I have got some applications such as KColorChooser, KBreakOut, MadView3D which are not showing any application icon on the dock when they are active. Only a square with no icon is shown. Also, When I hover over them, instead of the application name, unknown is shown.
enter image description here

I am using Gnome as my desktop environment on Ubuntu 20.04. Why does this happen and how to fix this?

2 Answers 2


I have solved the problem with the help of this video: https://youtu.be/xZ_M3Q-U-J0.

Here is the summary:
Gnome (and any other Desktop) identify instances of an application and keeps track of them with the WM_CLASS property.
Some of the KDE applications do not provide a WM_CLASS property within them and due to this missing WM_CLASS property, Gnome cannot keep track of the applications and therefore cannot associate the icons with them. Every time a new instance of that same app is created, it shows a new element on the dock.
This problem also occurs in KDE plasma: https://forum.kde.org/viewtopic.php?f=289&t=160452


  • Open the application which behaves this way.
  • Open up a terminal and issue the command xprop WM_CLASS. The mouse cursor will change to a + symbol. Click on that application with the + shaped cursor. The WM_CLASS string will be printed out on the terminal.
    enter image description here
  • Copy the .desktop file of that application from /usr/share/applications/ folder to your local directory ~/.local/share/applications/ folder. For me, it was named org.kde.kcolorchooser.desktop.
    Do not modify the original file, because it will get replaced whenever the application is updated.
  • Open the file in a text editor and add the line StartupWMClass=<WM_CLASS> where <WM_CLASS> should be replaced by the string you got from the above command. For me, it was StartupWMClass=kcolorchooser.
  • Save the file and enjoy! The problem will be gone.

If you are facing issues with the Ubuntu taskbar icons, please run this commands to get rid of taskbar icon missing problem.

sudo update-icon-caches /usr/share/icons/*

sudo apt install --reinstall gnome-control-center

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