qt.qpa.plugin: Could not load the Qt platform plugin "xcb"

Puddies

When starting my python application using qt, it instantly crashes with the following message.

QObject::moveToThread: Current thread (0x55f3a9a0e230) is not the object's thread (0x55f3a9c9a160).
Cannot move to target thread (0x55f3a9a0e230)

qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "/home/...<username>.../.local/lib/python3.9/site-packages/cv2/qt/plugins" 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, eglfs, linuxfb, minimal, minimalegl, offscreen, vnc, wayland-egl, wayland, wayland-xcomposite-egl, wayland-xcomposite-glx.

I am on manjaro linux.
I already reinstalled libxcb and qt5-base, which did not help.

Any ideas how to fix this?

jsulm

@Puddies Set QT_DEBUG_PLUGINS before starting your app and check the output, or post it here.

Puddies

The output has 15543 lines. I am not allowed to post a text with that length here. Can I append a text file here?

The output starts with

QFactoryLoader::QFactoryLoader() checking directory path "/home/<username>/.local/lib/python3.9/site-packages/cv2/qt/plugins" ...
QFactoryLoader::QFactoryLoader() checking directory path "/usr/lib/qt/plugins" ...
QFactoryLoader::QFactoryLoader() looking at "/usr/lib/qt/plugins/ownclouddolphinactionplugin.so"
Found metadata in lib /usr/lib/qt/plugins/ownclouddolphinactionplugin.so, metadata=
{
    "IID": "org.kde.KPluginFactory",
    "archreq": 0,
    "className": "OwncloudDolphinPluginActionFactory",
    "debug": false,
    "version": 331520
}


Got keys from plugin meta data ()
QFactoryLoader::QFactoryLoader() looking at "/usr/lib/qt/plugins/owncloudsync_vfs_suffix.so"
Found metadata in lib /usr/lib/qt/plugins/owncloudsync_vfs_suffix.so, metadata=
{
    "IID": "org.owncloud.PluginFactory",
    "MetaData": {
        "type": "vfs",
        "version": "2.8.2"
    },
    "archreq": 0,
    "className": "SuffixVfsPluginFactory",
    "debug": false,
    "version": 331520
}

and it ends with

QFactoryLoader::QFactoryLoader() checking directory path "/home/<username>/.local/lib/python3.9/site-packages/cv2/qt/plugins" ...
QFactoryLoader::QFactoryLoader() checking directory path "/usr/lib/qt/plugins" ...
QFactoryLoader::QFactoryLoader() looking at "/usr/lib/qt/plugins/ownclouddolphinactionplugin.so"
Found metadata in lib /usr/lib/qt/plugins/ownclouddolphinactionplugin.so, metadata=
{
    "IID": "org.kde.KPluginFactory",
    "archreq": 0,
    "className": "OwncloudDolphinPluginActionFactory",
    "debug": false,
    "version": 331520
}


Got keys from plugin meta data ()
QFactoryLoader::QFactoryLoader() looking at "/usr/lib/qt/plugins/owncloudsync_vfs_suffix.so"
Found metadata in lib /usr/lib/qt/plugins/owncloudsync_vfs_suffix.so, metadata=
{
    "IID": "org.owncloud.PluginFactory",
    "MetaData": {
        "type": "vfs",
        "version": "2.8.2"
    },
    "archreq": 0,
    "className": "SuffixVfsPluginFactory",
    "debug": false,
    "version": 331520
}

I dont know, if that helps.

jsulm

@Puddies said in qt.qpa.plugin: Could not load the Qt platform plugin "xcb":

I dont know, if that helps.

It does not. Please post whole output or at least the part where xcb platform plug-in is loaded...

Puddies

I am very sorry, but I had to upload the output to my dropbox. I am not able to post a text with more than about 32000 characters here.

