ubuntu 18.04 - disable gui on boot and login page

login 改 console:

sudo systemctl set-default multi-user.target

boot 改 console:
修改 /etc/default/grub，然後 run update-grub 讓他更新到 /boot/grub,,

#GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
...
GRUB_TERMINAL=console