Ubuntu 20.04.3 LTS, qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "" even though it was found.

qtcsp

Hello all,
This is my first post in the forum, so kindly excuse me for being naive. I am trying on open Paraview (a visualizing software) from my home terminal (Ubuntu 20.04.3 LTS), but unable to get it working, since it is giving me an error which says:

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: xcb.

error: exception occurred: Subprocess aborted

Surprisingly the Paraview was working nicely some days ago and suddenly it stopped with the above-mentioned error. I guess something related to the update/upgrade had not worked correctly. Also, I installed a new software called "wine" and thought it might be the culprit thus removed that also, but that also didn't worked. I tried all the possible ways to resolve it mentioned in this forum like:

sudo apt-get install libx11-xcb1

Also tried to run Paraview after running this flag

export QT_DEBUG_PLUGINS=1

and got the following output:

QFactoryLoader::QFactoryLoader() checking directory path "/home/csp/OpenFOAM/csp-v2106/ParaView-5.10.0-RC1-MPI-Linux-Python3.9-x86_64/plugins/platforms" ...
QFactoryLoader::QFactoryLoader() looking at "/home/csp/OpenFOAM/csp-v2106/ParaView-5.10.0-RC1-MPI-Linux-Python3.9-x86_64/plugins/platforms/libqxcb.so"
Found metadata in lib /home/csp/OpenFOAM/csp-v2106/ParaView-5.10.0-RC1-MPI-Linux-Python3.9-x86_64/plugins/platforms/libqxcb.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "xcb"
        ]
    },
    "archreq": 0,
    "className": "QXcbIntegrationPlugin",
    "debug": false,
    "version": 330752
}


Got keys from plugin meta data ("xcb")
QFactoryLoader::QFactoryLoader() checking directory path "/home/csp/OpenFOAM/csp-v2106/ParaView-5.10.0-RC1-MPI-Linux-Python3.9-x86_64/bin/platforms" ...
Cannot load library /home/csp/OpenFOAM/csp-v2106/ParaView-5.10.0-RC1-MPI-Linux-Python3.9-x86_64/plugins/platforms/libqxcb.so: (/lib/x86_64-linux-gnu/libQt5XcbQpa.so.5: undefined symbol: _ZTI20QEventDispatcherGlib, version Qt_5_PRIVATE_API)
QLibraryPrivate::loadPlugin failed on "/home/csp/OpenFOAM/csp-v2106/ParaView-5.10.0-RC1-MPI-Linux-Python3.9-x86_64/plugins/platforms/libqxcb.so" : "Cannot load library /home/csp/OpenFOAM/csp-v2106/ParaView-5.10.0-RC1-MPI-Linux-Python3.9-x86_64/plugins/platforms/libqxcb.so: (/lib/x86_64-linux-gnu/libQt5XcbQpa.so.5: undefined symbol: _ZTI20QEventDispatcherGlib, version Qt_5_PRIVATE_API)"
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: xcb.

error: exception occurred: Subprocess aborted

As of now, I am really stuck and not been able to figure out what's wrong is happening, my output for

qmake --version

are:

QMake version 3.1
Using Qt version 5.9.7 in /home/csp/anaconda3/lib

Could anyone please help? Any further suggestion will save a lot of time, since I have been struggling with this problem for a quite long time, thanks in advance.

mrjj

Hi
If it did work then something must been changed.

have a look with
ldd /usr/lib/qt/plugins/platforms/libqxcb.so
(adjust path if you did install some place else)

Look for something like
libxcb-util.so.1 => not found

The normal fix for a clean 20.04 and the "Could not load the Qt platform plugin "xcb"
is
sudo apt-get install libxcb-randr0-dev libxcb-xtest0-dev libxcb-xinerama0-dev libxcb-shape0-dev libxcb-xkb-dev

but since it did work at first, I think something else is up.

qtcsp

Thanks a lot @mrjj but could you suggest what else could be done to figure this out?

mrjj

@qtcsp

Well the normal is to look for missing .SO files

The LDD on libqxcb did not show anything missing ?

It does this say fail to load
LoadPlugin failed on "/home/csp/OpenFOAM/csp-v2106/ParaView-5.10.0-RC1-MPI-Linux-Python3.9-x86_64/plugins/platforms/libqxcb.so

so try run ldd on that version and see.

