This is a short note on setting up a Desktop Environment.

X is the graphical server running on a Linux machine. X does not gives you the graphical user interface directly, but provides the necessary interface to do that.

Display managers provide the log in screen. There are many different display managers. The two most popular display managers on the Ubuntu Linux distribution is gdm3 and lightdm.

On the other hand, Window managers provide the look and feel of the OS. Here, a window refers to the GUI of an application such as emacs or google-chrom. A window manager manages these windows by providing methods for arranging, hiding and displaying them. The window manager I use is awesomewm.

When you start a Ubuntu machine, you will first be greeted with the display manager. This is the screen that ask for your user name and password. At this screen you can choose an existing X session configuration and start the corresponding window manager.

You can freely change between display manager, window manager on a Linux box. In fact, you probably should. I notice a marked improve in productivity after switching to awesomewm from the default gnome window manager. In addition you can choose applications to initialize at the beginning of the X session or perform some setup.

The simplest way to change to a new window manager and starting some programs during initialization is to create a .xsession scripts. My current .xsession file look like this:

#!/usr/bin/env bash

setxkbmap -option ctrl:nocaps  # Map Caps Lock to control key

ibus-daemon &
nm-applet &
dropbox start &

gnome-settings-daemon &
gnome-keyring-daemon &

exec awesome

This file is quite straightforward. First I map the Caps Lock key to another Control key. The next 5 lines start useful programs as daemons. Finally the window manager is started.

Next we need to be able to select this new configuration somehow. This is done by creating a .desktop entry. Modern display managers can choose between different desktop environment. Notice that the little button when you sign in that allows you to choose between gnome, kde or a custom desktop environment of your choosing. To create a new entry that starts the desktop environment we defined in the .xsession script, create a new file name custom.desktop in /usr/share/xsessions with the following lines. You will probably need to use root permission.

[Desktop Entry]
Comment=Hung's a custom X session 
Keywords=Window manager

Note that the file Name is the name of the Desktop entry that will be shown in the selection panel at the display manager. Exec and TryExec contains the executable to run that actually start the desktop environment. Here by calling the Xsession command, we start with the default script ~/.xsession. More details regarding the /etc/X11/Xsession script can be found here.

You are now all set. Log out (and probably restart the Linux box). You will now see a new window manager selection called custom. Select it and enjoy.

Starting a single application in a Xsession

It is possible to load only a single application in a X session. Just change the Exec field. For example, to start only google chrome, we can do:

[Desktop Entry]
Comment=Only start Google Chrome.

However, most applications are not designed for this use-case. Hence, do expect to do extra work to get everything working perfectly. There are some alternatives:

  • Start a minimal Window Manager such as awesomewm or openbox with all bar, etc tripped off.

  • Configure the application Kiosk-style (link)