Failed to load session "ubuntu" problem solving summary

1. Use sudo lightdm to enable the default interface and find that it is not installed, then execute
sudo apt-get install lightdm to install

and then execute sudo lightdm to start the interface,
but after entering the password, it prompts:
Failed to load session "ubuntu

use the following steps to solve:

sudo apt- get update
sudo apt-get install ubuntu-desktop
sudo apt-get -f install
sudo dpkg-reconfigure ubuntu-desktop
sudo reboot