JonB

@qtcsp
In addition to @mrjj telling you to run

ldd /home/csp/OpenFOAM/csp-v2106/ParaView-5.10.0-RC1-MPI-Linux-Python3.9-x86_64/plugins/platforms/libqxcb.so

your actual error message tells you:

(/lib/x86_64-linux-gnu/libQt5XcbQpa.so.5: undefined symbol: _ZTI20QEventDispatcherGlib, version Qt_5_PRIVATE_API)

Also run

ldd /lib/x86_64-linux-gnu/libQt5XcbQpa.so.5

It looks like you have a mixture of Qt libraries, some in /lib/... and some in /home/csp/OpenFOAM/csp-v2106/ParaView-5.10.0-RC1-MPI-Linux-Python3.9-x86_64/.... My thought is there might be some incompatibility with them looking for different versions of Qt.

qtcsp

@JonB Thanks a lot for your help. So, should I run all of them one by one to make it work? If possible could be please simplify these steps in a more friendly way (kindly assume me as a begineer)?
I am really confused if this is the issue of QT/Ubuntu or Paraview. Thus, really unsure of the correct platform. Sincerely thankful to you for your kind help.

JonB

@qtcsp
ldd won't "make it work". It will tell you if the .so files are missing further dependencies, which is what we need to know. Look at the output it produces, particularly for any "not found"s.

If possible could be please simplify these steps in a more friendly way

In what way "simplify" or "friendly"? I have given you the commands you need to type....

qtcsp

@JonB Thanks again for your help. By typing

ldd /lib/x86_64-linux-gnu/libQt5XcbQpa.so.5

I am getting the following output:

