20.1 Installing the GNOME Desktop Environment
It is, of course, only possible to access the desktop environment if the desktop itself has been installed. If, for example, the system was initially configured as a server it is unlikely that the desktop packages were installed. The easiest way to install the packages necessary to run the GNOME desktop is via the apt command as follows:
# apt install ubuntu-gnome-desktop
To prevent the desktop from attempting to launch automatically each time the system reboots, change the default systemd target back to multi-user:
# systemctl set-default multi-user.target
If the system has a graphical display attached, the desktop can be launched using the following command:
$ startx
If, on the other hand, the system is a server with no directly connected display, the only way to run and access the desktop will be to configure VNC support on the system.