I have a very similar issue like you, although on Win10. You can lookup my topic "RPC connection issue...". I think it has to to with the RPC (Remote Procedure Calls), where armorydb tires to connect to bitcoind, but fails to do so. There have been changes with the port selection from static to dynamic and for some reason that doesn't seem to work with some OS.

Could you post your armorydb log (dbLog.txt) instead of armorylog.txt. You should find it in your home directory. In windows this is C:/Users/../AppData/Armory or %APPDATA/Armory%. In Ubuntu it should be "/home/[user]/.armory/". Because armorydb log is the seperate part of the software that handles the actual database and connection to bitcoind.

I have tired in Windows to add a new firewall rule for the Bitcoin JSON-RPC Server at TCP:8332. But I can't tell you how unix handles ports.