        linux-vdso.so.1 (0x00007ffd46df1000)
	libQt5XcbQpa.so.5 => /lib/x86_64-linux-gnu/libQt5XcbQpa.so.5 (0x00007fb1a763c000)
	libfontconfig.so.1 => /lib/x86_64-linux-gnu/libfontconfig.so.1 (0x00007fb1a75f5000)
	libfreetype.so.6 => /lib/x86_64-linux-gnu/libfreetype.so.6 (0x00007fb1a7536000)
	libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007fb1a7518000)
	libQt5Gui.so.5 => /lib/x86_64-linux-gnu/libQt5Gui.so.5 (0x00007fb1a6f2d000)
	libQt5Core.so.5 => /lib/x86_64-linux-gnu/libQt5Core.so.5 (0x00007fb1a69e4000)
	libGL.so.1 => /lib/x86_64-linux-gnu/libGL.so.1 (0x00007fb1a695c000)
	libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007fb1a6939000)
	libX11-xcb.so.1 => /lib/x86_64-linux-gnu/libX11-xcb.so.1 (0x00007fb1a6934000)
	libxcb.so.1 => /lib/x86_64-linux-gnu/libxcb.so.1 (0x00007fb1a6908000)
	libXrender.so.1 => /lib/x86_64-linux-gnu/libXrender.so.1 (0x00007fb1a66fe000)
	libXext.so.6 => /lib/x86_64-linux-gnu/libXext.so.6 (0x00007fb1a66e9000)
	libX11.so.6 => /lib/x86_64-linux-gnu/libX11.so.6 (0x00007fb1a65ac000)
	libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007fb1a645d000)
	libSM.so.6 => /lib/x86_64-linux-gnu/libSM.so.6 (0x00007fb1a6452000)
	libICE.so.6 => /lib/x86_64-linux-gnu/libICE.so.6 (0x00007fb1a6432000)
	libxkbcommon-x11.so.0 => /lib/x86_64-linux-gnu/libxkbcommon-x11.so.0 (0x00007fb1a6427000)
	libxkbcommon.so.0 => /lib/x86_64-linux-gnu/libxkbcommon.so.0 (0x00007fb1a63e5000)
	libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007fb1a63df000)
	libstdc++.so.6 => /lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007fb1a61fd000)
	libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007fb1a61e2000)
	libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007fb1a5fee000)
	libQt5DBus.so.5 => /lib/x86_64-linux-gnu/libQt5DBus.so.5 (0x00007fb1a5f52000)
	libxcb-xinput.so.0 => /lib/x86_64-linux-gnu/libxcb-xinput.so.0 (0x00007fb1a5f2e000)
	libxcb-icccm.so.4 => /lib/x86_64-linux-gnu/libxcb-icccm.so.4 (0x00007fb1a5f27000)
	libxcb-image.so.0 => /lib/x86_64-linux-gnu/libxcb-image.so.0 (0x00007fb1a5d22000)
	libxcb-shm.so.0 => /lib/x86_64-linux-gnu/libxcb-shm.so.0 (0x00007fb1a5d1d000)
	libxcb-keysyms.so.1 => /lib/x86_64-linux-gnu/libxcb-keysyms.so.1 (0x00007fb1a5d16000)
	libxcb-randr.so.0 => /lib/x86_64-linux-gnu/libxcb-randr.so.0 (0x00007fb1a5d03000)
	libxcb-render-util.so.0 => /lib/x86_64-linux-gnu/libxcb-render-util.so.0 (0x00007fb1a5cfc000)
	libxcb-render.so.0 => /lib/x86_64-linux-gnu/libxcb-render.so.0 (0x00007fb1a5ced000)
	libxcb-shape.so.0 => /lib/x86_64-linux-gnu/libxcb-shape.so.0 (0x00007fb1a5ce8000)
	libxcb-sync.so.1 => /lib/x86_64-linux-gnu/libxcb-sync.so.1 (0x00007fb1a5cde000)
	libxcb-xfixes.so.0 => /lib/x86_64-linux-gnu/libxcb-xfixes.so.0 (0x00007fb1a5cd2000)
	libxcb-xinerama.so.0 => /lib/x86_64-linux-gnu/libxcb-xinerama.so.0 (0x00007fb1a5ccd000)
	libxcb-xkb.so.1 => /lib/x86_64-linux-gnu/libxcb-xkb.so.1 (0x00007fb1a5caf000)
	libglib-2.0.so.0 => /lib/x86_64-linux-gnu/libglib-2.0.so.0 (0x00007fb1a5b86000)
	libexpat.so.1 => /lib/x86_64-linux-gnu/libexpat.so.1 (0x00007fb1a5b58000)
	libuuid.so.1 => /lib/x86_64-linux-gnu/libuuid.so.1 (0x00007fb1a5b4d000)
	libpng16.so.16 => /lib/x86_64-linux-gnu/libpng16.so.16 (0x00007fb1a5b15000)
	libharfbuzz.so.0 => /lib/x86_64-linux-gnu/libharfbuzz.so.0 (0x00007fb1a5a10000)
	libicui18n.so.66 => /lib/x86_64-linux-gnu/libicui18n.so.66 (0x00007fb1a5711000)
	libicuuc.so.66 => /lib/x86_64-linux-gnu/libicuuc.so.66 (0x00007fb1a552b000)
	libpcre2-16.so.0 => /lib/x86_64-linux-gnu/libpcre2-16.so.0 (0x00007fb1a54a6000)
	libdouble-conversion.so.3 => /lib/x86_64-linux-gnu/libdouble-conversion.so.3 (0x00007fb1a5490000)
	/lib64/ld-linux-x86-64.so.2 (0x00007fb1a79d6000)
	libGLdispatch.so.0 => /lib/x86_64-linux-gnu/libGLdispatch.so.0 (0x00007fb1a53d8000)
	libGLX.so.0 => /lib/x86_64-linux-gnu/libGLX.so.0 (0x00007fb1a53a4000)
	libXau.so.6 => /lib/x86_64-linux-gnu/libXau.so.6 (0x00007fb1a539e000)
	libXdmcp.so.6 => /lib/x86_64-linux-gnu/libXdmcp.so.6 (0x00007fb1a5396000)
	libbsd.so.0 => /lib/x86_64-linux-gnu/libbsd.so.0 (0x00007fb1a537a000)
	libdbus-1.so.3 => /lib/x86_64-linux-gnu/libdbus-1.so.3 (0x00007fb1a5329000)
	libxcb-util.so.1 => /lib/x86_64-linux-gnu/libxcb-util.so.1 (0x00007fb1a5123000)
	libpcre.so.3 => /lib/x86_64-linux-gnu/libpcre.so.3 (0x00007fb1a50b0000)
	libgraphite2.so.3 => /lib/x86_64-linux-gnu/libgraphite2.so.3 (0x00007fb1a5083000)
	libicudata.so.66 => /lib/x86_64-linux-gnu/libicudata.so.66 (0x00007fb1a35c0000)
	libsystemd.so.0 => /lib/x86_64-linux-gnu/libsystemd.so.0 (0x00007fb1a3511000)
	librt.so.1 => /lib/x86_64-linux-gnu/librt.so.1 (0x00007fb1a3506000)
	liblzma.so.5 => /lib/x86_64-linux-gnu/liblzma.so.5 (0x00007fb1a34dd000)
	liblz4.so.1 => /lib/x86_64-linux-gnu/liblz4.so.1 (0x00007fb1a34bc000)
	libgcrypt.so.20 => /lib/x86_64-linux-gnu/libgcrypt.so.20 (0x00007fb1a339c000)
	libgpg-error.so.0 => /lib/x86_64-linux-gnu/libgpg-error.so.0 (0x00007fb1a3379000)

And by running this:

ldd /home/csp/OpenFOAM/csp-v2106/ParaView-5.10.0-RC1-MPI-Linux-Python3.9-x86_64/plugins/platforms/libqxcb.so

