root@manong:~# apt remove lightdm
root@manong:~# apt update
root@manong:~# apt install ubuntu-desktop
root@manong:~# apt install unity
root@manong:~# apt install lightdm # 选择gdm3
root@manong:~# service gdm3 start
root@manong:~# systemctl set-default graphical.target
root@manong:~# shutdown -r now