Here is the link with the full output:
https://www.dropbox.com/s/k8eahgu3neesxe6/output.txt?dl=0

Puddies

Ok, I have found the xcb part. Maybe this helps a bit:

QFactoryLoader::QFactoryLoader() checking directory path "/home/<username>/.local/lib/python3.9/site-packages/cv2/qt/plugins/platforms" ...
QFactoryLoader::QFactoryLoader() looking at "/home/<username>/.local/lib/python3.9/site-packages/cv2/qt/plugins/platforms/libqxcb.so"
Found metadata in lib /home/<username>/.local/lib/python3.9/site-packages/cv2/qt/plugins/platforms/libqxcb.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "xcb"
        ]
    },
    "archreq": 0,
    "className": "QXcbIntegrationPlugin",
    "debug": false,
    "version": 331520
}


Got keys from plugin meta data ("xcb")
QFactoryLoader::QFactoryLoader() checking directory path "/usr/lib/qt/plugins/platforms" ...
QFactoryLoader::QFactoryLoader() looking at "/usr/lib/qt/plugins/platforms/libqeglfs.so"
Found metadata in lib /usr/lib/qt/plugins/platforms/libqeglfs.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "eglfs"
        ]
    },
    "archreq": 0,
    "className": "QEglFSIntegrationPlugin",
    "debug": false,
    "version": 331520
}


Got keys from plugin meta data ("eglfs")
QFactoryLoader::QFactoryLoader() looking at "/usr/lib/qt/plugins/platforms/libqlinuxfb.so"
Found metadata in lib /usr/lib/qt/plugins/platforms/libqlinuxfb.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "linuxfb"
        ]
    },
    "archreq": 0,
    "className": "QLinuxFbIntegrationPlugin",
    "debug": false,
    "version": 331520
}


Got keys from plugin meta data ("linuxfb")
QFactoryLoader::QFactoryLoader() looking at "/usr/lib/qt/plugins/platforms/libqminimal.so"
Found metadata in lib /usr/lib/qt/plugins/platforms/libqminimal.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "minimal"
        ]
    },
    "archreq": 0,
    "className": "QMinimalIntegrationPlugin",
    "debug": false,
    "version": 331520
}


Got keys from plugin meta data ("minimal")
QFactoryLoader::QFactoryLoader() looking at "/usr/lib/qt/plugins/platforms/libqminimalegl.so"
Found metadata in lib /usr/lib/qt/plugins/platforms/libqminimalegl.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "minimalegl"
        ]
    },
    "archreq": 0,
    "className": "QMinimalEglIntegrationPlugin",
    "debug": false,
    "version": 331520
}


Got keys from plugin meta data ("minimalegl")
QFactoryLoader::QFactoryLoader() looking at "/usr/lib/qt/plugins/platforms/libqoffscreen.so"
Found metadata in lib /usr/lib/qt/plugins/platforms/libqoffscreen.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "offscreen"
        ]
    },
    "archreq": 0,
    "className": "QOffscreenIntegrationPlugin",
    "debug": false,
    "version": 331520
}


Got keys from plugin meta data ("offscreen")
QFactoryLoader::QFactoryLoader() looking at "/usr/lib/qt/plugins/platforms/libqvnc.so"
Found metadata in lib /usr/lib/qt/plugins/platforms/libqvnc.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "vnc"
        ]
    },
    "archreq": 0,
    "className": "QVncIntegrationPlugin",
    "debug": false,
    "version": 331520
}


Got keys from plugin meta data ("vnc")
QFactoryLoader::QFactoryLoader() looking at "/usr/lib/qt/plugins/platforms/libqwayland-egl.so"
Found metadata in lib /usr/lib/qt/plugins/platforms/libqwayland-egl.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "wayland-egl"
        ]
    },
    "archreq": 0,
    "className": "QWaylandEglPlatformIntegrationPlugin",
    "debug": false,
    "version": 331520
}


Got keys from plugin meta data ("wayland-egl")
QFactoryLoader::QFactoryLoader() looking at "/usr/lib/qt/plugins/platforms/libqwayland-generic.so"
Found metadata in lib /usr/lib/qt/plugins/platforms/libqwayland-generic.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "wayland"
        ]
    },
    "archreq": 0,
    "className": "QWaylandIntegrationPlugin",
    "debug": false,
    "version": 331520
}


Got keys from plugin meta data ("wayland")
QFactoryLoader::QFactoryLoader() looking at "/usr/lib/qt/plugins/platforms/libqwayland-xcomposite-egl.so"
Found metadata in lib /usr/lib/qt/plugins/platforms/libqwayland-xcomposite-egl.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "wayland-xcomposite-egl"
        ]
    },
    "archreq": 0,
    "className": "QWaylandXCompositeEglPlatformIntegrationPlugin",
    "debug": false,
    "version": 331520
}


