Comment # 37 on bug 1122614 from Guillaume GARDET

(In reply to Michael Chang from comment #36)
> Hi Guillaume,
> 
> Could you please check if you seen the message "Please press 't' to show the
> boot menu on this console" and pressing the "t" could bring the menu or not ?

No, the last message on serial is: 
  Welcome to GRUB!

Whereas with previous grub2.02, I also have the following lines after the
welcome message:
  Waiting for Ethernet connection... done.
  Please press 't' to show the boot menu on this console

> If not working, could you please try modifying /etc/default/grub with:
> 
>  GRUB_TERMINAL="console"
> 
> And run "grub2-mkconfig -o /boot/grub2/grub.cfg" to direct using the
> firmware console at boot, thus will eliminate the hotkey 't' not being
> functional. And if still not work, problem might be within the console
> terminal itself.

GRUB_TERMINAL="console" option allows to have the menu on serial console.