There is a new version of this tutorial available for Ubuntu 22.04 (Jammy Jellyfish).

How to Install Nagios Monitoring Software on Ubuntu 20.04 LTS

Nagios is 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, and we will be using the Ubuntu 20.04 server.

In this tutorial, we will show you step by step installing the Nagios 4.4.x on Ubuntu 20.04. We will install the Nagios Core 4.4.x from source, install the nrpe and nagios plugins, and then add host to monitor to the Nagios server.

Prerequisites

  • 2 Ubuntu 20.04 servers
    • Nagios server - hostname: nagios20 with an IP: 172.16.0.5
    • Ubuntu client - hostname: client01 with an IP: 172.16.0.6
  • Root privileges

What we will do:

  • Install Packages Dependencies
  • Install Nagios Core 4.4.6
  • Install Nagios Plugin and NRPE Plugin
  • Add Host to Monitor to Nagios Server
  • Testing

Step 1 - Install Packages Dependencies

First, we will update the Ubuntu repository and install some packages dependencies for the Nagios installation.

Update the Ubuntu repository using the apt command below.

sudo apt update

After that, install packages dependencies for Nagios installation.

sudo apt install -y autoconf bc gawk dc build-essential gcc libc6 make wget unzip apache2 php libapache2-mod-php libgd-dev libmcrypt-dev make libssl-dev snmp libnet-snmp-perl gettext

And you've installed packages dependencies for Nagios server.

Step 2 - Install Nagios Core 4.4.6

In this step, we will install the latest stable version Nagios Core 4.4.6. And we will install it manually from the source.

- Download Nagios Core 4.4.6

Go to your home directory and download the Nagios Core source code.

cd ~/
wget https://github.com/NagiosEnterprises/nagioscore/archive/nagios-4.4.6.tar.gz

Extract the Nagios package and go to the extracted Nagios directory.

tar -xf nagios-4.4.6.tar.gz
cd nagioscore-*/

- Compile and Install Nagios

First, compile Nagios source code and define the Apache virtual host configuration for Nagios.

sudo ./configure --with-httpd-conf=/etc/apache2/sites-enabled
sudo make all

Compile Nagios

Create the Nagios user and group, and add the 'www-data' Apache user to the 'nagios' group.

sudo make install-groups-users
sudo usermod -a -G nagios www-data

Nagios Add User and Group

Install Nagios binaries, service daemon script, and the command mode.

sudo make install
sudo make install-daemoninit
sudo make install-commandmode

After that, install the sample script configuration.

sudo make install-config

Then install the Apache configuration for Nagios and activate the mod_rewrite and mode_cgi modules.

sudo make install-webconf
sudo a2enmod rewrite cgi

Now restart the Apache service.

systemctl restart apache2

And you've installed the Nagios Core 4.4.6.

Compile Nagioscore

- Create nagiosadmin user

After installing the Nagios Core, we will add the basic authentication for accessing the Nagios dashboard. And we will be using the basic Apache authentication.

Create a new apache basic authentication for the user the "nagiosadmin".

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

Type your strong password.

Create Nagios Admin user

And you've created a new user 'nagiosadmin' for the Nagios dashboard authentication.

- Setup UFW Firewall

For the firewall configuration, you will need to add the Apache service and the Nagios server port to the UFW firewall.

Add the SSH and Apache HTTP port using the ufw command below.

for svc in Apache ssh
do
ufw allow $svc
done

Next, start the UFW firewall service and add it to the system boot.

ufw enable

Type 'y' and the UFW firewall service will be activate.

Now check all available rules using the command below.

ufw status numbered

Now you will get both the SSH and Apache services added to the UFW firewall.

Add Port to UFW Firewall

And finally, you've completed the Nagios Core installation on the Ubuntu 20.04 server.

Step 3 - Install Nagios Plugins and NRPE Plugin

After installing the Nagios Core, we will install the Nagios Plugins and NRPE Plugins.

Both Nagios and NRPE plugins are available by default on the Ubuntu repository. You can install those packages using the apt command below.

sudo apt install monitoring-plugins nagios-nrpe-plugin

Once the installation is complete, go to the nagios installation directory "/usr/local/nagios/etc" and create a new directory for for storing all server hosts configuration.

cd /usr/local/nagios/etc
mkdir -p /usr/local/nagios/etc/servers

Next, edit the Nagios configuration 'nagios.cfg' using vim editor.

vim nagios.cfg

Uncomment the 'cfg_dir' option that will be used for sotring all server hots configurations.

cfg_dir=/usr/local/nagios/etc/servers

Save and close.

Next edit the configuration file "resource.cfg" and define the path binary files of Nagios Monitoring Plugins.

vim resource.cfg

Define the Nagios Monitoring Plugins path by changing the default configuration as below.

$USER1$=/usr/lib/nagios/plugins

Save and close.

After that, add the nagios admin email contacts by editing the configuration file "objects/contacts.cfg".

vim objects/contacts.cfg

Change the email address with your own.

define contact{
        ......
        email [email protected]
}

Save and close.

