Top 100+ Nagios Admin Interview Questions And Answers

Question 1. What Are Plugins In Nagios?

Answer :

Plugins are scripts (Perl scripts, Shell scripts, and so forth.) which could run from a command line to test the fame of a host or carrier. Nagios uses the outcomes from the plugins to determine the modern-day repute of hosts and services on your community.

Once you have described Plugins I will recommend you to explain why we want plugins.

Nagios will execute a Plugin whenever there's a need to test the popularity of a host or carrier. The plugin will carry out the test after which surely returns the result to Nagios. Nagios will process the effects that it gets from the Plugin and take the essential moves.

Question 2. What Is Nagios And How It Works ?

Answer :

Nagios is an open supply System and Network Monitoring utility. Nagios runs on a server, generally as a daemon or service. Nagios periodically run plugins to screen clients, if it found whatever caution and essential it will ship an alerts through Email OR SMS as consistent with the configuration.

The Nagios daemon behaves like a scheduler that runs sure scripts at positive moments. It stores the consequences of these scripts and will run different scripts if these effects change.

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Question 3. What Are Ports Numbers Nagios Will Use To Monitor Clients?

Answer :

Port numbers are 5666, 5667 and 5668

Question four. Explain Main Configuration File And Its Location?

Answer :

Resource File : It is used to store sensitive statistics like username, passwords without making them to be had to the CGIs. Default path: /usr/local/nagios/and so forth/aid.Cfg
Object Definition Files: It is the vicinity have been you define all you need to monitor and the way you need to display. It is used to define hosts, services, hostgroups, contacts, contact agencies, instructions, and so on.. Default Path:/usr/neighborhood/nagios/etc/gadgets/
CGI Configuration File : The CGI configuration document consists of some of directives that have an effect on the operation of the CGIs. It also incorporates a reference the main configuration file, so the CGIs recognise the way you’ve configured Nagios and wherein your item definitions are stored. Default Path: /usr/neighborhood/nagios/sbin/
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Question five. Nagios Administrator Is Adding a hundred+ Clients In Monitoring But He Don’t Want To Add Every .Cfg File Entry In Nagios.Cfg File He Want To Enable A Directory Path. How Can He Configure Directory For All Configuration Files?

Answer :

He can able to achieve the above state of affairs by means of including the directory course in nagios.Cfg report, in line quantity fifty four we should upload beneath line.

Fifty four  cfg_dir=/usr/local/nagios/etc/gadgets/monitor

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Question 6. What Is Nagios?

Answer :

Nagios is one of the tracking tools. It is used for Continuous monitoring of structures, applications, services, and enterprise approaches and many others. In a DevOps lifestyle. In the event of a failure, Nagios can alert technical body of workers of the hassle, allowing them to start remediation techniques before outages influences business processes, quit-customers, or customers. With Nagios you don’t ought to give an explanation for why an unseen infrastructure outage affect your agency’s bottom line.

 

Question 7. Now, Once You Have Defined What Is Nagios, You Can Mention The Various Things That You Can Achieve Using Nagios?

Answer :

By the use of Nagios you could:

• Plan for infrastructure improvements before old structures purpose disasters.

• Respond to troubles at the first sign of a problem.

• Automatically repair issues whilst they're detected.

• Coordinate technical crew responses.

• Ensure your corporation’s SLAs are being met.

• Ensure IT infrastructure outages have a minimal effect on your organization’s backside line.

• Monitor your complete infrastructure and commercial enterprise approaches. 

This usual completes the answer to this question. The further information like blessings etc. Can be added as per the path in which the dialogue is heading.

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Question 8. Explain Nagios State Types?

Answer :

The repute of provider or host i.E. OK, WARNING, UP, DOWN and many others..
The sort of nation the carrier or host is in.
There are  forms of states SOFT states and HARD states.
Question nine. Explain What Is Soft And Hard States?

