25+Questions For Your Nagios Interview

Are you preparing for a DevOps interview? Then you should read these Nagios interview questions and answers. 

Nagios is the most popular continuous monitoring software among companies. Companies rely on constant monitoring software to highlight errors and solve problems before they become significant issues. As a DevOps professional, recruiters would expect you to be familiar with all aspects of this powerful software. We’ve compiled a list of the most important Nagios interview questions and answers to help you prepare for your job interview. Feel free to share this list with others. 

What is Nagios?

Nagios is a popular open-source solution that helps in monitoring systems, networks, and applications. It’s a standard DevOps tool, which tracks all the changes taking place in the subject. In case a technical fault arises, it can send alerts to the staff and make them aware of the issue as well. This way, the problem can be solved faster and earlier without it becoming a significant issue. 

Nagios provides a centralized view of the complete infrastructure and vies detailed information on its status as well. You can also mention how it benefits organizations and how you can use it to solve the numerous problems related to the specific organization.

Nagios helps in understanding where the infrastructure lacks and how you can upgrade it to overcome those problems. You can also mention how it automatically solves the issues detected. Nagios enables you to monitor the whole organization, its infrastructure, and its various processes. 

This should answer the question. But you can add more points such as the advantages of using Nagios, and some other applications of Nagios, if required. 

How Nagios helps DevOps Professionals?

Nagios helps DevOps problems in tracking down issues and solving them in their early stages. This software solution overlooks every aspect of the infrastructure so it can spot an error and alert the technical team quickly. This way, DevOps professionals don’t have to worry about monitoring the systems for finding problems. They can rely on Nagios to spot the same. 

What are the features of Nagios?

Nagios has many features. 

– Its APIs enable it for monitoring various systems, infrastructures, and applications.

– It has add-ons that make you aware of the aging infrastructure and help you in planning upgrades.

– You have full access to its code as it is open-source software. 

– Its reporting system is fast and agile. It gives you a record of all the alerts and their responses. 

– You can view the entire infrastructure of your organization through Nagios while also seeing the detailed information about everything.

– Nagios has a vast community of more than a million users. If you come across any problems or have any questions, you can ask them who’d be happy to help. 

How does Nagios operate?

You can give this explanation as to your answer:

  • Nagios runs as a service on a server
  • It runs plugins on the server which connect with hosts on the network
  • You can see the detailed information of the connected host through its interface
  • In case some issue arises, you would receive an email or another notification
  • Nagios runs scripts at specific times and saves the results of those scripts
  • If the results of running the scripts change, Nagios starts running other scripts

 That is how Nagios operates. 

What do you mean by ‘Plugins’ in Nagios?

Plugins in Nagios are different scripts that check the status of a service or host. You’d run them from the command line. Nagios checks the results from its plugins to see the condition of the various hosts and services present in your network. 

You can also explain why plugins are necessary for Nagios. 

Nagios requires plugins to check the status of the numerous hosts and services present in a network. A plugin verifies the required host and sends the results of its check to Nagios. Nagios then processes the results and determines whether an action is needed or not. 

What is NRPE?

NRPE enables you to run plugins on remote Unix and Linux machines. This way, Nagios can monitor local resources such as memory usage and CPU on remote components. Typically, these resources are not given to remote machines; that’s why you’d need to use NRPE. 

You can also give an explanation of NRPE architecture for a more detailed answer. 

NRPE contains two sections, the NRPE daemon, and the check_NRPE plugin. The former runs on a different computer while the latter remains in the local machine and has an SSL connection between the monitoring machine and the remote machine. 

What is a Passive Check? 

In Nagios, external processes initiate Passive checks. When they are completed, the results are sent to Nagios. Passive checks help in monitoring asynchronous services. Those services can’t be tracked without regular polling of their status. Passive checks also help Nagios in checking the status of hosts that are behind a firewall as they can’t be verified through a monitoring host. 

What are the advantages of using Nagios?

Nagios offers plenty of advantages to an organization. 

  • It allows you to plan future upgrades for your existing infrastructure
  • It ensures a technical error in your IT infrastructure has minimum impact
  • It quickly alerts you of any new problems
  • It allows you to monitor the entire system and infrastructure 
  • It coordinates the responses of the technical staff
  • It helps you find out how fast your team responds to technical problems
  • It ensures that SLAs (Service-Level Agreements) of your organization are met

What is Icinga? How is it related to Nagios?

Icinga is another popular open-source software that helps in monitoring services. It was designed in 2009 to help Nagios, but it has become a separate software. 

What is an Active Check?

Nagios performs an Active check to poll a device or service for its status information on a scheduled basis. 

Can you name a few databases which support Nagios?

Many databases support Nagios. They are Oracle, Postgres, Microsoft SQL solutions, and MySQL. 

What is Nagios XI?

Nagios is the most trusted and most powerful monitoring software. It can help you in monitoring applications, network protocols, systems, services, and metrics. It provides you with all the advantages of Nagios (discussed above) and has a powerful performance. 

Is Nagios used to monitor window machines?

Yes, Nagios is used to monitor window machines. You can do so by setting-up Nagios for monitoring the required window system and then add a separate server and host for performing the task. 

