切换ubuntu-18.04启动方式
默认命令行形式启动
sudo systemctl set-default multi-user.target
reboot
临时使用一次图形界面进入
sudo systemctl start lightdm
默认图形界面启动
systemctl set-default graphical.target
reboot
sudo systemctl set-default multi-user.target
reboot
sudo systemctl start lightdm
systemctl set-default graphical.target
reboot