Comment 2 for bug 1516255

I had the same undefined symbol problem as @dolzenko with the `zenity` component too after a 15.10 upgrade. This caused Mir not to start (black screen) and no access to terminal either without going into recovery mode. I had also installed version 2.6.1 of the google protobuf library from source (github).

I fixed my system by manually uninstalling the google protobuf library from /usr/local/ and then re-installing libmirprotobuf. Upon reboot 15.10 then started working normally.

Not sure why, but the installation of google protobuf causes libmirprotobuf not to be subsequently installed / upgraded correctly.