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

[JonB]

@buhtz
xcb is indeed for X11 screen display. Set environment variable QT_DEBUG_PLUGINS to 1 and then run your application. It will produce diagnostic output from which you/we can gather what it is looking for where and why it didn't get it.

[buhtz]

By the way. I installed Qt6 in Debian 11 from its backports repo. Even the qt plugins package is installed now.

qt.core.plugin.factoryloader: checking directory path "/home/user/.local/lib/python3.9/site-packages/PyQt6/Qt6/plugins/platforms" ...
qt.core.plugin.factoryloader: looking at "/home/user/.local/lib/python3.9/site-packages/PyQt6/Qt6/plugins/platforms/libqvkkhrdisplay.so"
qt.core.plugin.loader: Found metadata in lib /home/user/.local/lib/python3.9/site-packages/PyQt6/Qt6/plugins/platforms/libqvkkhrdisplay.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "vkkhrdisplay"
        ]
    },
    "archlevel": 1,
    "className": "QVkKhrDisplayIntegrationPlugin",
    "debug": false,
    "version": 394496
}


qt.core.plugin.factoryloader: Got keys from plugin meta data QList("vkkhrdisplay")
qt.core.plugin.factoryloader: looking at "/home/user/.local/lib/python3.9/site-packages/PyQt6/Qt6/plugins/platforms/libqminimalegl.so"
qt.core.plugin.loader: Found metadata in lib /home/user/.local/lib/python3.9/site-packages/PyQt6/Qt6/plugins/platforms/libqminimalegl.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "minimalegl"
        ]
    },
    "archlevel": 1,
    "className": "QMinimalEglIntegrationPlugin",
    "debug": false,
    "version": 394496
}


qt.core.plugin.factoryloader: Got keys from plugin meta data QList("minimalegl")
qt.core.plugin.factoryloader: looking at "/home/user/.local/lib/python3.9/site-packages/PyQt6/Qt6/plugins/platforms/libqvnc.so"
qt.core.plugin.loader: Found metadata in lib /home/user/.local/lib/python3.9/site-packages/PyQt6/Qt6/plugins/platforms/libqvnc.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "vnc"
        ]
    },
    "archlevel": 1,
    "className": "QVncIntegrationPlugin",
    "debug": false,
    "version": 394496
}


qt.core.plugin.factoryloader: Got keys from plugin meta data QList("vnc")
qt.core.plugin.factoryloader: looking at "/home/user/.local/lib/python3.9/site-packages/PyQt6/Qt6/plugins/platforms/libqwayland-generic.so"
qt.core.plugin.loader: Found metadata in lib /home/user/.local/lib/python3.9/site-packages/PyQt6/Qt6/plugins/platforms/libqwayland-generic.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "wayland"
        ]
    },
    "archlevel": 1,
    "className": "QWaylandIntegrationPlugin",
    "debug": false,
    "version": 394496
}


qt.core.plugin.factoryloader: Got keys from plugin meta data QList("wayland")
qt.core.plugin.factoryloader: looking at "/home/user/.local/lib/python3.9/site-packages/PyQt6/Qt6/plugins/platforms/libqminimal.so"
qt.core.plugin.loader: Found metadata in lib /home/user/.local/lib/python3.9/site-packages/PyQt6/Qt6/plugins/platforms/libqminimal.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "minimal"
        ]
    },
    "archlevel": 1,
    "className": "QMinimalIntegrationPlugin",
    "debug": false,
    "version": 394496
}


qt.core.plugin.factoryloader: Got keys from plugin meta data QList("minimal")
qt.core.plugin.factoryloader: looking at "/home/user/.local/lib/python3.9/site-packages/PyQt6/Qt6/plugins/platforms/libqeglfs.so"
qt.core.plugin.loader: Found metadata in lib /home/user/.local/lib/python3.9/site-packages/PyQt6/Qt6/plugins/platforms/libqeglfs.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "eglfs"
        ]
    },
    "archlevel": 1,
    "className": "QEglFSIntegrationPlugin",
    "debug": false,
    "version": 394496
}


qt.core.plugin.factoryloader: Got keys from plugin meta data QList("eglfs")
qt.core.plugin.factoryloader: looking at "/home/user/.local/lib/python3.9/site-packages/PyQt6/Qt6/plugins/platforms/libqxcb.so"
qt.core.plugin.loader: Found metadata in lib /home/user/.local/lib/python3.9/site-packages/PyQt6/Qt6/plugins/platforms/libqxcb.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "xcb"
        ]
    },
    "archlevel": 1,
    "className": "QXcbIntegrationPlugin",
    "debug": false,
    "version": 394496
}


