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Vultr profile image Sanskriti Harmukh
Sanskriti Harmukh for Vultr

Posted on with Aashish Chaurasiya Originally published at docs.vultr.com

Installing Nagios on Ubuntu 24.04

#monitoring #linux #devops #networking

Nagios Core is an open-source monitoring tool for networks, services, and applications, using the NRPE agent to collect metrics (disk, CPU, network) from remote hosts and report them on a web dashboard. This guide compiles Nagios Core from source on Ubuntu 24.04, installs plugins, and configures it to monitor a separate remote host.

Prerequisites: two Ubuntu 24.04 servers — one for Nagios, one as the monitored remote host.

Compile and Install Nagios Core

Not packaged for Ubuntu — build from source.

$ sudo apt install -y autoconf gcc libc6 make wget unzip apache2 php libapache2-mod-php libgd-dev openssl libssl-dev
$ cd
$ mkdir nagios-core
$ cd nagios-core
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Check the releases page for the current version:

$ wget -O nagioscore.tar.gz https://github.com/NagiosEnterprises/nagioscore/archive/nagios-4.5.7.tar.gz
$ tar xzf nagioscore.tar.gz
$ ls
$ cd nagioscore-nagios-4.5.7/
$ sudo ./configure --with-httpd-conf=/etc/apache2/sites-enabled
$ sudo make all
$ sudo make install-groups-users
$ sudo usermod -a -G nagios www-data
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Install Nagios and Apache Config 

$ sudo make install
$ sudo make install-daemoninit
$ sudo make install-commandmode
$ sudo make install-config
$ sudo make install-webconf
$ sudo a2enmod rewrite
$ sudo a2enmod cgi
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Create the dashboard login user:

$ sudo htpasswd -c /usr/local/nagios/etc/htpasswd.users nagiosadmin
$ sudo systemctl restart apache2
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Install Nagios Plugins 

$ sudo apt install -y autoconf gcc libc6 libmcrypt-dev make libssl-dev wget bc gawk dc build-essential snmp libnet-snmp-perl gettext
$ cd
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Check the plugins releases page for the current version:

$ wget --no-check-certificate -O nagios-plugins.tar.gz https://github.com/nagios-plugins/nagios-plugins/archive/release-2.4.12.tar.gz
$ tar zxf nagios-plugins.tar.gz
$ cd nagios-plugins-release-2.4.12
$ sudo ./tools/setup
$ sudo ./configure
$ sudo make
$ sudo make install
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Validate config and start:

$ sudo /usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg
$ sudo systemctl enable nagios
$ sudo systemctl start nagios
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Expect Total Warnings: 0 / Total Errors: 0.

Access the Dashboard 

$ sudo ufw status
$ sudo ufw allow ssh && sudo ufw enable
$ sudo ufw allow 80/tcp
$ sudo ufw reload
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Visit http://SERVER-IP/nagios, log in as nagiosadmin. Hosts in the sidebar shows localhost by default — remote hosts come next.

Set Up the Remote Host

On the remote host:

$ sudo apt install nagios-plugins nagios-nrpe-server -y
$ sudo systemctl enable --now nagios-nrpe-server
$ sudo nano /etc/nagios/nrpe.cfg
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allowed_hosts=127.0.0.1,::1,nagios_server_IP
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Replace nagios_server_IP with your Nagios server's actual IP.

$ sudo systemctl restart nagios-nrpe-server
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Configure the Nagios Server to Watch It

On the Nagios server:

$ sudo mkdir -p /usr/local/nagios/etc/servers/
$ sudo nano /usr/local/nagios/etc/servers/host.cfg
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define host {
        use                             linux-server
        host_name                       remote-app-01
        alias                           First Remote Host
        address                         remote-host-ip
        max_check_attempts              5
        check_period                    24x7
        notification_interval           30
        notification_period             24x7
}
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Replace host_name and address with your actual remote host name and IP.

$ sudo nano /usr/local/nagios/etc/nagios.cfg
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Append:

cfg_dir=/usr/local/nagios/etc/servers
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$ sudo systemctl restart nagios
$ sudo /usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg
$ sudo systemctl restart nagios
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Reload http://SERVER-IP/nagios → Hosts — the remote host now appears alongside localhost.

Next Steps

Nagios is monitoring both the local server and a remote host over NRPE. From here:

  • Install NRPE on additional hosts and add matching host.cfg entries to scale monitoring out
  • Configure notification contacts (email, etc.) so alerts actually reach someone
  • Add service checks (disk, CPU, custom scripts) beyond the default host checks

For the full guide, visit the original article on Vultr Docs.

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