Got keys from plugin meta data ("wayland-xcomposite-egl")
QFactoryLoader::QFactoryLoader() looking at "/usr/lib/qt/plugins/platforms/libqwayland-xcomposite-glx.so"
Found metadata in lib /usr/lib/qt/plugins/platforms/libqwayland-xcomposite-glx.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "wayland-xcomposite-glx"
        ]
    },
    "archreq": 0,
    "className": "QWaylandXCompositeGlxPlatformIntegrationPlugin",
    "debug": false,
    "version": 331520
}


Got keys from plugin meta data ("wayland-xcomposite-glx")
QFactoryLoader::QFactoryLoader() looking at "/usr/lib/qt/plugins/platforms/libqxcb.so"
Found metadata in lib /usr/lib/qt/plugins/platforms/libqxcb.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "xcb"
        ]
    },
    "archreq": 0,
    "className": "QXcbIntegrationPlugin",
    "debug": false,
    "version": 331520
}


Got keys from plugin meta data ("xcb")
QFactoryLoader::QFactoryLoader() checking directory path "/usr/bin/platforms" ...
loaded library "/home/<username>/.local/lib/python3.9/site-packages/cv2/qt/plugins/platforms/libqxcb.so"
QObject::moveToThread: Current thread (0x55871b6fa2c0) is not the object's thread (0x55871b6bee30).
Cannot move to target thread (0x55871b6fa2c0)

qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "/home/<username>/.local/lib/python3.9/site-packages/cv2/qt/plugins" 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, eglfs, linuxfb, minimal, minimalegl, offscreen, vnc, wayland-egl, wayland, wayland-xcomposite-egl, wayland-xcomposite-glx.

JonB

@Puddies
Try

ldd /home/<username>/.local/lib/python3.9/site-packages/cv2/qt/plugins/platforms/libqxcb.so

Any "not found"s?

