How to Install Nagios Server Monitoring on Ubuntu 16.04

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Nagios is an open source software for system and network monitoring. Nagios can monitor the activity of a host and its services, and provides a warning/alert if something bad happens on the server. Nagios can run on Linux operating systems. At this time, I'm using Ubuntu 16.04 for the installation.

Prerequisites

  • 2 Ubuntu 16.04 - 64bit servers
    • 1 - Nagios Host with IP: 192.168.1.9
    • 2 - Ubuntu Client with IP: 192.168.1.10
  • Root/Sudo access

What we will do in this tutorial:

  1. Software the package dependencies like - LAMP etc.
  2. User and group configuration.
  3. Installing Nagios.
  4. Configuring Apache.
  5. Testing the Nagios Server.
  6. Adding a Host to Monitor.

Installing the prerequisites


Nagios requires the gcc compiler and build-essentials for the compilation, LAMP (Apache, PHP, MySQL) for the Nagios web interface and Sendmail to send alerts from the server. To install all those packages, run this command (it's just 1 line):


sudo apt-get install wget build-essential apache2 php
apache2-mod-php7.0 php-gd libgd-dev sendmail unzip

User and group configuration

For Nagios to run, you have to create a new user for Nagios. We will name the user "nagios" and additionally create a group named "nagcmd". We add the new user to the group as shown below:

useradd nagiosgroupadd nagcmdusermod -a -G nagcmd nagiosusermod -a -G nagios,nagcmd www-data
Adding the Nagios user

Installing Nagios

Step 1 - Download and extract the Nagios core

cd ~wget https://assets.nagios.com/downloads/nagioscore/releases/nagios-4.2.0.tar.gztar -xzf nagios*.tar.gzcd nagios-4.2.0

Step 2 - Compile Nagios

Before you build Nagios, you will have to configure it with the user and the group you have created earlier.
./configure --with-nagios-group=nagios --with-command-group=nagcmd
For more information please use: ./configure --help .
Now to install Nagios:
make allsudo make installsudo make install-commandmodesudo make install-initsudo make install-config/usr/bin/install -c -m 644 sample-config/httpd.conf /etc/apache2/sites-available/nagios.confAnd copy evenhandler directory to the nagios directory:
cp -R contrib/eventhandlers/ /usr/local/nagios/libexec/chown -R nagios:nagios /usr/local/nagios/libexec/eventhandlers

Step 3 - Install the Nagios Plugins

Download and extract the Nagios plugins:
cd ~wget https://nagios-plugins.org/download/nagios-plugins-2.1.2.tar.gztar -xzf nagios-plugins*.tar.gzcd nagios-plugin-2.1.2/

Install the Nagios plugin's with the commands below:

./configure --with-nagios-user=nagios --with-nagios-group=nagios --with-opensslmakemake install

Step 4 - Configure Nagios

After the installation phase is complete, you can find the default configuration of Nagios in /usr/local/nagios/.
We will configure Nagios and Nagios contact.
Edit default nagios configuration with vim:
vim /usr/local/nagios/etc/nagios.cfg

uncomment line 51 for the host monitor configuration.
cfg_dir=/usr/local/nagios/etc/servers

Save and exit.
Add a new folder named servers:
mkdir -p /usr/local/nagios/etc/servers

The Nagios contact can be configured in the contact.cfg file. To open it use:
vim /usr/local/nagios/etc/objects/contacts.cfg
Then replace the default email with your own email.
Set email address.

Configuring Apache

Step 1 - enable Apache modules

sudo a2enmod rewritesudo a2enmod cgi
You can use the htpasswd command to configure a user nagiosadmin for the nagios web interface
sudo htpasswd -c /usr/local/nagios/etc/htpasswd.users nagiosadmin
and type your password.

Step 2 - enable the Nagios virtualhost

sudo ln -s /etc/apache2/sites-available/nagios.conf /etc/apache2/sites-enabled/

Step 3 - Start Apache and Nagios

service apache2 restartservice nagios start

When Nagios starts, you may see the following error :

Starting nagios (via systemctl): nagios.serviceFailed

And this is how to fix it:

cd /etc/init.d/cp /etc/init.d/skeleton /etc/init.d/nagios

Now edit the Nagios file:

vim /etc/init.d/nagios

... and add the following code:

DESC="Nagios"NAME=nagiosDAEMON=/usr/local/nagios/bin/$NAMEDAEMON_ARGS="-d /usr/local/nagios/etc/nagios.cfg"PIDFILE=/usr/local/nagios/var/$NAME.lock

Make it executable and start Nagios:

chmod +x /etc/init.d/nagiosservice apache2 restartservuce nagios start

Testing the Nagios Server

Please open your browser and access the Nagios server ip, in my case: http://192.168.1.9/nagios.
Nagios Login with apache htpasswd.
Nagios Login
Nagios Admin Dashboard
Nagios Dashboard

Adding a Host to Monitor

In this tutorial, I will add an Ubuntu host to monitor to the Nagios server we have made above.
Nagios Server IP : 192.168.1.9
Ubuntu Host IP : 192.168.1.10

Step 1 - Connect to ubuntu host

ssh root@192.168.1.10

Step 2 - Install NRPE Service

sudo apt-get install nagios-nrpe-server nagios-plugins

Step 3 - Configure NRPE

After the installation is complete, edit the nrpe file /etc/nagios/nrpe.cfg:
vim /etc/nagios/nrpe.cfg
... and add Nagios Server IP 192.168.1.9 to the server_address.
server_address=192.168.1.9
Configure server address

Step 4 - Restart NRPE

service nagios-nrpe-server restart

Step 5 - Add Ubuntu Host to Nagios Server

Please connect to the Nagios server:
ssh root@192.168.1.9
Then create a new file for the host configuration in /usr/local/nagios/etc/servers/.
vim /usr/local/nagios/etc/servers/ubuntu_host.cfg
Add the following lines:
# Ubuntu 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
}
define service {
      host_name                       ubuntu_host
      service_description             Check Users
      check_command           check_local_users!20!50
      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
}
define service {
      host_name                       ubuntu_host
      service_description             Local Disk
      check_command                   check_local_disk!20%!10%!/
      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
}
define service {
      host_name                       ubuntu_host
      service_description             Check SSH
      check_command                   check_ssh
      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
}
define service {
      host_name                       ubuntu_host
      service_description             Total Process
      check_command                   check_local_procs!250!400!RSZDT
      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

}
You can find many check_command in /usr/local/nagios/etc/objects/commands.cfg file. See there if you want to add more services like DHCP, POP etc.
And now check the configuration:
/usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg
... to see if the configuration is correct.

Step 6 - Restart all services

On the Ubuntu Host start NRPE Service:
service nagios-nrpe-server restart
... and on the Nagios server, start Apache and Nagios:
service apache2 restartservice nagios restart

Step 7 - Testing the Ubuntu Host

Open the Nagios server from the browser and see the ubuntu_host being monitored.
The Ubuntu host is available on monitored host.

Monitored server is listed
All services monitored without error.
All services are green





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