Opennms Error "Caused by: org.opennms.core.schema.MigrationException: an error occurred getting the version from the database"

 This error is beacause installer (/opt/opennms/bin/install -dis) can't connect to postgresql server with standard user.

In many cases to fix this error we need to create a postgresl user and database.

systemctl start postgresql

su - postgres -c "createuser -P opennms"

su - postgres -c "createdb -O opennms opennms"

su - postgres -c "psql -U postgres" 
 

After that we need to edit the following config file to modify username/password 

 vi /etc/opennms/opennms-datasources.xml    or

vi /opt/opennms/etc/opennms-datasources.xml 

In many cases we need to edit the posegresql config file

 /var/lib/pgsql/data/pg_hba.conf with:

##local   all             all                                     peer
local   all             all                                     trust
 

##host    all             all             127.0.0.1/32            ident
host    all             all             127.0.0.1/32            trust
 

You need to add port 8980 in firewall

root@localhost:~# firewall-cmd --permanent --add-port=8980/tcp
success
root@localhost:~# systemctl restart firewalld