I managed to configure most of the things I wanted when using a Mac keyboard with Ubuntu. But there is one last thing : the left alt key.
Specifically, to to tilde (~), I have to press Right Alt + n. But I would prefer to do it with Left Alt...
I tried to edit the Xmodmap file.
keycode 64 = Alt_L Meta_L Alt_L Meta_L
But it doesn't work...
Also, I read that it is possible using the Keyboard Layout option. (What are the meta, super, and hyper keys?) But where is it ?!!! When I open System settings -> Keyboard, I never find the Options. I have Text entry and Shortcuts but that's it :/
Thanks for your help !