I saw this error message,
19-03-21 15:13:52 ERROR (SyncWorker_2) [hassio.docker] Can't start addon_core_mosquitto: 500 Server Error: Internal Server Error ("driver failed programming external connectivity on endpoint addon_core_mosquitto (4b8f3bf237d79235e35965bf2de0e0ff7a3186c457c8047e0d942f1737578250): Error starting userland proxy: listen tcp 0.0.0.0:1883: bind: address already in use")
in my config i used 127.0.0.1 on my ubuntu server
I use docker for everything except mosquitto, mosquitto i installed by using sudo apt-get install mosquitto