Nagios Basics

Introduction

I noticed nagios on the requested topics page. I am far from being an expert with nagios and there is a lot I do not know. I have a working knowledge of most of the basic nagios principles. So, hopefully, I can give a useful introduction and review some one the principles of nagios along the way

Nagios is a network monitoring tool. You define some things for nagios to check, and nagios will alert you if those checks fail.

Nagios has a web UI that is normally used to see the status of the checks. There are some basic administration tasks you can do from the web UI

enabling/disabling notifications

Scheduling Downtime

Forcing immediate checks

Nagios is primarily configured with text files. You have to edit the nagios config files for things like

adding servers

customizing commands

Nagios core vs NagiosXI

NagiosXI is the commercial version of nagios. NagiosXI requires a paid license and includes support. NagiosXI has some extra features including wizards for adding hosts and easy cloning of hosts.

I have used NagiosXI, and personally don't find the extra features very useful. Probably the biggest reason to use NagiosXI is Enterprise that requires commercial support

The community version of nagios is normally referred to as nagios core This episode will focus on the nagios core

Nagios Documentation

I don't like the official nagios core documentation. A lot like man pages, It is a good reference, but can be hard to follow.

Maybe is it possible for someone to read the documentation and be able to install and configure nagios for the first time. But it took me a lot of trial and error to get a functional nagios server following the nagios documentation

Outside of the official documentation, Most of the nagios installation guides I found online recommend downloading and building nagios from the nagios site. My general policy is to use OS provided packages whenever possible. Normally, sticking to packages eases long the term maintenance.

You may not always get the latest feature release, but installation and updates are usually easier. I know not everyone will agree with me here, and will want to build the latest version. Regardless of the install method, most of the nagios principles I go over will still apply

I am making the assumption that most listeners will be most familiar with Debian/Ubuntu, so I will go over installing nagios on Ubuntu using the nagios packages from the Ubuntu repository

Hosts and Services

Before I go over the installation, I'll talk a bit about some of the pieces that make up nagios Nagios checks are for either hosts or services.

From the Nagios documentation

A host definition is used to define a physical server, workstation, device, etc. that resides on your network.

Also from the nagios documentation

A service definition is used to identify a "service" that runs on a host. The term "service" is used very loosely. It can mean an actual service that runs on the host (POP, SMTP, HTTP, etc.) or some other type of metric associated with the host

Normally, hosts are checked using ping. If the host responds to the ping with in the specified time frame, the host is considered up. Once a host is defined and determined to be UP, you can optionally check services on that host

Installation and setup

Install the packages

apt install nagios4

One of the dependencies is the monitoring-plugins I'll talk more about the monitoring-plugins package when we dig in to the