Answer :

When a provider or host take a look at results are in a non-OK or non-UP country and the carrier test has not yet been rechecked the wide variety of instances designated via the max_check_attempts directives inside the carrier or host definition. This is known as Soft Error. When a provider or a number recovers from Soft Error this is taken into consideration as Soft Recovery.
When a service or host take a look at results are in a non-OK or non-UP state and the provider check has been rechecked the variety of instances specific with the aid of the max_check_attempts directives within the provider or host definition. This is known as Hard Error. When a provider or a number recovers from Hard Error that is taken into consideration as Hard Recovery.
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Question 10. Nagios Says My Machine Is Unreachable, Not Down. What Is The Difference And How It Is Achieved?

Answer :

When Nagios says a node is unreachable, a node is unreachable if Nagios is not able to discover a path to the node. 
Now you could mention the difference.

The node itself can be up but due to the fact Nagios is not able to connect to it, it has to mark this as unreachable. To acquire this, Nagios use parent-infant dating between components.

Finally for better information give an explanation for it with an example.

A router may be described as a discern for a server.
Now Nagios exams for server and marks it as down.
It then tests the determine (in our example, the router)
If determine is likewise down, then server is marked as unreachable.
If Parent is up, the server is marked as clearly down.
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Question 11. What Is State Stalking In Nagios?

Answer :

State Stalking is used for logging purposes. When Stalking is enabled for a particular host or provider, Nagios will watch that host or carrier very cautiously and log any adjustments it sees inside the output of test effects.

Depending on the dialogue among you and interviewer you can additionally add:

It can be very beneficial in later analysis of the log documents. Under normal occasions, the result of a bunch or carrier test is simplest logged if the host or service has changed nation since it was final checked. 

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Question 12. What Is Meant By Saying Nagios Is Object Oriented?

Answer :

One of the functions of Nagios is object configuration layout in that you could create object definitions that inherit residences from other object definitions and as a result the name. This simplifies and clarifies relationships between numerous components.

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Question thirteen. What Are The Three Main Variables That Affect Recursion And Inheritance In Nagios?

Answer :

First call the variables and then a small rationalization of every of these variables: 

Name
Use
Register
Now I will provide a small reason for each of those variables.

Name is a placeholder this is used by other items. Use defines the “figure” item whose residences must be used. Register could have a cost of zero (indicating its best a template) and 1 (an real item). The sign up value is by no means inherited.

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Question 14. Explain How Flap Detection Works In Nagios?

Answer :

Flapping happens when a provider or host modifications state too frequently, this causes lot of problem and recovery notifications.

Once you have got described Flapping explain how Nagios detects Flapping.

Whenever Nagios checks the status of a bunch or provider, it's going to test to see if it has commenced or stopped flapping. Nagios follow the beneath method to try this:

Storing the outcomes of the ultimate 21 checks of the host or provider studying the ancient check consequences and decide where nation modifications/transitions arise.
Using the state transitions to decide a percent kingdom change value (a measure of change) for the host or service.
Comparing the percent state exchange fee in opposition to low and high flapping thresholds
A host or provider is decided to have started out flapping when its percent kingdom trade first exceeds a high flapping threshold.
A host or carrier is decided to have stopped flapping while its percentage state goes beneath a low flapping threshold.
Question 15. Explain Main Configuration File Of Nagios And Its Location?

Answer :

The foremost configuration report contains some of directives that affect how the Nagios daemon operates. This config record is examine by means of both the Nagios daemon and the CGIs (It specifies the vicinity of your important configuration document).

Now you can tell wherein it is gift and the way it's far created.

A sample predominant configuration record is created in the base listing of the Nagios distribution when you run the configure script. The default name of the principle configuration record is nagios.Cfg, it's also placed in the etc/ subdirectory of you Nagios set up (i.E. /usr/local/nagios/and so forth/).

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Question sixteen. How Does Nagios Help With Distributed Monitoring?

