WSL2 on Windows 11 (Ubuntu 20.04): cannot run Qt apps, "could not connect to display: :0", xcb module found but not loaded

Question

Qt apps work from Terminal-hosted WSL, but not from window WSL.

I am trying to run a Qt app, such as xeyes, on WSL2 with Ubuntu 20.04, on Windows 11. When I launch it (xeyes, or Wireshark, or Qt-made software from my company), I have an error: Error: Can't open display: :0.

Depending on the software, the error can be detailed as:

user@PC:~$ wireshark
qt.qpa.xcb: could not connect to display: :0
qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "" even though it was found

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For the sake of legibility, I will start code lines like that:

• C:\Users\me> foo is the Windows terminal (CMD)
• bash-5.0$ fight is WSL called from the terminal (in the same window)
• user@PC:~$ is WSL started from Windows 11, from the desktop, in a separate window. It is supposed to be the exact same thing, but apparently not...

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The weird thing is that I can run these if I start WSL2 from CMD. But not in my main WSL installation, the one that I start from a shortcut on my Windows desktop.

There are a lot of questions on the subject: Here, here, here. None of the solutions work for my system. My takeaway is that on start-up, WSL changes a network configuration.

How to reproduce

If I open Terminal (Windows command invite) and start WSL from there, it works:

C:\Users\me> wsl ~ -e bash --norc --noprofile
bash-5.0$ xeyes               # --> xeyes work

But if I open WSL directly from Windows, it does not work.

user@PC:~$ xeyes
Error: Can't open display: :0

And the weird thing is, once I opened WSL2, I can't start the app from CMD-hosted WSL again.

C:\Users\me> wsl ~ -e bash --norc --noprofile
bash-5.0$ xeyes
Error: Can't open display: :0

My conclusion is that something in WSL2 changed network settings at launch.

Possible leads

I tried changing the DISPLAY variable.

• user@PC:~$ export DISPLAY=0.0.0.0 --> same error
• user@PC:~$ export DISPLAY=0.0.0.0:0 --> runs for several minutes, then same error
• user@PC:~$ export DISPLAY=10.0.0.3 (local IP) --> same error
• user@PC:~$ export DISPLAY=10.0.0.3:0 --> runs for several minutes, then same error
• user@PC:~$ export DISPLAY=[route] putting the default route --> same error

In all cases, the problem must not be DISPLAY, because it has the same default value in CMD and WSL2.

WSL from Windows desktop:

user@PC:~$ echo $DISPLAY --> :0

WSL from Terminal:

C:\Users\me> wsl ~ -e bash --norc --noprofile
bash-5.0$ echo $DISPLAY
bash-5.0$ :0

I thought maybe WSL from desktop changes the network settings. But both ifconfig and ip route show return exactly the same parameters. I also have nothing in my .bashrc that could modify them, at least I think so.

Answer 1

I am on Windows 10, WSL2 on Ubuntu.

Try the following export QT_QPA_PLATFORM="xcb" sudo apt install libxcb-xinerama0 libqt5x11extras5