Ubuntu - iniciar en modo consola - texto - terminal

http://www.guia-ubuntu.org/index.php?title=GRUB
http://wasesores.com/forzar-mostrar-grub-al-iniciar-linux/
http://wasesores.com/cambiando-el-runlevel-o-nivel-de-ejecucion-en-ubuntu/

Editamos la configuración del GDM
sudo vi /etc/init/gdm.conf
y donde dice:
start on (filesystem and started dbus and (graphics-device-added fb0 PRIMARY_DEVICE_FOR_DISPLAY=1 or drm-device-added card0 PRIMARY_DEVICE_FOR_DISPLAY=1 or stopped udevtrigger)) start on runlevel [016]
Se pone:
start on (runlevel [3]
Si lo que queremos es desactivar completamente la ejecución del GDM, pondremos:
start on (runlevel []