I did install Opennms in a VM Ubuntu on PROXMOX. Everything went well until I did change the interface IP address because the VM must work in a LAN without Internet access. Since then the opennms start correctly but the browser give me the error:
Jetty: HTTP ERROR: 503
Problem accessing /opennms/. Reason:
Service Unavailable
The problem seems to be related with the connection to Internet at the starting of opennms. When I start opens without Internet connection the server do to start correctly.
OpenNMS has a bugfix that may take care of it.