I am getting:

        linux-vdso.so.1 (0x00007ffddf5e8000)
	libQt5XcbQpa.so.5 => /lib/x86_64-linux-gnu/libQt5XcbQpa.so.5 (0x00007f0960d20000)
	libfontconfig.so.1 => /lib/x86_64-linux-gnu/libfontconfig.so.1 (0x00007f0960cd9000)
	libfreetype.so.6 => /lib/x86_64-linux-gnu/libfreetype.so.6 (0x00007f0960c1a000)
	libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007f0960bfc000)
	libQt5Gui.so.5 => /lib/x86_64-linux-gnu/libQt5Gui.so.5 (0x00007f0960611000)
	libQt5Core.so.5 => /lib/x86_64-linux-gnu/libQt5Core.so.5 (0x00007f09600c8000)
	libGL.so.1 => /lib/x86_64-linux-gnu/libGL.so.1 (0x00007f0960040000)
	libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f096001d000)
	libX11-xcb.so.1 => /lib/x86_64-linux-gnu/libX11-xcb.so.1 (0x00007f0960018000)
	libxcb.so.1 => /lib/x86_64-linux-gnu/libxcb.so.1 (0x00007f095ffec000)
	libXrender.so.1 => /lib/x86_64-linux-gnu/libXrender.so.1 (0x00007f095fde2000)
	libXext.so.6 => /lib/x86_64-linux-gnu/libXext.so.6 (0x00007f095fdcd000)
	libX11.so.6 => /lib/x86_64-linux-gnu/libX11.so.6 (0x00007f095fc90000)
	libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f095fb41000)
	libSM.so.6 => /lib/x86_64-linux-gnu/libSM.so.6 (0x00007f095fb36000)
	libICE.so.6 => /lib/x86_64-linux-gnu/libICE.so.6 (0x00007f095fb16000)
	libxkbcommon-x11.so.0 => /lib/x86_64-linux-gnu/libxkbcommon-x11.so.0 (0x00007f095fb0b000)
	libxkbcommon.so.0 => /lib/x86_64-linux-gnu/libxkbcommon.so.0 (0x00007f095fac9000)
	libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f095fac3000)
	libstdc++.so.6 => /lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007f095f8e1000)
	libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007f095f8c6000)
	libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f095f6d2000)
	libQt5DBus.so.5 => /lib/x86_64-linux-gnu/libQt5DBus.so.5 (0x00007f095f636000)
	libxcb-xinput.so.0 => /lib/x86_64-linux-gnu/libxcb-xinput.so.0 (0x00007f095f612000)
	libxcb-icccm.so.4 => /lib/x86_64-linux-gnu/libxcb-icccm.so.4 (0x00007f095f60b000)
	libxcb-image.so.0 => /lib/x86_64-linux-gnu/libxcb-image.so.0 (0x00007f095f406000)
	libxcb-shm.so.0 => /lib/x86_64-linux-gnu/libxcb-shm.so.0 (0x00007f095f401000)
	libxcb-keysyms.so.1 => /lib/x86_64-linux-gnu/libxcb-keysyms.so.1 (0x00007f095f3fa000)
	libxcb-randr.so.0 => /lib/x86_64-linux-gnu/libxcb-randr.so.0 (0x00007f095f3e7000)
	libxcb-render-util.so.0 => /lib/x86_64-linux-gnu/libxcb-render-util.so.0 (0x00007f095f3e0000)
	libxcb-render.so.0 => /lib/x86_64-linux-gnu/libxcb-render.so.0 (0x00007f095f3d1000)
	libxcb-shape.so.0 => /lib/x86_64-linux-gnu/libxcb-shape.so.0 (0x00007f095f3cc000)
	libxcb-sync.so.1 => /lib/x86_64-linux-gnu/libxcb-sync.so.1 (0x00007f095f3c2000)
	libxcb-xfixes.so.0 => /lib/x86_64-linux-gnu/libxcb-xfixes.so.0 (0x00007f095f3b6000)
	libxcb-xinerama.so.0 => /lib/x86_64-linux-gnu/libxcb-xinerama.so.0 (0x00007f095f3b1000)
	libxcb-xkb.so.1 => /lib/x86_64-linux-gnu/libxcb-xkb.so.1 (0x00007f095f393000)
	libglib-2.0.so.0 => /lib/x86_64-linux-gnu/libglib-2.0.so.0 (0x00007f095f26a000)
	libexpat.so.1 => /lib/x86_64-linux-gnu/libexpat.so.1 (0x00007f095f23c000)
	libuuid.so.1 => /lib/x86_64-linux-gnu/libuuid.so.1 (0x00007f095f231000)
	libpng16.so.16 => /lib/x86_64-linux-gnu/libpng16.so.16 (0x00007f095f1f9000)
	libharfbuzz.so.0 => /lib/x86_64-linux-gnu/libharfbuzz.so.0 (0x00007f095f0f4000)
	libicui18n.so.66 => /lib/x86_64-linux-gnu/libicui18n.so.66 (0x00007f095edf5000)
	libicuuc.so.66 => /lib/x86_64-linux-gnu/libicuuc.so.66 (0x00007f095ec0f000)
	libpcre2-16.so.0 => /lib/x86_64-linux-gnu/libpcre2-16.so.0 (0x00007f095eb8a000)
	libdouble-conversion.so.3 => /lib/x86_64-linux-gnu/libdouble-conversion.so.3 (0x00007f095eb74000)
	/lib64/ld-linux-x86-64.so.2 (0x00007f09610ba000)
	libGLdispatch.so.0 => /lib/x86_64-linux-gnu/libGLdispatch.so.0 (0x00007f095eabc000)
	libGLX.so.0 => /lib/x86_64-linux-gnu/libGLX.so.0 (0x00007f095ea88000)
	libXau.so.6 => /lib/x86_64-linux-gnu/libXau.so.6 (0x00007f095ea82000)
	libXdmcp.so.6 => /lib/x86_64-linux-gnu/libXdmcp.so.6 (0x00007f095ea7a000)
	libbsd.so.0 => /lib/x86_64-linux-gnu/libbsd.so.0 (0x00007f095ea5e000)
	libdbus-1.so.3 => /lib/x86_64-linux-gnu/libdbus-1.so.3 (0x00007f095ea0d000)
	libxcb-util.so.1 => /lib/x86_64-linux-gnu/libxcb-util.so.1 (0x00007f095e807000)
	libpcre.so.3 => /lib/x86_64-linux-gnu/libpcre.so.3 (0x00007f095e794000)
	libgraphite2.so.3 => /lib/x86_64-linux-gnu/libgraphite2.so.3 (0x00007f095e767000)
	libicudata.so.66 => /lib/x86_64-linux-gnu/libicudata.so.66 (0x00007f095cca4000)
	libsystemd.so.0 => /lib/x86_64-linux-gnu/libsystemd.so.0 (0x00007f095cbf5000)
	librt.so.1 => /lib/x86_64-linux-gnu/librt.so.1 (0x00007f095cbea000)
	liblzma.so.5 => /lib/x86_64-linux-gnu/liblzma.so.5 (0x00007f095cbc1000)
	liblz4.so.1 => /lib/x86_64-linux-gnu/liblz4.so.1 (0x00007f095cba0000)
	libgcrypt.so.20 => /lib/x86_64-linux-gnu/libgcrypt.so.20 (0x00007f095ca80000)
	libgpg-error.so.0 => /lib/x86_64-linux-gnu/libgpg-error.so.0 (0x00007f095ca5d000)

