Setup Nagios 4 in Ubuntu 20.04

You can install nagios 4 using apt-get under Ubutu 20.04.

1. Install nagios 4 and apache2 packages with snmp support.

sudo apt-get install nagios4 nagios-plugins-contrib nagios-snmp-plugins snmp-mibs-downloader apache2

2. Enable apache2's cgi module.

sudo a2enmod cgi

3. Restart both nagios and apache2 service.

sudo systemctl restart apache2
sudo systemctl restart nagios4

4.  Remember to comment out mibs: under /etc/snmp/snmp.conf.

5. Access the nagios 4 webpage via http://xxx.xxx.xxx.xxx/nagios4