I recently setup a Foreman 2.4/Katello 4.0 server to replace Spacewalk and everything works as expected with CentOS Hosts. I am wanting to add some Ubuntu Hosts in. I have added all the Ubuntu Repos and Synced them. I followed the guide at http://apt.atix.de/ and I am able to register the Ubuntu VMs and see them in the foreman server. On the Ubuntu VM I am able to see and use the Foreman Ubuntu Repos. My issue is that the Ubuntu Hosts do not register upgradeable packages to the Foreman server and I therefore can not push out updates from Foreman to the Ubuntu VMs. This looks to be because there is no Katello Agent for Ubuntu. Is there a way to get this to work or are there any plans to get this working in the future?
According to the ticket associated with the now merged PR, the APT applicability feature is part of Katello 4.3.
If you are using Katello 4.3 and still having problems with APT applicability, it is time to open a new thread describing in detail what you did, what worked, and what did not.