I have ZCS 6.0.6 (64 bit) installed on ubuntu 8.04 that I would like to upgrade to ZCS 8 on ubuntu 12.04. Are there instructions for this?

I tried to do it by making a copy of the old 6.0.6 /opt/zimbra tree on a newly installed ubuntu 12.04 VM and running the ZCS 8 install.sh. But that doesn't create everything needed (/opt/zimbra/conf/saslauthd.conf isn't created, for example)