Found this after too much Googling so listing here for future reference.
Stop X Starting at Boot on an Upstart controlled system
update-rc.d -f remove gdm doesn’t work:
That is because Ubuntu doesn’t use System V init files for startup any more, it uses a program called Upstart. You have to edit the file /etc/init/gdm.conf and comment the ‘start’ line to obtain something like:
Code: #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)) stop on runlevel