Debian apt update failed on expired GPG keys, and i couldn't quite figure out how to make it ignore the errors. So I made it worse.
First I tried to install freebsd. It mentions Power7 for the ppc64 version, but it doesn't work on my IBM server. It probably only works in a VM. Next up a fresh Debian iso. And that gave more issues.
The important thing to know is that Power7 is the last processor family that isn't supported by the Debian little endian powerpc port. IBM dropped support for the platform about two years ago, and most distros that had a port stopped development.
The only holdout I knew about was an unofficial Debian port. This worked, but because it is an unstable version things unexpectedly break. And this time the installer couldn't find the repository with all the software packages. I installed it with broken apt support, got a minimal system, and could start with attempt number two of fixing it.
The trick was to point apt to http://ftp.ports.debian.org and tell it to ignore GPG by adding [trusted=yes] in the sources list for each source.
This all took about a day. I got a better appreciation of how stable x86 versions are, because every time I poke around with unsupported architectures I learn something new about linux which I didn't quite wanted to know.
p.s.
I found an opensuse linux version while writing this, so more Power7 adventures soon(tm)