qt.core.plugin.factoryloader: Got keys from plugin meta data QList("xcb")
qt.core.plugin.factoryloader: looking at "/home/user/.local/lib/python3.9/site-packages/PyQt6/Qt6/plugins/platforms/libqwayland-egl.so"
qt.core.plugin.loader: Found metadata in lib /home/user/.local/lib/python3.9/site-packages/PyQt6/Qt6/plugins/platforms/libqwayland-egl.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "wayland-egl"
        ]
    },
    "archlevel": 1,
    "className": "QWaylandEglPlatformIntegrationPlugin",
    "debug": false,
    "version": 394496
}


qt.core.plugin.factoryloader: Got keys from plugin meta data QList("wayland-egl")
qt.core.plugin.factoryloader: looking at "/home/user/.local/lib/python3.9/site-packages/PyQt6/Qt6/plugins/platforms/libqoffscreen.so"
qt.core.plugin.loader: Found metadata in lib /home/user/.local/lib/python3.9/site-packages/PyQt6/Qt6/plugins/platforms/libqoffscreen.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "offscreen"
        ]
    },
    "archlevel": 1,
    "className": "QOffscreenIntegrationPlugin",
    "debug": false,
    "version": 394496
}


qt.core.plugin.factoryloader: Got keys from plugin meta data QList("offscreen")
qt.core.plugin.factoryloader: looking at "/home/user/.local/lib/python3.9/site-packages/PyQt6/Qt6/plugins/platforms/libqlinuxfb.so"
qt.core.plugin.loader: Found metadata in lib /home/user/.local/lib/python3.9/site-packages/PyQt6/Qt6/plugins/platforms/libqlinuxfb.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "linuxfb"
        ]
    },
    "archlevel": 1,
    "className": "QLinuxFbIntegrationPlugin",
    "debug": false,
    "version": 394496
}


qt.core.plugin.factoryloader: Got keys from plugin meta data QList("linuxfb")
qt.core.plugin.factoryloader: checking directory path "/usr/bin/platforms" ...
qt.core.library: "/home/user/.local/lib/python3.9/site-packages/PyQt6/Qt6/plugins/platforms/libqxcb.so" cannot load: Cannot load library /home/user/.local/lib/python3.9/site-packages/PyQt6/Qt6/plugins/platforms/libqxcb.so: (libxcb-cursor.so.0: Kann die Shared-Object-Datei nicht öffnen: Datei oder Verzeichnis nicht gefunden)
qt.core.plugin.loader: QLibraryPrivate::loadPlugin failed on "/home/user/.local/lib/python3.9/site-packages/PyQt6/Qt6/plugins/platforms/libqxcb.so" : "Cannot load library /home/user/.local/lib/python3.9/site-packages/PyQt6/Qt6/plugins/platforms/libqxcb.so: (libxcb-cursor.so.0: Kann die Shared-Object-Datei nicht öffnen: Datei oder Verzeichnis nicht gefunden)"
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: vkkhrdisplay, minimalegl, vnc, wayland, minimal, eglfs, xcb, wayland-egl, offscreen, linuxfb.

Aborted

[JoeCFD]

@buhtz said in Could not load the Qt platform plugin "xcb" in "" even though it was found.":

libqxcb.so

First, /home/user/ is not a good location. I guess you have /opt dir and install the package over there. When you install your package, you may have options for location.
Second, try:
ldd /home/user/.local/lib/python3.9/site-packages/PyQt6/Qt6/plugins/platforms/libqxcb.so
to see if its all dependencies are available. If one of its dependencies is not installed, it can not be loaded. It is likely that xcb libs are not installed.
On my computer, the following libs are needed for libqxcb.so