Puddies

@JonB

ldd: Warnung: Sie haben kein Ausführungsrecht für `/home/<username>/.local/lib/python3.9/site-packages/cv2/qt/plugins/platforms/libqxcb.so'
	linux-vdso.so.1 (0x00007ffe5aac9000)
	libQt5XcbQpa-70670cdb.so.5.15.0 => /home/<username>/.local/lib/python3.9/site-packages/cv2/qt/plugins/platforms/../../../../opencv_python.libs/libQt5XcbQpa-70670cdb.so.5.15.0 (0x00007f53138ac000)
	libfreetype-8d3bcff4.so.6.14.0 => /home/<username>/.local/lib/python3.9/site-packages/cv2/qt/plugins/platforms/../../../../opencv_python.libs/libfreetype-8d3bcff4.so.6.14.0 (0x00007f53135dc000)
	libz-d8a329de.so.1.2.7 => /home/<username>/.local/lib/python3.9/site-packages/cv2/qt/plugins/platforms/../../../../opencv_python.libs/libz-d8a329de.so.1.2.7 (0x00007f53133c5000)
	libQt5Gui-ca084835.so.5.15.0 => /home/<username>/.local/lib/python3.9/site-packages/cv2/qt/plugins/platforms/../../../../opencv_python.libs/libQt5Gui-ca084835.so.5.15.0 (0x00007f5312a2e000)
	libQt5Core-d92f2856.so.5.15.0 => /home/<username>/.local/lib/python3.9/site-packages/cv2/qt/plugins/platforms/../../../../opencv_python.libs/libQt5Core-d92f2856.so.5.15.0 (0x00007f53122d4000)
	libGL.so.1 => /usr/lib/libGL.so.1 (0x00007f531224e000)
	libpthread.so.0 => /usr/lib/libpthread.so.0 (0x00007f531222d000)
	libX11-xcb-1ae4fd0e.so.1.0.0 => /home/<username>/.local/lib/python3.9/site-packages/cv2/qt/plugins/platforms/../../../../opencv_python.libs/libX11-xcb-1ae4fd0e.so.1.0.0 (0x00007f531202a000)
	libxcb-icccm-413c9f41.so.4.0.0 => /home/<username>/.local/lib/python3.9/site-packages/cv2/qt/plugins/platforms/../../../../opencv_python.libs/libxcb-icccm-413c9f41.so.4.0.0 (0x00007f5311e24000)
	libxcb-image-e82a276d.so.0.0.0 => /home/<username>/.local/lib/python3.9/site-packages/cv2/qt/plugins/platforms/../../../../opencv_python.libs/libxcb-image-e82a276d.so.0.0.0 (0x00007f5311c1a000)
	libxcb-shm-7a199f70.so.0.0.0 => /home/<username>/.local/lib/python3.9/site-packages/cv2/qt/plugins/platforms/../../../../opencv_python.libs/libxcb-shm-7a199f70.so.0.0.0 (0x00007f5311a14000)
	libxcb-keysyms-21015570.so.1.0.0 => /home/<username>/.local/lib/python3.9/site-packages/cv2/qt/plugins/platforms/../../../../opencv_python.libs/libxcb-keysyms-21015570.so.1.0.0 (0x00007f5311810000)
	libxcb-randr-a96a5a87.so.0.1.0 => /home/<username>/.local/lib/python3.9/site-packages/cv2/qt/plugins/platforms/../../../../opencv_python.libs/libxcb-randr-a96a5a87.so.0.1.0 (0x00007f53115f9000)
	libxcb-render-util-43ce00f5.so.0.0.0 => /home/<username>/.local/lib/python3.9/site-packages/cv2/qt/plugins/platforms/../../../../opencv_python.libs/libxcb-render-util-43ce00f5.so.0.0.0 (0x00007f53113f3000)
	libxcb-render-637b984a.so.0.0.0 => /home/<username>/.local/lib/python3.9/site-packages/cv2/qt/plugins/platforms/../../../../opencv_python.libs/libxcb-render-637b984a.so.0.0.0 (0x00007f53111dd000)
	libxcb-shape-25c2b258.so.0.0.0 => /home/<username>/.local/lib/python3.9/site-packages/cv2/qt/plugins/platforms/../../../../opencv_python.libs/libxcb-shape-25c2b258.so.0.0.0 (0x00007f5310fd7000)
	libxcb-sync-89374f40.so.1.0.0 => /home/<username>/.local/lib/python3.9/site-packages/cv2/qt/plugins/platforms/../../../../opencv_python.libs/libxcb-sync-89374f40.so.1.0.0 (0x00007f5310dce000)
	libxcb-xfixes-9be3ba6f.so.0.0.0 => /home/<username>/.local/lib/python3.9/site-packages/cv2/qt/plugins/platforms/../../../../opencv_python.libs/libxcb-xfixes-9be3ba6f.so.0.0.0 (0x00007f5310bc2000)
	libxcb-xinerama-ae147f87.so.0.0.0 => /home/<username>/.local/lib/python3.9/site-packages/cv2/qt/plugins/platforms/../../../../opencv_python.libs/libxcb-xinerama-ae147f87.so.0.0.0 (0x00007f53109bd000)
	libxcb-xkb-9ba31ab3.so.1.0.0 => /home/<username>/.local/lib/python3.9/site-packages/cv2/qt/plugins/platforms/../../../../opencv_python.libs/libxcb-xkb-9ba31ab3.so.1.0.0 (0x00007f5310794000)
	libxcb.so.1 => /usr/lib/libxcb.so.1 (0x00007f531076a000)
	libXext.so.6 => /usr/lib/libXext.so.6 (0x00007f5310755000)
	libX11.so.6 => /usr/lib/libX11.so.6 (0x00007f5310614000)
	libSM.so.6 => /usr/lib/libSM.so.6 (0x00007f531060a000)
	libICE.so.6 => /usr/lib/libICE.so.6 (0x00007f53105ed000)
	libxkbcommon-x11-c65ed502.so.0.0.0 => /home/<username>/.local/lib/python3.9/site-packages/cv2/qt/plugins/platforms/../../../../opencv_python.libs/libxkbcommon-x11-c65ed502.so.0.0.0 (0x00007f53103de000)
	libxkbcommon-71ae2972.so.0.0.0 => /home/<username>/.local/lib/python3.9/site-packages/cv2/qt/plugins/platforms/../../../../opencv_python.libs/libxkbcommon-71ae2972.so.0.0.0 (0x00007f531019d000)
	libdl.so.2 => /usr/lib/libdl.so.2 (0x00007f5310196000)
	libstdc++.so.6 => /usr/lib/libstdc++.so.6 (0x00007f530ff80000)
	libm.so.6 => /usr/lib/libm.so.6 (0x00007f530fe3c000)
	libgcc_s.so.1 => /usr/lib/libgcc_s.so.1 (0x00007f530fe21000)
	libc.so.6 => /usr/lib/libc.so.6 (0x00007f530fc53000)
	libgthread-2.0.so.0 => /usr/lib/libgthread-2.0.so.0 (0x00007f530fc4e000)
	libglib-2.0.so.0 => /usr/lib/libglib-2.0.so.0 (0x00007f530fb19000)
	libbz2-a273e504.so.1.0.6 => /home/<username>/.local/lib/python3.9/site-packages/cv2/qt/plugins/platforms/../../../../opencv_python.libs/libbz2-a273e504.so.1.0.6 (0x00007f530f908000)
	libpng15-c2ffaf3d.so.15.13.0 => /home/<username>/.local/lib/python3.9/site-packages/cv2/qt/plugins/platforms/../../../../opencv_python.libs/libpng15-c2ffaf3d.so.15.13.0 (0x00007f530f6d9000)
	/usr/lib64/ld-linux-x86-64.so.2 (0x00007f5313b5f000)
	libGLdispatch.so.0 => /usr/lib/libGLdispatch.so.0 (0x00007f530f61f000)
	libGLX.so.0 => /usr/lib/libGLX.so.0 (0x00007f530f5ec000)
	libxcb-util-4d666913.so.1.0.0 => /home/<username>/.local/lib/python3.9/site-packages/cv2/qt/plugins/platforms/../../../../opencv_python.libs/libxcb-util-4d666913.so.1.0.0 (0x00007f530f3e5000)
	libXau-00ec42fe.so.6.0.0 => /home/<username>/.local/lib/python3.9/site-packages/cv2/qt/plugins/platforms/../../../../opencv_python.libs/libXau-00ec42fe.so.6.0.0 (0x00007f530f1e0000)
	libXau.so.6 => /usr/lib/libXau.so.6 (0x00007f530f1d9000)
	libXdmcp.so.6 => /usr/lib/libXdmcp.so.6 (0x00007f530f1d1000)
	libuuid.so.1 => /usr/lib/libuuid.so.1 (0x00007f530f1c8000)
	libpcre.so.1 => /usr/lib/libpcre.so.1 (0x00007f530f156000)

