Don't know if this is useful, but it took me a while to figure it out. Thanks to user k1l from IRC channel. In order to force your machine (ubuntu, powerpc, yaboot) to boot to shell mode and not gui:

1. Enter in terminal:

Code:
sudo systemctl set-default multi-user.target
2. Reboot

Voila !

If you need to reverse this:

1. Enter in terminal:

Code:
sudo systemctl set-default graphical.target
2. Reboot.

Thanks k1l !!