libX11-xcb.so.1 => /usr/lib/x86_64-linux-gnu/libX11-xcb.so.1 (0x00007f2f41c45000)
libxcb-icccm.so.4 => /usr/lib/x86_64-linux-gnu/libxcb-icccm.so.4 (0x00007f2f41a40000)
libxcb-image.so.0 => /usr/lib/x86_64-linux-gnu/libxcb-image.so.0 (0x00007f2f4183b000)
libxcb-shm.so.0 => /usr/lib/x86_64-linux-gnu/libxcb-shm.so.0 (0x00007f2f41638000)
libxcb-util.so.1 => /usr/lib/x86_64-linux-gnu/libxcb-util.so.1 (0x00007f2f41432000)
libxcb-keysyms.so.1 => /usr/lib/x86_64-linux-gnu/libxcb-keysyms.so.1 (0x00007f2f4122f000)
libxcb-randr.so.0 => /usr/lib/x86_64-linux-gnu/libxcb-randr.so.0 (0x00007f2f4101f000)
libxcb-render-util.so.0 => /usr/lib/x86_64-linux-gnu/libxcb-render-util.so.0 (0x00007f2f40e1b000)
libxcb-render.so.0 => /usr/lib/x86_64-linux-gnu/libxcb-render.so.0 (0x00007f2f40c0e000)
libxcb-shape.so.0 => /usr/lib/x86_64-linux-gnu/libxcb-shape.so.0 (0x00007f2f40a0a000)
libxcb-sync.so.1 => /usr/lib/x86_64-linux-gnu/libxcb-sync.so.1 (0x00007f2f40803000)
libxcb-xfixes.so.0 => /usr/lib/x86_64-linux-gnu/libxcb-xfixes.so.0 (0x00007f2f405fb000)
libxcb-xinerama.so.0 => /usr/lib/x86_64-linux-gnu/libxcb-xinerama.so.0 (0x00007f2f403f8000)
libxcb-xkb.so.1 => /usr/lib/x86_64-linux-gnu/libxcb-xkb.so.1 (0x00007f2f401dc000)
libxcb.so.1 => /usr/lib/x86_64-linux-gnu/libxcb.so.1 (0x00007f2f3ffb4000)
libXext.so.6 => /usr/lib/x86_64-linux-gnu/libXext.so.6 (0x00007f2f3fda2000)
libX11.so.6 => /usr/lib/x86_64-linux-gnu/libX11.so.6 (0x00007f2f3fa6a000)

[buhtz]

This post is deleted!

[buhtz]

libqxcb.so

First, /home/user/ is not a good location. I guess you have /opt dir and install the package over there. When you install your package, you may have options for location.

I don't have "options for location". PyQt6 was installed from PyPi via python3 -m pip install PyQt6.

I'm the maintainer of a PyQt using GUI application. And I have to think about how my users deal with things like this. Usually they should be able to install everything via there GNU/Linux distribution repository. But in Debian 11 PyQt6 is not available as a Debian package but only via PyPi. Using PyPi is the "maximum" I can ask my users for. Modifying install locations or building themself is not an option here. ;)

I still don't understand what that plugin is for and who is responsible. It resists in the PyQt6 install folder. Why? Isn't it related to vanilla Qt and not to its Python binding?

Second, try:
ldd /home/user/.local/lib/python3.9/site-packages/PyQt6/Qt6/plugins/platforms/libqxcb.so

