参考文章：https://blog.csdn.net/qq_20965753/article/details/61420431
sudo nano /usr/share/lightdm/lightdm.conf.d/20-lubuntu.conf
[Seat:*] user-session=Lubuntu ##原有 autologin-user=username autologin-user-timeout=0
目录下文件如下：
lcpc:/usr/share/lightdm/lightdm.conf.d$ ls 20-lubuntu.conf 50-guest-wrapper.conf 50-disable-guest.conf 50-xserver-command.conf 50-disable-log-backup.conf 60-lightdm-gtk-greeter.conf 50-greeter-wrapper.conf