OpenTX Companion on Ubuntu
To install OpenTX Companion on Ubuntu just follow the instructions on https://launchpad.net/~opentx-test/+archive/ubuntu/rel:
$ sudo add-apt-repository ppa:opentx-test/rel
$ sudo apt-get update
$ sudo apt-get install opentx-companion22
Then to launch it from the command line:
$ companion22
After that setup is the same as on Windows and Mac. And as with those platforms OpenTX Companion only works with the transmitter when it is started in bootloader mode (normal mode and connecting while its off don't work).
Note: I have automounting of USB drives disabled. So while the drives show up in Unity I had to explicitly open the Taranis drive (and so trigger mounting) before Companion could get the EEPROM.BIN file it needs if you want to load exisitng models.