sudo apt-get upgrade && sudo apt-get update
$ sudo apt-get upgrade
$ sudo dpkg --configure -a
$ sudo apt-get remove gnome-session gnome gnome-shell
$ sudo apt-get autoremove
$ sudo apt install ubuntu-desktop
$ sudo reboot
sudo apt-get upgrade && sudo apt-get update
$ sudo apt-get upgrade
$ sudo dpkg --configure -a
$ sudo apt-get remove gnome-session gnome gnome-shell
$ sudo apt-get autoremove
$ sudo apt install ubuntu-desktop
$ sudo reboot