Using Nagios Core
Create nagiosadmin User Account
You’ll first need to create an Apache user account to be able to log into Nagios.
The following command will create a user account called nagiosadmin and you will be prompted to provide a password for the account.
sudo htpasswd -c /usr/local/nagios/etc/htpasswd.users nagiosadmin
When adding additional users in the future, you need to remove -c from the above command otherwise it will replace the existing nagiosadmin user (and any other users you may have added).
The login URL for Nagios is:
http://serversprivateIP/nagios
or
http://serverspublicIP/nagios
For example – http://10.25.5.143/nagios or you can use the servers DNS name