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How to Setup a Nagios Monitoring Server

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Good old nagios! Nagios is a great Open Source Monitoring Server that monitors your servers and services/applications that is hosted on top of them, and has the ability to notify in the event when they go down.

I've been using Nagios for the last 7 years and worked for 3 business that chose Nagios as their preferred server monitoring solution.

All Nagios related posts are grouped under the #nagios category.

What we are doing today

Today we will setup a Nagios server and its plugins. The plugins helps to check different endpoints, such as custom tcp checks, ssh, snmp etc.

In this nagios tutorial series, I will publish a couple of post which will include:

  • Setup the Nagios Server and its Plugins - this post
  • Setup the NRPE Server and NRPE Client Server (this is nice for local ports or custom checks)
  • Setup Nagiosgraph (Graph performance data and add it as extra host configuration)
  • Setup a custom Bash and Python Nagios Plugin for Custom Checks
  • Setup a Telegram / Slack Plugin

Installing Dependencies:

Go ahead and install all the dependencies needed by nagios and add the nagios user and group:

$ apt update
$ apt install build-essential libgd-dev openssl libssl-dev unzip apache2 -y
$ apt install autoconf gcc libc6 make wget unzip apache2 php libapache2-mod-php7.2 libgd-dev
$ apt install libmcrypt-dev libssl-dev bc gawk dc build-essential libnet-snmp-perl gettext
$ apt install libcarp-clan-perl rrdtool php-rrd libssl1.0-dev
$ useradd nagios
$ groupadd nagcmd
$ usermod -a -G nagcmd nagios

Install Nagios

Download the nagios tarball from their website, have a look at https://www.nagios.org/downloads/ for the latest version.

$ wget -O nagios.tar.gz 'https://assets.nagios.com/downloads/nagioscore/releases/nagios-4.4.3.tar.gz?__hstc=118811158.7bdae752f04b6d927ddf150ae1ce5c71.1552389135285.1552394646569.1552410974898.3&__hssc=118811158.1.1552410974898&__hsfp=2323916385#_ga=2.246938692.1332751653.1552389134-913645931.1552389134'

Extract the archive:

$ tar xpf nagios*.tar.gz
$ cd nagios-4.4.3/

Configure with nagios user and nagcmd group, install and change the ownership of the generated data:

$ ./configure --with-nagios-group=nagios --with-command-group=nagcmd
$ make -j4 all
$ make install
$ make install-commandmode
$ make install-init
$ make install-config
$ /usr/bin/install -c -m 644 sample-config/httpd.conf /etc/apache2/sites-available/nagios.conf
$ usermod -a -G nagcmd www-data

Install Nagios Plugins

Get the nagios plugins tarball, extract and install:

$ wget nagios-plugins.tar.gz 'https://nagios-plugins.org/download/nagios-plugins-2.2.1.tar.gz#_ga=2.250909126.1332751653.1552389134-913645931.1552389134'
$ tar xpf nagios-plugins*.tar.gz
$ cd nagios-plugins-2.2.1
$ ./configure --with-nagios-user=nagios --with-nagios-group=nagcmd --with-openssl
$ make -j4
$ make install

Access Nagios

Enable apache modules:

$ a2enmod rewrite
$ a2enmod cgi

Setup basic auth for logging onto nagios:

$ htpasswd -c /usr/local/nagios/etc/htpasswd.users nagiosadmin

Setup a symlink for apache's nagios configuration

The configuration for the above will look more or less like the following:

$ cat /etc/apache2/sites-enabled/nagios.conf

...
         Require all granted
         AuthName "Nagios Access"
         AuthType Basic
         AuthUserFile /usr/local/nagios/etc/htpasswd.users
         Require valid-user
...

Create the systemd unit file for nagios /etc/systemd/system/nagios.service

[Unit]
Description=Nagios
BindTo=network.target

[Install]
WantedBy=multi-user.target

[Service]
Type=simple
User=nagios
Group=nagcmd
ExecStart=/usr/local/nagios/bin/nagios /usr/local/nagios/etc/nagios.cfg

Reload the daemon:

$ systemctl daemon-reload

Enable the service:

$ systemctl enable /etc/systemd/system/nagios.service

Ensure nagios is started:

$ systemctl restart nagios
$ systemctl restart apache2

Access nagios on http://nagios-ip/nagios with the credentials that you configured earlier.

Up Next

In the next posts I will cover the following:

  1. Setup NagiosGraph for monitoring performance data
  2. Show you how to create a custom nagios plugin in python
  3. Create a Custom Notification service to send notifications to Telegram (or any API)

Thank You

Thanks for reading, if you like my content, feel free to check out my website, and subscribe to my newsletter or follow me at @ruanbekker on Twitter.

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