As far as I remember, on previous Kubuntu version (18.10) when I hit Ctrl-F9 - KWin shows all open windows. But after upgrade to 19.04 it does not work anymore. In hotkeys settings Ctrl-F9 is still shortcut for this feature, but when I press it - nothing happens and I don't know neither how to launch it from command line to see errors nor where to see logs.

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    Are you sure compositing is enabled? Shift+Alt+F12 toggles compositing which is needed for certain desktop effects including Ctrl+F9. – DK Bose May 4 at 1:36

Present Windows is a desktop effect. For it, and certain other desktop effects, to work, compositing needs to be enabled. You can check the status by opening a terminal and running:

qdbus org.kde.KWin /KWin supportInformation | grep -i composit

You may see something like this as the output:

Composite: yes; Version: 0x4
compositingMode: 1
useCompositing: true
compositingInitialized: true
windowsBlockCompositing: true
Compositing is active
Compositing Type: OpenGL

You can toggle compositing on and off using Shift+Alt+F12.

Alternatively, use the GUI to ensure that compositing is turned on when the system starts:

Set compositing enabled on startup

  • Thanks for answer. Checked "supportInformation" - "useCompositing: true". In system settings corresponding checkbox is already checked. Ctrl-F9 still does not work. – Dmitriy Vinokurov May 4 at 8:37
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    After reboot it started to work. – Dmitriy Vinokurov May 19 at 10:42
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    Question was about my personal laptop, now I faced same trouble on work PC. Compositing was enabled but command from this post shows "Compositing is not active". I solved it switching to XRender instead of OpenGL. – Dmitriy Vinokurov Jun 10 at 11:56
  • Thanks for updating! Does your work PC not have a nice GPU? – DK Bose Jun 10 at 11:59
  • lspci shows "NVIDIA Corporation GF119 [GeForce GT 610] (rev a1)" – Dmitriy Vinokurov Jun 10 at 12:06

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