问题

请看最后一行

Started GNOME display manager... and deal with any system changes..p link was shut down.....

答案1

Alt+F2 ，启动终端会话，能够登录。

sudo apt purge gdm gdm3


sudo apt install gdm3 ubuntu-desktop


systemctl restart gdm

答案2

这是版本3.16的bug，

sudo apt-get install lightdm


sudo dpkg-reconfigure lightdm