GUI Installation on Ubuntu Server 20.04
Update the apt package index and install tasksel.
$ sudo apt update
$ sudo apt install tasksel
List the GUI we have installed and we can install:
$ sudo tasksel –list-tasks
Main available Graphical User Interfaces (GUI) installations using tasksel’s tasks
Task Description
kubuntu-desktop Kubuntu desktop (KDE Desktop)
lubuntu-desktop Lubuntu Desktop (LXQt desktop)
ubuntu-budgie-desktop Ubuntu Budgie desktop
ubuntu-desktop Ubuntu desktop (default GNOME)
ubuntu-desktop-minimal Ubuntu minimal desktop (default GNOME)
ubuntu-mate-desktop Ubuntu MATE desktop
ubuntustudio-desktop Ubuntu Studio desktop (Xfce-based desktop)
ubuntustudio-desktop-core Ubuntu Studio minimal DE installation (Xfce-based desktop)
xubuntu-desktop Xubuntu desktop (Xfce desktop)
Use tasksel command to install the selected GUI. For example to install the default Ubuntu GNOME desktop execute. This step will install all the files and take some time to finish.
$ sudo tasksel install ubuntu-desktop
Run the following command to make sure our system boots into the graphical target after reboot
$ sudo systemctl set-default graphical.target
Run command sudo reboot to reboot. At this point, the GUI should start.
$sudo reboot
文章来自：Install GUI on Ubuntu 20.04 Quick Guide
how to install gui on ubuntu server