Now define the nrpe check command by editing the configuration file "objects/commands.cfg".

vim objects/commands.cfg

Add the following configuration to the end of the line.

define command{
        command_name check_nrpe
        command_line $USER1$/check_nrpe -H $HOSTADDRESS$ -c $ARG1$
}

Save and close, and the Nagioscore configuration has been completed.

Next, start the Nagios service and add it to the system boot.

systemctl start nagios
systemctl enable nagios

Setup Nagios NRPE Plugins

The Nagios service is up and running, check using the following command.

systemctl status nagios

Below is the result.

Check Nagios Service

As a result, the Nagios service is up and running. Now we need to restart the Apache service to apply a new Nagios configuration.

systemctl restart apache2

And the Nagios configuration has been completed.

Open your web browser and type the server IP address following the "nagios" URL path.

http://172.16.0.5/nagios/

Log in with the user "nagiosadmin" and type your password.

Login to Nagios Server

And you will get the Nagios Dashboard as below.

Nagios Dashboard

As a result, you've installed Nagios on the Ubuntu 20.04 server. And you're able to add hosts to the Nagios server.

Step 5 - Add Linux Host to Monitor

In this step, we will add the Ubuntu server with hostname "client01" and the IP address "172.16.0.6" to the Nagios server.

- Install NRPE Server on the Client01 Server

Log in to the "client01" server using your ssh.

ssh [email protected]

Once you've logged in, update the Ubuntu repository and install Nagios Plugins and NRPE Server.

sudo apt update
sudo apt install nagios-nrpe-server monitoring-plugins

Next, go to the NRPE installation directory "/etc/nagios" and edit the configuration file "nrpe.cfg".

cd /etc/nagios/
vim nrpe.cfg

Uncomment the "server_address" line and change the value with the "client01" IP address.

server_address=172.16.0.6

One the "allowed_hosts" line, add the Nagios Server IP address "172.16.0.5".

allowed_hosts=127.0.0.1,::1,172.16.0.5

Save and close.

Next, edit the "nrpe_local.cfg" configuration.

vim nrpe_local.cfg

Change the IP address with the "client01" IP address, and paste the configuration into it.

command[check_root]=/usr/lib/nagios/plugins/check_disk -w 20% -c 10% -p /
command[check_ping]=/usr/lib/nagios/plugins/check_ping -H 172.16.0.6 -w 100.0,20% -c 500.0,60% -p 5
command[check_ssh]=/usr/lib/nagios/plugins/check_ssh -4 172.16.0.6
command[check_http]=/usr/lib/nagios/plugins/check_http -I 172.16.0.6
command[check_apt]=/usr/lib/nagios/plugins/check_apt

Save and close.

Now restart the NRPE service and add it to the system boot.

systemctl restart nagios-nrpe-server
systemctl enable nagios-nrpe-server

And the Nagios NRPE server is up and running.

Add Host to Nagios

Check the NRPE service using the following command.

systemctl status nagios-nrpe-server

The NRPE service is up and running.

Check Nagios NRPE Service

Next, back to the Nagios Server and check the "client01" NRPE server.

/usr/lib/nagios/plugins/check_nrpe -H 172.16.0.6
/usr/lib/nagios/plugins/check_nrpe -H 172.16.0.6 -c check_ping

And you will get the result as below.

Check NRPE Status

And you've installed the Nagios NRPE Server and Nagios Plugins on the "client01" host.

- Add Hosts Configuration to the Nagios Server

Back to the Nagios server terminal, go to the "/usr/local/nagios/etc" directory and create a new configuration "server/client01.cfg".

cd /usr/local/nagios/etc
vim servers/client01.cfg

Change the IP address and the hostname with your own and paste the configuration into it.

# Ubuntu Host configuration file1

define host {
        use                          linux-server
        host_name                    client01
        alias                        Ubuntu Host
        address                      172.16.0.6
        register                     1
}

define service {
      host_name                       client01
      service_description             PING
      check_command                   check_nrpe!check_ping
      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                       client01
      service_description             Check Users
      check_command                   check_nrpe!check_users
      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                       client01
      service_description             Check SSH
      check_command                   check_nrpe!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                       client01
      service_description             Check Root / Disk
      check_command                   check_nrpe!check_root
      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                       client01
      service_description             Check APT Update
      check_command                   check_nrpe!check_apt
      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                       client01
      service_description             Check HTTP
      check_command                   check_nrpe!check_http
      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
}

Save and close.

Now restart the Nagios Server.

systemctl restart nagios

Add Host to Nagios Server

Step 5 - Testing

Back to your browser and wait for some minutes.

Click on the "Hosts" menu and you will get the "client01" has been added.

Add Host to Nagios

Below are details monitoring about the "client01" server.

Nagios services Monitoring

Now you've added Host to monitor to the Nagios Server.

And the installation of Nagios 4.4.6 on Ubuntu 20.04 Server has been completed successfully.

Reference

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