QT6: "qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "" even though it was found."

user_13285779 0
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I know that there is a great amount of answers regarding this topic, however none of them helped me. I'm using Ubunty 20.04 via Oracle VM Virtual Box and I faced exactly the same error as all other people. After building Qt6 source code using official Qt manual I'm trying to run different projects to test if everything works properly. Console-type projects build and run properly. There are no errors. Unfortunately, when I try to run Widget-type application it fails with well-known error.

t.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: eglfs, linuxfb, minimal, minimalegl, offscreen, vnc, xcb.

My collegue, who has Qt6 working properly on his Ubuntu, saw that I don't have libqxcb.so in the .../qtbase/plugins/platforms and shared it with me. Unfortunately, it didn't help much. Only the error message has changed a bit: it says that plugin was found, but couldn't be used. I tried different solutions from Internet, but none of them helped. One of the most popular

sudo apt install libxcb-icccm4 libxcb-image0 libxcb-keysyms1 libxcb-render-util0

had no impact.

Also, there's more verbose output with environmental variable QT_DEBUG_PLUGINS=1:

QFactoryLoader::QFactoryLoader() checking directory path "/home/curiouspan/qt6-build/qtbase/plugins/platforms" ...
QFactoryLoader::QFactoryLoader() looking at "/home/curiouspan/qt6-build/qtbase/plugins/platforms/libqeglfs.so"
Found metadata in lib /home/curiouspan/qt6-build/qtbase/plugins/platforms/libqeglfs.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "eglfs"
        ]
    },
    "archreq": 1,
    "className": "QEglFSIntegrationPlugin",
    "debug": true,
    "version": 393728
}


Got keys from plugin meta data QList("eglfs")
QFactoryLoader::QFactoryLoader() looking at "/home/curiouspan/qt6-build/qtbase/plugins/platforms/libqlinuxfb.so"
Found metadata in lib /home/curiouspan/qt6-build/qtbase/plugins/platforms/libqlinuxfb.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "linuxfb"
        ]
    },
    "archreq": 1,
    "className": "QLinuxFbIntegrationPlugin",
    "debug": true,
    "version": 393728
}


Got keys from plugin meta data QList("linuxfb")
QFactoryLoader::QFactoryLoader() looking at "/home/curiouspan/qt6-build/qtbase/plugins/platforms/libqminimal.so"
Found metadata in lib /home/curiouspan/qt6-build/qtbase/plugins/platforms/libqminimal.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "minimal"
        ]
    },
    "archreq": 1,
    "className": "QMinimalIntegrationPlugin",
    "debug": true,
    "version": 393728
}


Got keys from plugin meta data QList("minimal")
QFactoryLoader::QFactoryLoader() looking at "/home/curiouspan/qt6-build/qtbase/plugins/platforms/libqminimalegl.so"
Found metadata in lib /home/curiouspan/qt6-build/qtbase/plugins/platforms/libqminimalegl.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "minimalegl"
        ]
    },
    "archreq": 1,
    "className": "QMinimalEglIntegrationPlugin",
    "debug": true,
    "version": 393728
}


Got keys from plugin meta data QList("minimalegl")
QFactoryLoader::QFactoryLoader() looking at "/home/curiouspan/qt6-build/qtbase/plugins/platforms/libqoffscreen.so"
Found metadata in lib /home/curiouspan/qt6-build/qtbase/plugins/platforms/libqoffscreen.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "offscreen"
        ]
    },
    "archreq": 1,
    "className": "QOffscreenIntegrationPlugin",
    "debug": true,
    "version": 393728
}


Got keys from plugin meta data QList("offscreen")
QFactoryLoader::QFactoryLoader() looking at "/home/curiouspan/qt6-build/qtbase/plugins/platforms/libqvnc.so"
Found metadata in lib /home/curiouspan/qt6-build/qtbase/plugins/platforms/libqvnc.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "vnc"
        ]
    },
    "archreq": 1,
    "className": "QVncIntegrationPlugin",
    "debug": true,
    "version": 393728
}


