Finally I have been able to add a host. This failed for 2 reasons, firstly I didn't edit libvirtd.conf correctly; with mdns_adv = 1 , it should equal 0, this prevented libvirtd from starting, and thus in turn cloudstack-agent.
Secondly, I don't know if there's a typo in the documentation, but I had to use this network interface configuration; swapping eth0 and cloudbr0's static and manual lines:- # The primary network interface auto eth0 iface eth0 inet manual # Public network auto cloudbr0 iface cloudbr0 inet static address 192.168.42.11 netmask 255.255.255.240 gateway 192.168.42.1 dns-nameservers 8.8.8.8 8.8.4.4 dns-domain lab.example.org` bridge_ports eth0 bridge_fd 5 bridge_stp off bridge_maxwait 1 # Private network auto cloudbr1 iface cloudbr1 inet manual bridge_ports none bridge_fd 5 bridge_stp off bridge_maxwait 1