Our shell server, ubuntu.eskimo.com, has been upgraded to version 15.04 Vivid Vervet.
Unlike the first attempt when 15.04 first came out, this upgrade went almost flawlessly. The only boot problem being some features missing in the kernel built that this version requires and the non-existence of postgres user and group (it is in NIS but the start-up sequence with systemd doesn’t have NIS enabled at the time it tries to create the necessary log files).
These two things have been corrected and now the boot-up is 100% clean and mighty fast (takes about two seconds from launch to login).