JonB

@qtcsp
There is nothing wrong in this output. So that is not the issue. We are left with:

QLibraryPrivate::loadPlugin failed on "/home/csp/OpenFOAM/csp-v2106/ParaView-5.10.0-RC1-MPI-Linux-Python3.9-x86_64/plugins/platforms/libqxcb.so" : "Cannot load library /home/csp/OpenFOAM/csp-v2106/ParaView-5.10.0-RC1-MPI-Linux-Python3.9-x86_64/plugins/platforms/libqxcb.so: (/lib/x86_64-linux-gnu/libQt5XcbQpa.so.5: undefined symbol: _ZTI20QEventDispatcherGlib, version Qt_5_PRIVATE_API)"

This implies to me that ParaView's libqxcb.so is trying to access a private symbol in libQt5XcbQpa.so.5, and it can't.

I know no more than that. I am thinking the ParaView libqxcb.so is not compatible with the libQt5XcbQpa.so.5 from the system-installed Qt version. maybe go check what version of Qt your ParaView expects you to have?

qtcsp

@JonB Many thanks for the consistent help. You are correct, maybe time to open a query thread on the Paraview forum. Meanwhile, I found something related to this issue in the Paraview forum, previously also some folks have reported similar issues. Maybe I will get some help from there too. Thanks again for your help and sorry for asking the very fundamental query regarding ldd etc. You have been really very prompt and helpful, sincere thanks to you @JonB and @mrjj

SGaist

Hi,

One issue here is that your anaconda installed software is trying to use part your system installed Qt.

I would say that the packaging of ParaView is wrong. At the very least the Qt version provided with it looks incomplete.