From https://askubuntu.com/a/158014
I just installed Ubuntu 16.04 dual boot on my MBP13" yesterday. For Ubuntu 16.04, here's how i did it:
Step 1: Launch terminal
Step 2: Edit X Keyboard Extension
sudo nano /usr/share/X11/xkb/symbols/pc
Step 3: Make the following changes. Ensure your file looks like this: