In the OpenNMS container image is the hostname command missing. It was available until Horizon 29.0.5 but with Horizon 29.0.6+ it doesn't exist. We have a dependency on the hostname command-line tool in our Kubernetes proof of concept.
The base image for container images up to Horizon 29.0.5 used the CentOS 8 base image. With Horizon 29.0.6+ we have changed it to the CentOS 8 Stream base image which requires installing the command-line tool manually.