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
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
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
Create the dashboard login user:
$ sudo htpasswd -c /usr/local/nagios/etc/htpasswd.users nagiosadmin
$ sudo systemctl restart apache2
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
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
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
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
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
allowed_hosts=127.0.0.1,::1,nagios_server_IP
Replace nagios_server_IP with your Nagios server's actual IP.
$ sudo systemctl restart nagios-nrpe-server
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
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
}
Replace host_name and address with your actual remote host name and IP.
$ sudo nano /usr/local/nagios/etc/nagios.cfg
Append:
cfg_dir=/usr/local/nagios/etc/servers
$ sudo systemctl restart nagios
$ sudo /usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg
$ sudo systemctl restart nagios
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.cfgentries 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.
