Top Nagios Interview Questions (2024)

1. What is Nagios?

2. Why do we require the Nagios tool?

3. Explain the Nagios architecture?

4. What are Nagios plugins?

5. What is NCPA in Nagios?

6. What is the use of nagios.cfg File in Nagios?

7. How to create a host file inside the server directory of Nagios?

8. How to monitor hosts with Nagios XI by executing monitoring plugins via SSH?

9. How many types of checks are performed on hosts and services in Nagios?

10. What is the protocol used to send passive checks in Nagios?

11. What database does Nagios Core use?

Q: What is Nagios?
Ans:

Nagios is an opensource software monitoring system. The Nagios software performs periodic checks on critical application, network, and server parameters. Nagios, for example, can track memory usage, disk space, microprocessor load, the number of processes currently running, and log files.

Q: Why do we require the Nagios tool?
Ans:

Here are some important factors to use the Nagios monitoring tool:

1. Identifies all types of network or server problems.
2. Assists users in determining the root cause of the problem, allowing users to obtain a permanent solution.
3. Monitoring entire infrastructure and business processes on an ongoing basis.
4. Users can use it to monitor and troubleshoot server performance issues.
5. It enables us to plan for infrastructure upgrades before outdated systems fail.
6. Users could even maintain the service's security and availability.
7. In a crisis mode, automatically resolve problems.

Q: Explain the Nagios architecture?
Ans:

Nagios is built on a client-server model. On a network, a Nagios server is typically running on a host, with plugins running on all remote hosts that should be monitored.

1. The scheduler is a part of the Nagios server. This sends a signal to the remote host to run the plugins.
2. The plugin obtains the status from the remote host.
3. The plugin transfers the information to the process scheduler.
4. The process scheduler updates the GUI, as well as notifications are being sent to admins.

Q: What are Nagios plugins?
Ans:

Nagios Plugins are stand-alone extensions to Nagios Core which allow Core to monitor almost anything. Plugins process command-line arguments, run a specific check, and then report the results to Nagios Core.
Plugins make users use Nagios to monitor hosts, devices, services, protocols, and applications.

Q: What is NCPA in Nagios?
Ans:

NCPA is an acronym for Nagios Cross Platform Agent. Nagios Core has a plug-in that could be downloaded. Although using Nagios XI is not required for this agent, it does come with a wizard for creating active checks with NCPA.

Q: What is the use of nagios.cfg File in Nagios?
Ans:

This is the main Nagios core configuration file. This file specifies the location of the Nagios log file, the hosts and services state update interval, the lock file, and the status.dat file. This file defines the Nagios users and groups for which the instances are running. It contains the paths to all of the individual object configuration files such as commands, contacts, templates, and so on.

Q: What is NRPE (Nagios Remote Plugin Executor)?
Ans:

The NRPE, or Nagios remote plugin executor help to be run on remote Linux or UNIX workstations. These plugins are used to monitor CPU load and memory utilisation on remote machines as if they were local resources. It is necessary since this information is rarely accessible publicly to an external machine, and the NRPE agent is installed on remote devices for this purpose.

The NRPE add-on or plugin consists of two parts that work together to complete the task:

1. The check_nrpe plugin is a local machine plugin that is used for monitoring.
2. The NRPE daemon, which can be run on remote machines.

Q: How to create a host file inside the server directory of Nagios?
Ans:

You can create a host file in the Nagios server directory that includes the host and service definitions as given below:

sudo gedit /usr/local/nagios/etc/servers/ubuntu_host.cfg

Host configuration file

define host {
   use linux-server
   host_name ubuntu_host
   alias Ubuntu Host
   address 192.168.1.10
   register 1
}
define service {
   host_name ubuntu_host
   service_description PING
   check_command check_ping!100.0,20%!500.0,60%
   max_check_attempts 2
   check_interval 2
   retry_interval 2
   check_period 24x7
   check_freshness 1
   contact_groups admins
   notification_interval 2
   notification_period 24x7
   notifications_enabled 1
   register 1
}

Q: How to monitor hosts with Nagios XI by executing monitoring plugins via SSH?
Ans:

SSH is a secure communication protocol which can be used to log in to and/or execute commands on remote servers.

Nagios XI could monitor metrics and services on remote machines by utilising the check by check_by_ssh plugin. The check_by_ssh plugin enables Nagios to securely execute monitoring plugins and scripts on remote machines without requiring authentication credentials.

Check by ssh requires the following installation/configuration on the remote Linux/Unix server.

1. Create a nagios user
2. Install Nagios plugins and/or monitoring scripts
3. Set up and configure the SSH daemon

Now run the check_by_ssh command:

/usr/local/nagios/libexec/check_by_ssh -H remoteip -C uptime

Your remote server's output should look something like this if everything is set up correctly:

13:01:35 up 20 min, 1 user, load average: 0.00, 0.02, 0.04

Q: How many types of checks are performed on hosts and services in Nagios?
Ans:

While checking hosts and services in Nagios, there are two types of checks performed.

1. Active Checks

   Active checks are initiated by the Nagios process and execute on a regularly scheduled basis after they are started. Nagios executes plugins and passes the information about what needs to be checked in order to monitor remote hosts and services.

2. Passive Checks

   Passive checks are initiated and performed by external applications/processes. Passive check results are then submitted to Nagios for further processing The main difference between active and passive checks is that active checks are initiated and performed by Nagios, whereas passive checks are performed by external applications.

Q: What is the protocol used to send passive checks in Nagios?
Ans:

We could use the NSCA or NRDP addons to allow remote hosts to send passive check results to the monitoring host. The NSCA addon is made up of two parts: a daemon that runs on Nagios Core hosts and a client that runs on remote hosts.

Q: What database does Nagios Core use?
Ans:

By default, Nagios Core does not utilizes any database , however the NCPA agent uses a SQLite database.