	linux-vdso.so.1 (0x00007ffd0d7fe000)
	libQt6XcbQpa.so.6 => /home/user/.local/lib/python3.9/site-packages/PyQt6/Qt6/plugins/platforms/../../lib/libQt6XcbQpa.so.6 (0x00007f8a2c277000)
	libxkbcommon-x11.so.0 => /usr/lib/x86_64-linux-gnu/libxkbcommon-x11.so.0 (0x00007f8a2c23a000)
	libxkbcommon.so.0 => /usr/lib/x86_64-linux-gnu/libxkbcommon.so.0 (0x00007f8a2c1f7000)
	libxcb-cursor.so.0 => not found
	libxcb-icccm.so.4 => /usr/lib/x86_64-linux-gnu/libxcb-icccm.so.4 (0x00007f8a2c1f0000)
	libxcb-image.so.0 => /usr/lib/x86_64-linux-gnu/libxcb-image.so.0 (0x00007f8a2c1ea000)
	libxcb-keysyms.so.1 => /usr/lib/x86_64-linux-gnu/libxcb-keysyms.so.1 (0x00007f8a2bfe5000)
	libxcb-randr.so.0 => /usr/lib/x86_64-linux-gnu/libxcb-randr.so.0 (0x00007f8a2bfd3000)
	libxcb-render-util.so.0 => /usr/lib/x86_64-linux-gnu/libxcb-render-util.so.0 (0x00007f8a2bdcf000)
	libxcb-shm.so.0 => /usr/lib/x86_64-linux-gnu/libxcb-shm.so.0 (0x00007f8a2bdca000)
	libxcb-sync.so.1 => /usr/lib/x86_64-linux-gnu/libxcb-sync.so.1 (0x00007f8a2bdc0000)
	libxcb-xfixes.so.0 => /usr/lib/x86_64-linux-gnu/libxcb-xfixes.so.0 (0x00007f8a2bdb6000)
	libxcb-render.so.0 => /usr/lib/x86_64-linux-gnu/libxcb-render.so.0 (0x00007f8a2bda5000)
	libxcb-shape.so.0 => /usr/lib/x86_64-linux-gnu/libxcb-shape.so.0 (0x00007f8a2bda0000)
	libxcb-xkb.so.1 => /usr/lib/x86_64-linux-gnu/libxcb-xkb.so.1 (0x00007f8a2bd82000)
	libxcb.so.1 => /usr/lib/x86_64-linux-gnu/libxcb.so.1 (0x00007f8a2bd57000)
	libQt6OpenGL.so.6 => /home/user/.local/lib/python3.9/site-packages/PyQt6/Qt6/plugins/platforms/../../lib/libQt6OpenGL.so.6 (0x00007f8a2bcb5000)
	libQt6Gui.so.6 => /home/user/.local/lib/python3.9/site-packages/PyQt6/Qt6/plugins/platforms/../../lib/libQt6Gui.so.6 (0x00007f8a2b2f3000)
	libGL.so.1 => /usr/lib/x86_64-linux-gnu/libGL.so.1 (0x00007f8a2b26a000)
	libQt6Core.so.6 => /home/user/.local/lib/python3.9/site-packages/PyQt6/Qt6/plugins/platforms/../../lib/libQt6Core.so.6 (0x00007f8a2abe1000)
	libX11-xcb.so.1 => /usr/lib/x86_64-linux-gnu/libX11-xcb.so.1 (0x00007f8a2abdc000)
	libX11.so.6 => /usr/lib/x86_64-linux-gnu/libX11.so.6 (0x00007f8a2aa99000)
	libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f8a2aa93000)
	libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f8a2aa71000)
	libstdc++.so.6 => /usr/lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007f8a2a8a2000)
	libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f8a2a75e000)
	libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007f8a2a744000)
	libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f8a2a570000)
	libxcb-cursor.so.0 => not found
	libglib-2.0.so.0 => /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0 (0x00007f8a2a441000)
	libgthread-2.0.so.0 => /usr/lib/x86_64-linux-gnu/libgthread-2.0.so.0 (0x00007f8a2a43a000)
	libxcb-util.so.1 => /usr/lib/x86_64-linux-gnu/libxcb-util.so.1 (0x00007f8a2a432000)
	libXau.so.6 => /usr/lib/x86_64-linux-gnu/libXau.so.6 (0x00007f8a2a42d000)
	libXdmcp.so.6 => /usr/lib/x86_64-linux-gnu/libXdmcp.so.6 (0x00007f8a2a227000)
	libEGL.so.1 => /usr/lib/x86_64-linux-gnu/libEGL.so.1 (0x00007f8a2a212000)
	libfontconfig.so.1 => /usr/lib/x86_64-linux-gnu/libfontconfig.so.1 (0x00007f8a2a1ca000)
	libQt6DBus.so.6 => /home/user/.local/lib/python3.9/site-packages/PyQt6/Qt6/plugins/platforms/../../lib/libQt6DBus.so.6 (0x00007f8a2a104000)
	libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007f8a2a0e7000)
	libfreetype.so.6 => /usr/lib/x86_64-linux-gnu/libfreetype.so.6 (0x00007f8a2a024000)
	libGLdispatch.so.0 => /usr/lib/x86_64-linux-gnu/libGLdispatch.so.0 (0x00007f8a29f6c000)
	libGLX.so.0 => /usr/lib/x86_64-linux-gnu/libGLX.so.0 (0x00007f8a29f38000)
	libicui18n.so.56 => /home/user/.local/lib/python3.9/site-packages/PyQt6/Qt6/plugins/platforms/../../lib/libicui18n.so.56 (0x00007f8a29a9d000)
	libicuuc.so.56 => /home/user/.local/lib/python3.9/site-packages/PyQt6/Qt6/plugins/platforms/../../lib/libicuuc.so.56 (0x00007f8a296e5000)
	libicudata.so.56 => /home/user/.local/lib/python3.9/site-packages/PyQt6/Qt6/plugins/platforms/../../lib/libicudata.so.56 (0x00007f8a27d02000)
	librt.so.1 => /lib/x86_64-linux-gnu/librt.so.1 (0x00007f8a27cf8000)
	/lib64/ld-linux-x86-64.so.2 (0x00007f8a2c331000)
	libpcre.so.3 => /lib/x86_64-linux-gnu/libpcre.so.3 (0x00007f8a27c85000)
	libbsd.so.0 => /usr/lib/x86_64-linux-gnu/libbsd.so.0 (0x00007f8a27c6c000)
	libexpat.so.1 => /lib/x86_64-linux-gnu/libexpat.so.1 (0x00007f8a27c3d000)
	libuuid.so.1 => /usr/lib/x86_64-linux-gnu/libuuid.so.1 (0x00007f8a27c34000)
	libdbus-1.so.3 => /lib/x86_64-linux-gnu/libdbus-1.so.3 (0x00007f8a27bdf000)
	libpng16.so.16 => /usr/lib/x86_64-linux-gnu/libpng16.so.16 (0x00007f8a27ba5000)
	libbrotlidec.so.1 => /usr/lib/x86_64-linux-gnu/libbrotlidec.so.1 (0x00007f8a27b95000)
	libmd.so.0 => /usr/lib/x86_64-linux-gnu/libmd.so.0 (0x00007f8a27b88000)
	libsystemd.so.0 => /usr/lib/x86_64-linux-gnu/libsystemd.so.0 (0x00007f8a27ad3000)
	libbrotlicommon.so.1 => /usr/lib/x86_64-linux-gnu/libbrotlicommon.so.1 (0x00007f8a27ab0000)
	liblzma.so.5 => /lib/x86_64-linux-gnu/liblzma.so.5 (0x00007f8a27a88000)
	libzstd.so.1 => /usr/lib/x86_64-linux-gnu/libzstd.so.1 (0x00007f8a279ad000)
	liblz4.so.1 => /usr/lib/x86_64-linux-gnu/liblz4.so.1 (0x00007f8a27988000)
	libgcrypt.so.20 => /usr/lib/x86_64-linux-gnu/libgcrypt.so.20 (0x00007f8a27868000)
	libgpg-error.so.0 => /lib/x86_64-linux-gnu/libgpg-error.so.0 (0x00007f8a27842000)

