====== How to run an X program without a desktop environment ======

In general it is not possible to run a GNU/Linux program which features a Graphical User Interface from a **text only console**. For example I had a **Python** progam using the **PyQt5** library, if I start it from a virtual terminal I get the following error:

<code>
qt.qpa.xcb: could not connect to display 
qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "" even though it was found.
This application failed to start because no Qt platform plugin could be initialized.
Reinstalling the application may fix this problem.

Available platform plugins are: eglfs, linuxfb, minimal, minimalegl, offscreen, vnc,
wayland-egl, wayland, wayland-xcomposite-egl, wayland-xcomposite-glx, xcb.

Aborted
</code>

In some circumstances it is not desiderable to start the **full desktop environment** (e.g. XFCE or Gnome), but you can still relay on the **X.org server** to handle the graphics. On a Debian GNU/Linux you can use the **startx** command (provided by the **xinit** package) to start the X.org server and to execute just one program:

<code bash>
startx /path/to/my-program.py --arg1 --arg2 > /dev/null 2>&1
</code>

===== Using the full screen =====

In my case I had to adjust the Python program to enable it in using **the entire screen space**.

The program initially calls the **QMainWindow.setGeometry()** with a reduced geometry which leaves some room for the window decorations (title bar, borders, etc.) and for the desktop environment elements (panels, etc.). When the program calls later the **QMainWindow.showFullScreen()** function, everything is properly resized to fill the entire screen. This approach works fine into a normal desktop environment, but when the program is run directly by ''startx'', the ''showFullScreen()'' does not fill the entire screen.

To solve the problem I have to initialize the ''QMainWindow.setGeometry()'' with the entire screen size. In pseudo Python code, something like this:

<code python>
class myApp(QMainWindow):
    def __init__(self):
        super(myApp, self).__init__()
            screen_width = app.desktop().availableGeometry().width()
            screen_height = app.desktop().availableGeometry().height()
            self.setGeometry(0, 0, screen_width, screen_height)

if __name__ == '__main__':
    app = QApplication(sys.argv)
    myMainWindow = myApp()
    sys.exit(app.exec_())
</code>