I have one in my testing environment. According to https://community.intersystems.com/post/licensing-ubuntu-and-suse-20171-and-later, I should move to native Ubuntu build with 2017.2. So I downloaded Cache for UNIX (Ubuntu Server LTS for x86-64) 2017.2.1 and tried to update my existing 2015.1.4 installation. What I got was:
Upgrade from lnxsusex64 platform is not allowed.
No packages will be installed.
Meanwhile new Cache 2017.2 instance was installed without any problem.
The question is: how to upgrade an existing one?