I have error message spamming the log. Eventually the light map baking seems to succeed though since the stop appearing. However, it takes super long (like 40min for what takes 1-2min on Windows.)
Note: that is using Enlighten, the experimental Progressive one doesn’t have the message but crashes Unity during baking a lot. Like every other time so it’s more than unstable and hence not usable.
You didn’t post the error message 
Make sure you’re not using Experimental Mono: Experimental Mono broken on Linux
The error message was: ‘Failed execution external process for ‘Clustering’ job’ as the title says. Nothing more.
Anyway, you were on the right track - thanks! The issue was the experimental Mono version 4.6.
For some reason ‘Mono Bleeding Edge’ made me think of a custom Mono installation not anything shipped with Unity so I never read that post. Now I know that bleeding edge means experimental in the Editor.
Ah crud, I forgot it was named Experimental in that drop-down. Updated my previous posts to be less confusing - thanks