I've created an application launcher in /usr/share/applications that launches rdesktop. The file specifies an icon name and I've added the icons to:


I then drug the launcher to the taskbar and the launcher with the correct logo is visible in the taskbar. However, when I start the task, a new icon is created in the taskbar, a square with a question mark in the center.

What icons do I need and where, so that the taskbar displays the correct icon for the application when it is launched?

The .desktop file contents:

[Desktop Entry]
Exec=rdesktop win7shared1 -g 1680x1000

Comment=Open windows desktop


3 Answers 3


What will most probably solve your problem is to do the following:

  1. Open the application
  2. When it is running, open a terminal and type:

    xprop WM_CLASS
  3. Then click on the open application window.

  4. The output will look like (example gedit):

    WM_CLASS(STRING) = "gedit", "Gedit"
  5. Use the first part (in this case would be gedit), to compose a line in your .desktop file:


    (replace <string> with the actual (first part of the) output of xprop WM_CLASS, e.g. StartupWMClass=gedit)

Now try again (you might have to log out / in), most likely the application will appear in the launcher under its own icon.


  • When an application starts up correctly from a launcher (.desktop file), but another icon appears with only a generic icon (question mark), it is most likely that the application window and the launcher do not connect for some reason, and the launcher does not recognize the application's window as "his". This is often the case when a script or a non- standard application (-command) is used. In those cases the StartupWMClass= line is often the solution.
  • Thanks Jacob. This resolved the problem. For the record, the WM_CLASS string was "rdesktop","rdesktop".
    – clayton
    Dec 9, 2014 at 15:06
  • @clayton perfect, glad it worked. Dec 9, 2014 at 15:16
  • 1
    Your step 2 can be reduced, as xprop lets you pass in the atom you want returned, running xprop WM_CLASS is enough Feb 22, 2016 at 16:13
  • @johndrinkwater Absolutely, thanks for the hint. It is more than a year ago, over 14 months is like another person wrote it :). Will edit... Feb 22, 2016 at 16:17
  • @jacob-vlijm :) just came across it while researching an awkward xprop behaviour Feb 23, 2016 at 21:09

for me xprop|grep WM_CLASS gave WM_CLASS(STRING) = "sun-awt-X11-XFramePeer", "jetbrains-pycharm-ce" (I was having this issue with pycharm for python)

It was the sun-awt-X11-XFramePeer that I needed as the string in my .desktop file (without quotes) - Thanks!

  • I added StartupWMClass=sun-awt-X11-XFramePeer to mine and nothing happened! Is the .desktop file located in the home folder? Aug 22, 2017 at 19:39

After putting icons into the right place, you should simply restart xserver (logout and login back).
Also try to update icon cache (simply paste code below into terminal):

for d in ~/.icons/*; do gtk-update-icon-cache -f $d; done
for d in /usr/share/icons/*; do sudo gtk-update-icon-cache -f $d; done

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