“Failed to load session “ubuntu” problem solving summary :

1.
sudo apt-get update
sudo apt-get install
sudo apt-get install
sudo dpkg-reconfigure ubuntu-desktop
Sudo reboot
sudo apt-get install gnome-session
sudo apt-get install lightdm
sudo apt-get install unity-greeter
sudo dpkg-reconfigure lightdm

2. Rebooting the computer appears. Unable to login in the login screen. User login failed.
enter the password and return to the login interface

infinite loop, unable to find the reason.

later found that the unity-2d-launcher was not installed.

tried a lot in the middle, but nothing worked. Basically apt-get Install Unity-2D-Launcher and GnOMe-Session. I don’t know which one worked.

3
4 sudo apt-get install GDM
5

sudo apt-get install –reinstall GDM

0
1 sudo apt-get remove –purge GDM
2
3
4 sudo apt-get install GDM
5

restart invalid, as if the default is lightdm. Some people recommend GDM, I don’t care.

anyway, the problem was finally solved. Still happy.

4
3.
install apt-get unity-2d launcher gnome-session

install GDM

sudo apt-get update
0
1 sudo apt-get update
0
1 sudo apt-get GDM
2
3 default use lightdm
4
5 We’re done now.

4.

looked for some ways, finally found that GDM is not installed (GDM is GNOME graphics desktop landers), the solution:
sudo apt-get-d install –reinstall GDM

sudo apt-get remove –purge GDM

sudo apt-get install GDM