is the difference between HOSTADDRESS and HOSTALIAS macros

HOSTADDRESS is the Address of the host. This value is taken from the address directive in the host definition.

HOSTALIAS is the Long name/description for the host. This value is taken from the alias directive in the host definition.

Q49) What is ocsp_command in nagios?

OCSP is Obsessive Compulsive Service Processor Command which allows you to specify a command to be run after every service check, which can be useful in distributed monitoring. This command is executed after any event handler. or notification commands.

Q50) How to process and store performance data?

  1. Enable the process_performance_data option.
    Example: process_performance_data=1 in Service definition.
    2. Configure Nagios so that performance data is either written to files and/or processed by executing commands.


define command


command_name store-service-perfdata

command_line /bin/echo -e




t$SERVICEOUTPUT$\t$SERVICEPERFDATA$” >> /usr/local/nagios/var/service-perfdata.dat


Q51) What are the reasons for UNKNOWN result all the time?

Nagios is not able to fetch correct data due to
Incorrect command intrepretation.
Intermittent network issues.
Permission issue for executing the command.

Q52) How do we monitor Router or Switches using Nagios?

We have to use SNMP protocol

define service

{use generic-service ; Inherit values from a templatehost_name linksys-srw224pservice_description Port 1 Link Statuscheck_command check_snmp!-C public -o ifOperStatus.1 -r 1 -m RFC1213-MIB


Q53) How to monitor Bandwidth/traffic rate using nagios?

We need to install and use check_mrtgtraf plugin.

define service{

use generic-service ; Inherit values from a template

host_name linksys-srw224p

service_description Port 1 Bandwidth Usage




Q54) Can we achieve distributed monitoring in Nagios?

Yes, via DNX, NSCA, Monit etc plugins are used for distributed monitoring.

Q55) Can we customize charts in nagios for better display and alert it?

Yes, by using different 3rd Party convertor for services like CACTI, RRD, Graphite etc.

Q56) Nagios data is stored in dat format, how do we store in MySQL db for better performance?

We have to install NDOutils and configure Nagios to use it.

Install MySQL and create database for nagios and set username and password.

Install NDOUtils.

Load Schema using ndoutils installdb command.

Change event_broker_options to -1 in nagios.cfg file and broker_module=/usr/lib64/nagios/brokers/ as per installation) config_file=/etc/nagios/ndomod.cfg

Edit ndo2db.cfg and add mysql credentials

Start ndoutils and restart nagios Ref:

Q57) How can we relate nagios with DevOps?

Since DevOps follows agile methodology, continuos monitoring is an integral part of it. This can be achieved using nagios.

Q58) When we use AWS servers for monitoring, how can we automate the monitoring via nagios, as and when the instance is created.

We have to use and automation or configuration management tool to get this task done. Ansible will be best suited to perform this task.

Q59) How to we troubleshooting Nagios core other than host or service monitoring issues?

We have to enable debug mode in nagios.cfg and watch the logs. Which in turn help for find the root cause of the problem.

Q60) How to we enable debug log in Nagios?

Set debug_level=-1 in nagios.cfg

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