[JoeCFD]

@buhtz said in Could not load the Qt platform plugin "xcb" in "" even though it was found.":

do not know anything about python. /home/user/.local/ does not look good.

libxcb-cursor.so.0 => not found

this one libxcb-cursor.so.0 is not installed.
sudo apt-get install -y libxcb-cursor-dev or
sudo apt-get install -y libxcb-cursor is good enough.

think a plugin is similar to a dynamically linked lib. But your app does not need to be linked to it in building, instead loads it at running time. Sure your app has to know its path. In Qt, its path is set for your app if qt path is known.

[buhtz]

That solved the problem.
Thanks a lot for helping me and investing your time.

[Ikaros]

@JoeCFD thank u so much!

[-Salih123]

@buhtz
hello buhtz
I also had a similar problem
I get this error after transferring the codes to my own computer at the end of a project I carried out jointly with my friend.

QObject::moveToThread: The current thread (0x25c9e90) is not the object's thread (0x2dfe0e0).
Cannot move to target array (0x25c9e90)

qt.qpa.plugin: Could not load Qt platform plugin "xcb" in "/usr/local/lib/python3.8/dist-packages/cv2/qt/plugins" even though it is present.
This application failed to start because no Qt platform plug-ins could be started. Reinstalling the app may fix this problem.

Available platform plugins are: xcb, eglfs, linuxfb, minimal, minimalegl, offscreen, vnc, wayland-egl, wayland, wayland-xcomposite-egl, wayland-xcomposite-glx, webgl.

Canceled (core dumped)

Can you elaborate a little more on how you solved it?

[Pl45m4]

@Salih123 said in Could not load the Qt platform plugin "xcb" in "" even though it was found.":

QObject::moveToThread: The current thread (0x25c9e90) is not the object's thread (0x2dfe0e0).
Cannot move to target array (0x25c9e90)

This indicates that there's something wrong in your code. You are probably moving some QObjects from/to a thread.

Can you elaborate a little more on how you solved it?

Have you tried to install what @buhtz posted above?

[saundecp]

Leaving a comment here because this was a top result when I had the exact error. In my case, I had pip installed opencv, and that pip-installed version had conflicts with the system qt. Steps that ultimately resolved the problem are here on Stack Overflow.