I am running Ubuntu 17.04. This happens inside X, after I have logged in. I'm running the default install of Ubuntu Gnome https://ubuntugnome.org/
I have the following code inside
[[ -z "$TMUX" ]] && exec tmux # Launch tmux in new shells
When I reboot and login with this in my bashrc then ALT+LEFT and ALT+RIGHT switch to the previous and next tty, respectively.
When I remove the line, then ALT+LEFT and ALT+RIGHT go back to their usual behaviour of going back and forward in my browser.
Am I launching tmux wrong?