Answer :

With Nagios you could reveal your complete employer by means of using a allotted monitoring scheme in which local slave times of Nagios perform tracking obligations and document the consequences returned to a unmarried master. You control all configuration, notification, and reporting from the grasp, even as the slaves do all the paintings. This layout takes advantage of Nagios’s potential to utilize passive assessments i.E. Outside programs or processes that ship results lower back to Nagios. In a disbursed configuration, these outside packages are other times of Nagios.

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Question 17. What Is The Difference Between Active And Passive Check In Nagios?

Answer :

The important distinction among Active and Passive tests is that Active tests are initiated and done by Nagios, whilst passive tests are completed by way of external applications.

Passive checks are beneficial for tracking offerings which are:

Asynchronous in nature and can not be monitored successfully by using polling their fame on a often scheduled basis.
Located behind a firewall and can't be checked actively from the monitoring host.
The predominant functions of Actives assessments are as follows:
Active assessments are initiated by way of the Nagios process.
Active checks are run on a regularly scheduled foundation.
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Question 18. When Does Nagios Check For External Commands?

Answer :

Nagios take a look at for external commands beneath the subsequent situations:

At regular durations exact via the command_check_interval alternative in the fundamental configuration report or,
Immediately after occasion handlers are completed. This is further to the everyday cycle of external command assessments and is carried out to provide instantaneous action if an event handler submits instructions to Nagios.
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Question 19. What Do You Mean By Passive Check In Nagios?

Answer :

Passive checks are initiated and executed by means of outside packages/tactics and the Passive check results are submitted to Nagios for processing.

 

Question 20. Explain The Need For Passive Check?

Answer :

Passive checks are useful for monitoring services which can be Asynchronous in nature and cannot be monitored correctly by way of polling their fame on a regularly scheduled foundation. It can also be used for monitoring offerings which are Located at the back of a firewall and can't be checked actively from the monitoring host.

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Question 21. What Is Meant By Nagios Backend?(unable To Find A Relevant Explanation)

Answer :

Both Configuration and Logs may be stored in a backend. Configurations are saved in backend the use of NagiosQL. Historical statistics are saved the use of ndoutils. In addition, you also have nagdb and opdb.

Question 22. What Is Database Is Used By Nagios To Store Collected Status Data?

Answer :

Nagios core will use default RRD database layout to store status records

Question 23. What Are The Operating Systems We Can Monitor Using Nagios..?

Answer :

Any Operating System We can monitor the use of Nagios, OS ought to aid to put in Nagios Clinet either SNMP.

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Question 24. What Are The Components That Make Up The Ndo Utilities ?

Answer :

There are four predominant additives that make up the NDO utilities:

NDOMOD Event Broker Module : The NDO utilities consists of a Nagios event dealer module (NDOMOD.O) that exports information from the Nagios daemon.Once the module has been loaded by the Nagios daemon, itcan get entry to all of the information and good judgment present inside the strolling Nagios process.The NDOMOD module has been designed to export configuration records, as well as records approximately numerous run time occasions that arise within the monitoring method, from the Nagios daemon. The module can ship this records to a trendy document, a Unix domain socket, or a TCP socket.
LOG2NDO Utility : The LOG2NDO application has been designed to permit you to import ancient Nagios and NetSaint log files right into a database via the NDO2DB daemon (described later). The utility works through sending historical log record facts to a popular document, a Unix domain socket, or a TCP socket in a format the NDO2DB daemon knows. The NDO2DB daemon can then be used to method that output and shop the historical log report  statistics in a database.
FILE2SOCK Utility :  The FILE2SOCK software is quite easy. Its reads enter from a preferred record (or STDIN) and writes all of that facts to both a Unix domain socket or TCP socket. The facts this is examine isn't always processed in any manner earlier than it's far despatched to the socket.
NDO2DB Daemon:   The NDO2DB software is designed to take the records output from the NDOMOD and LOG2NDO additives and keep it in a MySQL or PostgreSQL database.When it starts offevolved, the NDO2DB daemon creates both a TCP or Unix area socket and waits for customers to attach. NDO2DB can run both as a standalone, multi-method daemon or underneath INETD (if the usage of a TCP socket). Multiple clients can connect to the NDO2DB daemon’s socket and transmit facts concurrently. A separate NDO2DB manner is spawned to address each new client that connects. Data is read from each patron and saved in a consumer-specific database for later retrieval and processing.
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Question 25. What Is Ndoutils ?

