To configure OpenNMS, we will be using the Ubuntu server, which has been updated to the latest stable version. Once we are done with updating the server, we need to make a few configurations to get our system ready for installing and configuring OpenNMS:

1. To begin, we will edit the /etc/hosts file to set a proper and fully qualified domain name for our server:

Here, we have added example.OpenNMS.local as the domain name for our server.

2. Next, we edit /etc/hostname and update the same domain name:

3. OpenNMS uses PostgreSQL for its database purposes. Hence, we will install PostgreSQL using the following command:

4. Once the installation completes, we will allow user access to the database for our root account by editing the /etc/postgresql/9.5/main/pg_hba.conf file:

Once done with these changes, save and close the file.

5. Now, restart PostgreSQL and enable it so that it can start on boot. Use the following command to do this:

6. Our next step is to install Java. For this, we will first add PPA to the apt source list, as follows:

7. Then, we will update the repository by running the apt-get update command. Once done, we will begin the installation of Java using the following command:

8. Once installation completes, we can check the version of Java using following command:

Now, we have our system ready to begin with the installation and configuration of OpenNMS.