01.进入目录
cd /usr/share/lightdm/lightdm.conf.d02.查看文件
ls
50-disable-log-backup.conf 50-ubuntu.conf 50-xserver-command.conf
50-greeter-wrapper.conf 50-ubuntu.conf.bak
50-guest-wrapper.conf 50-unity-greeter.conf03.备份
sudo cp 50-ubuntu.conf 50-ubuntu.conf.bak04.编辑50-ubuntu.conf并保存
[Seat:*]
user-session=ubuntu
allow-guest=false 添加：allow-guest=false