What is OID Nagios?

The Simple Network Management Protocol (aka SNMP) uses Object Identifiers for defining the Management Information Base. 

What is the Nagios Network Analyzer?

The network analyzer is a vital component of Nagios which checks the system for potential dangers. Its quick scan enables the admin to get the required data about the health of the system. 

What are the benefits of using Nagios to monitor websites?

Nagios can help you monitor websites too. It improves the website’s availability, helps you spot bugs, and you can enhance your site’s performance and avoid online security threats as well with the help of Nagios. 

Is Nagios Object-oriented? If so, can you elaborate on what it means?

Object-oriented means that you can produce object definitions in Nagios that are inherited from other objects. As Nagios is object-oriented, its relationship with its components remains simple without any intricate details. 

Which protocols support Nagios?

SMTP Monitoring, POP Monitoring, FTP Monitoring, IPMI Monitoring, DNS Monitoring, and LDAP Monitoring are some of the protocols Nagios supports. 

Can you use Nagios for Cloud Monitoring?

Yes, you can use Nagios for cloud monitoring. It is one of the most popular monitoring tools available in the market. 

What are objects in Nagios?

All elements related to the alerting logic and the monitoring process are objects in Nagios. 

Name three virtualization platforms that support Nagios.

Microsoft Virtual PC, Amazon EC2, and VMware are three of the most popular virtualization platforms supporting Nagios. 

What are the object types in Nagios?

Nagios has a variety of object types such as host groups, periods, services, hosts, contact, notifications, and commands. 

What are the two-state types in Nagios?

Soft states and hard states are the two primary state types in Nagios. 

Which database format does Nagios support for storing data?

Nagios supports the RRD database format for storing status data. 

What are the sections of NDO utilities?

NDO utilities include FILE2STOCK Utility, NDOMOD Event Broker Module, NDO2DB Daemon, and LOG2NDO Utility. 

What are the default credentials in Nagios?

The Username and Password are “nagiosadmin” in Nagios as default. 

What language does Nagios core use?

Nagios core uses PHP and CGI. 

What are the required conditions for Nagios to check external commands?

Nagios checks for external commands regularly according to the command_check_interval option. In addition to the regular checks, it also checks for external commands when an event handler is executed. 

What are the differences between Passive and Active checks?

It is one of the most popular Nagios interview questions, so we suggest you prepare the answer thoroughly. 

The main difference between Active checks and Passive checks is that Nagios performs the former while an external application performs the latter. 

Passive checks monitor services that are located behind a firewall or are asynchronous. Active tests can’t be done on those services or hosts even though Nagios performs them regularly. 

How is Nagios related to DevOps?

Continuous monitoring is a core component of DevOps and Nagios is a popular tool for the same. 

Can you customize charts in Nagios?

Yes, you can customize charts through a third-party tool such as Graphite or CACTI.

What is the difference between soft and hard states in Nagios?

To answer this question, you should define both of these states. 

When the results of a host or service are not OK, but it has not been rechecked multiple times according to max_check_attempts, then the error is specified as a Soft error. When a host or service recovers from a Soft Error, it is called Soft Recovery.

On the other hand, when the results of a host or service check are not OK even when they have been rechecked several times, according to max_check_attempts, the error is called Hard Error. Recovery from such a kind of error is called Hard Recovery. 

Which three variables affect inheritance and recursion in Nagios?

The three variables affecting recursion and inheritance are Name, Use, and Register. The name is a placeholder for other objects. Use specifies the parent object and Register can either have a value of 1 or 0. If the Register has a value of 1, it means it’s an actual object. If it has a value of 0, it means the object is only a template and isn’t a real object. 

What is meant by State Stalking?

Let us discuss what State Stalking is. State stalking helps in logging. With State Stalking, Nagios watches a particular service or host and log any changes it notices in the check results. You can also add that State Stalking is quite helpful in the analysis of logs. Without State Stalking, Nagios logs a check only when the state is changed between two checks. 

What is Flap Detection in Nagios?

When a host or service changes its state too frequently, it is called Flapping. Flapping can lead to many problems, which could, in turn, cause many recovery notifications to arise. Nagios checks if a service or host has started flapping during its status check. 

Nagios checks for flapping. It does so by storing the results of the previous 21 checks of the specific service or host first. And it analyzes those results to see how frequent state changes occurred. It determines a percent state change value through that data and compares the same to flapping thresholds. When the percent state change is greater than the high threshold for flapping, the object is said to have started flapping. And when the percent state change is lower than the low threshold for flapping the object is said to have stopped flapping. 

How would you explain the ‘Machine is Unreachable’ error?

When Nagios fails in finding a path to a specific node, it shows this error. The node might be up, but because Nagios can’t access it, it shows the node as unreachable. 

Final Thoughts

We hope you found these Nagios interview questions helpful. Be sure to prepare all these questions thoroughly. 

If you’re interested to learn more about Nagios, check out upGrad & IIIT-B’s PG Diploma in Full-stack Software Development which is designed for working professionals and offers 500+ hours of rigorous training, 9+ projects, and assignments, IIIT-B Alumni status, practical hands-on capstone projects & job assistance with top firms.

 

Arjun Mathur

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