Answer :

The NDOUTILS addon is designed to keep all configuration and occasion information from Nagios in a database. Storing data from Nagios in a database will allow for faster retrieval and processing of that statistics and could assist serve as a basis for the improvement of a new PHP-primarily based web interface in Nagios four.1.

MySQL databases are presently supported by way of the addon and PostgreSQL assist is in development.

The NDOUTILS addon changed into designed to work for customers who've:

Single Nagios installations
Multiple standalone or “vanilla” Nagios installations
Multiple Nagios installations in distributed, redundant, and/or failover environments.
Each Nagios method, whether or not it's miles a standalone monitoring server or a part of a distributed, redundant, or failover tracking setup, is called an “instance”. In order to keep the integrity of stored facts, each Nagios example need to be labeled with a unique identifier or name.

Question 26. What Is Nrpe?

Answer :

The Nagios Remote Plugin Executor addon is designed to can help you execute Nagios plugins on far off Linux/Unix machines. The primary 
reason for doing this is to permit Nagios to screen “local” sources (like CPU load, memory utilization, and many others.) on remote machines. Since those public resources are not typically exposed to external machines, an agent like NRPE have to be mounted on the far off Linux/Unix machines.

The NRPE addon consists of two portions:

The check_nrpe plugin, which resides on the local tracking system
The NRPE daemon, which runs at the far flung Linux/Unix system
When Nagios desires to screen a useful resource of carrier from a remote Linux/Unix machine:

Nagios will execute the check_nrpe plugin and inform it what carrier wishes to be checked
The check_nrpe plugin contacts the NRPE daemon at the far flung host over an (optionally) SSL-protected connection
The NRPE daemon runs the best Nagios plugin to check the carrier or resource
The outcomes from the service test are surpassed from the NRPE daemon back to the check_nrpe plugin, which then returns the check effects to the Nagios method.
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Question 27. Explain Distributed Monitoring ?

Answer :

Nagios may be configured to aid allotted tracking of community services and sources.

When putting in place a allotted tracking surroundings with Nagios, there are variations inside the manner the relevant and distributed servers are configured.

The characteristic of a distributed server is to actively perform exams all of the offerings you define for a “cluster” of hosts. It essentially just imply an arbitrary institution of hosts on your community. Depending on your community format, you may have numerous clusters at one physical place, or each cluster can be separated by a WAN, its personal firewall, and so forth. There is one allotted server that runs Nagios and video display units the offerings at the hosts in every cluster. A dispensed server is usually a bare-bones set up of Nagios. It doesn’t have to have the web interface established, ship out notifications, run occasion handler scripts, or do some thing aside from execute provider checks if you don’t need it to.

The purpose of the principal server is to genuinely pay attention for carrier test consequences from one or more disbursed servers. Even although services are now and again actively checked from the relevant server, the energetic tests are simplest accomplished in dire instances.

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Question 28. Explain How Flap Detection Works In Nagios?

Answer :

Nagios supports non-compulsory detection of hosts and services that are “flapping”. Flapping occurs while a carrier or host modifications state too regularly, resulting in a hurricane of hassle and restoration notifications. Flapping can be indicative of configuration troubles (i.E. Thresholds set too low), troublesome offerings, or actual community issues.