Got keys from plugin meta data QList("vnc")
QFactoryLoader::QFactoryLoader() looking at "/home/curiouspan/qt6-build/qtbase/plugins/platforms/libqxcb.so"
Found metadata in lib /home/curiouspan/qt6-build/qtbase/plugins/platforms/libqxcb.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "xcb"
        ]
    },
    "archreq": 0,
    "className": "QXcbIntegrationPlugin",
    "debug": false,
    "version": 393728
}


Got keys from plugin meta data QList("xcb")
QFactoryLoader::QFactoryLoader() checking directory path "/home/curiouspan/QtTestProjects/build-WidgetTestApp-Own_Desktop-Debug/platforms" ...
Cannot load library /home/curiouspan/qt6-build/qtbase/plugins/platforms/libqxcb.so: (libQt6XcbQpa.so.6: cannot open shared object file: No such file or directory)
QLibraryPrivate::loadPlugin failed on "/home/curiouspan/qt6-build/qtbase/plugins/platforms/libqxcb.so" : "Cannot load library /home/curiouspan/qt6-build/qtbase/plugins/platforms/libqxcb.so: (libQt6XcbQpa.so.6: cannot open shared object file: No such file or directory)"
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: eglfs, linuxfb, minimal, minimalegl, offscreen, vnc, xcb.

It shows that libQt6XcbQpa.so.6 file is missing. After running ldd /home/curiouspan/qt6-build/qtbase/plugins/platforms/libqxcb.so to show the dependencies, I got the following output:

linux-vdso.so.1 (0x00007fffc8770000)
    libQt6XcbQpa.so.6 => not found
    libQt6Gui.so.6 => /home/curiouspan/qt6-build/qtbase/plugins/platforms/../../lib/libQt6Gui.so.6 (0x00007f0873306000)
    libQt6Core.so.6 => /home/curiouspan/qt6-build/qtbase/plugins/platforms/../../lib/libQt6Core.so.6 (0x00007f087295d000)
    libstdc++.so.6 => /lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007f087277c000)
    libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f087258a000)
    libEGL.so.1 => /lib/x86_64-linux-gnu/libEGL.so.1 (0x00007f0872573000)
    libX11.so.6 => /lib/x86_64-linux-gnu/libX11.so.6 (0x00007f0872436000)
    libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f0872430000)
    libQt6DBus.so.6 => /home/curiouspan/qt6-build/qtbase/plugins/platforms/../../lib/libQt6DBus.so.6 (0x00007f0872262000)
    libGLX.so.0 => /lib/x86_64-linux-gnu/libGLX.so.0 (0x00007f087222e000)
    libOpenGL.so.0 => /lib/x86_64-linux-gnu/libOpenGL.so.0 (0x00007f0872202000)

So this file is really missing. What can be the potential problem and how do I fix it? Thank you in advance!

qt6 ubuntu qt c++
5 Answers

Thank you everyone who tried to help to resolve my problem. The answer came from official Qt forum. Link to solution: https://forum.qt.io/topic/127696/qt-qpa-plugin-could-not-load-the-qt-platform-plugin-xcb-in-even-though-it-was-found/22

Basically, the problem was in lack of some dependencies. Because of specificity of Qt6 I had to install dependencies from Qt5 building manual. It's hard to say lack of which dependency caused the problem, but after installing all of them and reconfiguring and rebuilding source code, project builds properly.

user_132857790

I solved this problem by running this command in console

sudo apt install libxcb-xinerama0

The original link here

user_111460750

After fresh install QT Creator, I met the same issue. I solved it by install libxcb-xinerama0

sudo apt install libxcb-xinerama0

user_161393190

If you're on Centos, this solved the problem for me:

sudo yum install xcb-util*
user_27171690

I got this same message for a completely different reason. I had had to recreate a python virtual env from scratch after it wouldn't install tensorflow-gpu due to package inconsistencies. That environment had for many months been working correctly with qt, and I had all the qt lib*.so dependencies correctly installed. My rebuilt environment did now have tensorflow-gpu and no package inconsistencies according to conda, but my program was broken now at runtime with this Qt platform plugin xcb error. It turned out that while rebuilding the env i had installed opencv-python via pip, which installed some various Qt packages specific to opencv and python. But, if I installed qt via conda, before installing opencv-python via pip, then pip did not subsequently install those Qt packages for opencv-python, and the xcb plugin error was now fixed.

user_99831720
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