====== How to Install a Desktop (GUI) on a Linux Ubuntu Server ======

Ubuntu Server 20.04 LTS (or previous version) does not include a Graphical User Interface (GUI) upon installation.  However, a desktop environment (a GUI) can be added after Ubuntu Server is installed.  Installation is done from the command line interface (CLI) either with or without the necessity of installing or employing the task select manager utility (tasksel), which necessity will depend on the Display Manager and/or the GUI that you choose.

===== Update the Repositories and Packages =====

Since we want to have access to the latest packages that are available to install, it is good practice to begin with updating the repositories and package lists by entering the following at the CLI.

<code>sudo apt-get update && sudo apt-get upgrade</code>

Press y and the enter key at the prompt - 'Do you want to continue?" 

If asked, enter your root/sudo password at the prompt.

This ensures that we have the most recent software updates.

===== Install the Tasksel Manager Utility =====

Tasksel is a utility for simultaneously installing related software packages.  

To install tasksel manager utility, enter the following at the CLI:

<code>sudo apt-get install tasksel</code>

If asked, enter your root/sudo password at the prompt.

===== Display Manager and GUI =====

The display manager chosen supports certain or various choices of the GUI / Desktop Environment that you select based on your choices of the look, feel, functionality of the display manager and GUI, as well as the resources that are consumed or preserved (with a heavier or more light weight display manager and/or GUI).

==== Selecting a Display Manager ====

The "default" display manager is **GDM3** which is relatively resource-intensive. The GDM3 display manager is used with and supports the **KDE-Plasma** Desktop GUI.  In order to conserve resources, there are lighter display managers in the genus to choose from, such as **SDDM**, **SLiM**, and **LightDM**. 

Here is how to install a specific display manager other than the **GDM3** default display manager.  It may involve the command line **apt-get** package manager to install, or by using the **tasksel** menu (addressed below).

The **SDDM** display manager can be installed from the **tasksel** menu during installation of **KDE** Desktop.

To install either **SLiM** or **LightDM** managers, use the **apt-get** Package manager as follows: 

To install **SLiM** enter the following at the CLI:

<code>sudo apt-get install slim</code>

To install **LightDM**, instead enter:

<code>sudo apt-get install lightdm</code>

===== Choose a Graphical User Interface (GUI) for your Ubuntu Server =====

GNOME is the mostly the default desktop GUI.

KDE is a different popular GUI. 

==== Install GNOME ====

First, launch the tasksel manager from the CLI:

<code>tasksel</code>

A graphical installation interface will appear and you are prompted to choose which software to install from a long list.  Use the down arrows to move the cursor down the list to Ubuntu desktop and press the space-bar to put a [*] next to "Ubuntu desktop."  Press **Tab** to select **OK** at the bottom of the interface list, and press Enter.  The software will install and the operating system will reboot, resulting in a graphical login screen that will be generated from the display manager (default or chosen).  For example, is we installed SLiM, then SLiM would generate the gnome ubuntu desktop login screen.

Enter you login credentials (password), to proceed to the graphical interface, in this case the GNOME UI environment.

==== Install KDE Plasma ====

To install KDE Plasma, use the following command:

<code>sudo apt-get install kde-plasma-desktop</code>

During installation, you may be asked to select a default display manager by using the arrow keys to make a selection and pressing the Enter key.

Next, launch **KDE Plasma** with one of the following commands, depending on the particular //display_manager// previously installed (namely, either SLiM, lightDM, SDDM):

<code>
sudo service Slim start

sudo service lightdm start

sudo service sddm start
</code>

If you are concerned about the substantial resource usage of these above Ubuntu Server GUI applications, then you may want to consider one of the lighter GUI applications, less resource-intensive GUI apps, listed below.  This can conserve server resources.

===== Some Lighter Graphical Interfaces =====

==== Mate Core Server Desktop ====

Mate is a popular and lightweigtht GUI which can be installed as following:

<code>sudo tasksel install ubuntu-mate-core</code>

Mate can be launched after installation with one of the 3 following choices of your installed //display manager//:

<code>
sudo service slim start

sudo service lightdm start

sudo service sddm start
</code>

You will be prompted to enter your login credentials / password.

To exit the GUI, open the command line or console and enter one of the following commands, depending on you installed //display manager// -- sudo service //display_manager// stop:

<code>
sudo service slim stop

sudo service lightdm stop

sudo service sddm stop

</code>

==== Install Lubuntu Core Server Desktop ====

Use **Lubuntu** if you want to minimize the impact on your system memory and processors (GPU and/or CPU).

To install **Lubuntu** enter:

<code>sudo tasksel install lubuntu-core</code>

Or you can alternatively install **Lubuntu** from the tasksel graphical menu list by invoking tasksel as follows:

<code>tasksel</code>

Use the arrow keys and space bar to select the Lubuntu GUI, than Tab down to the OK button and press Enter to proceed with installing Lubuntu.  

Launch The Lubuntu GUI with one of the applicable //display manager// that you have installed, as follows:

<code>
sudo service slim start

sudo service lightdm start

sudo service sddm start
</code>

==== Install Xubuntu Server Core Desktop ====

Xubuntu uses the Xfce desktop environment.

Install Xubuntu with:

<code>sudo tasksel install xubuntu-core</code>

Launch Xubuntu with:

<code>sudo service slim start

sudo service lightdm start

sudo service sddm start</code>

Login. 

==== Install Xfce Desktop ====

Install Xfce with:

<code>sudo apt-get install xfce4 slim</code>

Launch Xfce with:

<code>sudo service slim start</code>

Login.

Xfce GUI is only compatible with the SLiM display manager.

===== Switching Among Graphical Interfaces =====

If you have more than one GUI installed you can select which one GUI that you wish to use when you launch your display manager and are prompted to login. **PRESS the F1 key at the login screen** and you will be offered a selection from the multiple GUIs that are installed. Make your GUI choice and log-in with your credentials.