JonB

@Puddies said in qt.qpa.plugin: Could not load the Qt platform plugin "xcb":

ldd: Warnung: Sie haben kein Ausführungsrecht für /home/<username>/.local/lib/python3.9/site-packages/cv2/qt/plugins/platforms/libqxcb.so'`

The dependencies look OK, but never seen this warning before. What does ls -l on it tell you?

Having said that, it did report

loaded library "/home/<username>/.local/lib/python3.9/site-packages/cv2/qt/plugins/platforms/libqxcb.so"

I would be looking at the

QObject::moveToThread: Current thread (0x55871b6fa2c0) is not the object's thread (0x55871b6bee30).
Cannot move to target thread (0x55871b6fa2c0)

You should not be getting this. Are you playing with threads somewhere?

Pl45m4

@Puddies said in qt.qpa.plugin: Could not load the Qt platform plugin "xcb":

ldd: Warnung: Sie haben kein Ausführungsrecht für `/home/<username>/.local/lib/python3.9/site-packages/cv2/qt/plugins/platforms/libqxcb.so'

Check your permissons on this directory. It expects execution permission. Seems strange.

@JonB It says "ldd: warning: you do not have execution permission for...."

Puddies

@JonB
ls -l returns
-rw-r--r-- 1 <username> <group> 104K 10. Jun 13:34 libqxcb.so

I set execution permissions and the warning disappeared. However, this did not resolve the crash of my application.

I dont use any threads in my code. However, I dont also use QT directly, I use matplotlib for the gui (which uses qt).
But I did not explicitely use threads here.

JonB

@Puddies
Normally under Linux .so files are marked executable, so would be -rwxr-xr-x. That will be the cause of the warning message. But it doesn't actually matter, since it says it loaded it.

I still think you have a threading issue as per the message, I don't know if that is what is causing your problem.

JonB

Thread https://forum.qt.io/topic/127832/pyqt5-and-tensorflowlite-causes-crashes/3 shows exactly the same output and issue. If someone can answer one it answers the other....

bimhox

Was someone successful in fixing it? worst case scenario, should we disintall and reinstall what application? qt ? cv2? python?

jerryhon

This post is deleted!