Whenever Nagios tests the status of a bunch or carrier, it'll take a look at to look if it has began or stopped flapping. It does this with the aid of:

Storing the effects of the last 21 exams of the host or ser vice
Analyzing the ancient test results and decide where country modifications/transitions occur
Using the state transitions to decide a percent country trade value (a measure of exchange) for the host or service
Comparing the percent country change fee towards low and high flapping thresholds
A host or carrier is determined to have commenced flapping when its percent country change first exceeds a excessive flapping threshold.
A host or carrier is decided to have stopped flapping when its percent nation is going below a low flapping threshold (assuming this is become formerly flapping).
The ancient provider test effects are tested to determine in which kingdom adjustments/transitions occur. State changes occur while an archived nation is different from the archived kingdom that without delay precedes it chronologically. Since we maintain the outcomes of the final 21 service assessments in the array, there may be a opportunity of having at maximum 20 state modifications. 
The flap detection good judgment uses the kingdom modifications to determine an general percentage state alternate for the carrier. This is a degree of volatility/change for the service. Services that in no way change state could have a zero% kingdom trade fee, whilst services that change nation on every occasion they’re checked could have a hundred% kingdom change. Most offerings will have a percent state exchange someplace in between.

Question 29. What Is State Stalking?

Answer :

Stalking is purely for logging functions.When stalking is enabled for a particular host or carrier, Nagios will watch that host or provider very cautiously and log any adjustments it sees in the output of take a look at results. As you’ll see, it is able to be very helpful to you in later analysis of the log files. Under regular situations, the result of a bunch or service test is most effective logged if the host or carrier has modified country because it became final checked. There are a few exceptions to this, but for the maximum component, that’s the rule.

If you enable stalking for one or extra states of a specific host or carrier, Nagios will log the outcomes of the host or carrier test if the output from the check differs from the output from the previous test.

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Question 30. What Is The Difference Between Nagiosxi And Nagios Core?

Answer :

NagiosXI is a Paid model and Nagios middle is a unfastened version.

NagiosXI consists of lot of functions which we can modify using net interface. Nagios Core default not include all the features we should put in force via putting in plugins.

Question 31. How To Generate Performance Graphs?

Answer :

In Nagios Core there is no inbuilt choice to generate the overall performance graphs, We should install pnp4nagios and upload hosts and offerings URL’s in defination documents.

Question 32. How Do I Use Plugin X?

Answer :

 We must download the plugins from nagios trade https://exchange.Nagios.Org/. Then test the nagios plugin by walking manually.

Most all plugins will show simple utilization records while you execute them using ‘-h’ or ‘–help’ on the command line.

Question 33. What Are Objects?

Answer :

Objects are all of the elements which can be concerned inside the tracking and notification common sense.

Types of gadgets include:

Services  are one of the vital gadgets in the monitoring good judgment. Services are associated with hosts Attributes of a bunch (CPU load, disk usage, uptime, and many others.)
Service Groups :are organizations of one or greater offerings. Service corporations could make it less difficult to (1) view the fame of related services inside the Nagios web interface and (2) simplify your configuration through using object hints.
Hosts  are one of the vital gadgets within the tracking common sense.Hosts are generally physical devices to your network (servers, workstations, routers, switches, printers, etc).
Host Groups   are organizations of one or greater hosts. Host organizations can make it easier to (1) view the status of associated hosts inside the Nagios web interface and (2) simplify your configuration via the use of object tricks
Contacts Conact facts of  human beings worried within the notification system
Contact Groups are groups of one or more contacts. Contact businesses can make it simpler to define all the folks who get notified when certain host or carrier problems arise.
Commands are used to inform Nagios what programs, scripts, and so forth. It ought to execute to perform ,Host and service exams and when Notifications must send and so on.
Time Periods are are used to manipulate ,When hosts and services can be monitored
Notification Escalations Use for escalating the the notification.
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Question 34. How To Verify Nagios Configuration?

Answer :

In order to confirm your configuration, run Nagios with the -v command line option like so:

/usr/neighborhood/nagios/bin/nagios -v /usr/local/nagios/and so on/nagios.Cfg

If you’ve forgotten to enter some crucial records or misconfigured matters, Nagios will spit out a caution or blunders message that should factor you to the vicinity of the hassle. Error messages generally print out the line within the configuration document that appears to be the source of the trouble. On mistakes, Nagios will often go out the pre-flight test and go back to the command prompt after printing most effective the first errors that it has encountered.