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#1 2019-06-11 16:34:54

joanmanel
Member
Registered: 2012-11-06
Posts: 141

PyQt5 fails to load Could not load the Qt platform plugin "xcb"

I have PyQt5 installed and I am running an application using it. I am using a virtualenv and everything was installed with pip.

When I try to launch it I receive the following error:

WARNING: Could not load the Qt platform plugin "xcb" in "" even though it was found.
WARNING: 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, wayland-egl, wayland, wayland-xcomposite-egl, wayland-xcomposite-glx, webgl, xcb.

Aborted (core dumped)

Trying to debug it with export QT_DEBUG_PLUGINS=1, I get:

WARNING: QFactoryLoader::QFactoryLoader() checking directory path "/home/juanma/Projects/ChemCAD/ChemCAD/venv/lib/python3.7/site-packages/PyQt5/Qt/plugins/platforms" ...
WARNING: QFactoryLoader::QFactoryLoader() looking at "/home/juanma/Projects/ChemCAD/ChemCAD/venv/lib/python3.7/site-packages/PyQt5/Qt/plugins/platforms/libqeglfs.so"
WARNING: Found metadata in lib /home/juanma/Projects/ChemCAD/ChemCAD/venv/lib/python3.7/site-packages/PyQt5/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": 330752
}


WARNING: Got keys from plugin meta data ("eglfs")
WARNING: QFactoryLoader::QFactoryLoader() looking at "/home/juanma/Projects/ChemCAD/ChemCAD/venv/lib/python3.7/site-packages/PyQt5/Qt/plugins/platforms/libqlinuxfb.so"
WARNING: Found metadata in lib /home/juanma/Projects/ChemCAD/ChemCAD/venv/lib/python3.7/site-packages/PyQt5/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": 330752
}


WARNING: Got keys from plugin meta data ("linuxfb")
WARNING: QFactoryLoader::QFactoryLoader() looking at "/home/juanma/Projects/ChemCAD/ChemCAD/venv/lib/python3.7/site-packages/PyQt5/Qt/plugins/platforms/libqminimal.so"
WARNING: Found metadata in lib /home/juanma/Projects/ChemCAD/ChemCAD/venv/lib/python3.7/site-packages/PyQt5/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": 330752
}


WARNING: Got keys from plugin meta data ("minimal")
WARNING: QFactoryLoader::QFactoryLoader() looking at "/home/juanma/Projects/ChemCAD/ChemCAD/venv/lib/python3.7/site-packages/PyQt5/Qt/plugins/platforms/libqminimalegl.so"
WARNING: Found metadata in lib /home/juanma/Projects/ChemCAD/ChemCAD/venv/lib/python3.7/site-packages/PyQt5/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": 330752
}


WARNING: Got keys from plugin meta data ("minimalegl")
WARNING: QFactoryLoader::QFactoryLoader() looking at "/home/juanma/Projects/ChemCAD/ChemCAD/venv/lib/python3.7/site-packages/PyQt5/Qt/plugins/platforms/libqoffscreen.so"
WARNING: Found metadata in lib /home/juanma/Projects/ChemCAD/ChemCAD/venv/lib/python3.7/site-packages/PyQt5/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": 330752
}


WARNING: Got keys from plugin meta data ("offscreen")
WARNING: QFactoryLoader::QFactoryLoader() looking at "/home/juanma/Projects/ChemCAD/ChemCAD/venv/lib/python3.7/site-packages/PyQt5/Qt/plugins/platforms/libqvnc.so"
WARNING: Found metadata in lib /home/juanma/Projects/ChemCAD/ChemCAD/venv/lib/python3.7/site-packages/PyQt5/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": 330752
}


WARNING: Got keys from plugin meta data ("vnc")
WARNING: QFactoryLoader::QFactoryLoader() looking at "/home/juanma/Projects/ChemCAD/ChemCAD/venv/lib/python3.7/site-packages/PyQt5/Qt/plugins/platforms/libqwayland-egl.so"
WARNING: Found metadata in lib /home/juanma/Projects/ChemCAD/ChemCAD/venv/lib/python3.7/site-packages/PyQt5/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": 330752
}


WARNING: Got keys from plugin meta data ("wayland-egl")
WARNING: QFactoryLoader::QFactoryLoader() looking at "/home/juanma/Projects/ChemCAD/ChemCAD/venv/lib/python3.7/site-packages/PyQt5/Qt/plugins/platforms/libqwayland-generic.so"
WARNING: Found metadata in lib /home/juanma/Projects/ChemCAD/ChemCAD/venv/lib/python3.7/site-packages/PyQt5/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": 330752
}


WARNING: Got keys from plugin meta data ("wayland")
WARNING: QFactoryLoader::QFactoryLoader() looking at "/home/juanma/Projects/ChemCAD/ChemCAD/venv/lib/python3.7/site-packages/PyQt5/Qt/plugins/platforms/libqwayland-xcomposite-egl.so"
WARNING: Found metadata in lib /home/juanma/Projects/ChemCAD/ChemCAD/venv/lib/python3.7/site-packages/PyQt5/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": 330752
}


WARNING: Got keys from plugin meta data ("wayland-xcomposite-egl")
WARNING: QFactoryLoader::QFactoryLoader() looking at "/home/juanma/Projects/ChemCAD/ChemCAD/venv/lib/python3.7/site-packages/PyQt5/Qt/plugins/platforms/libqwayland-xcomposite-glx.so"
WARNING: Found metadata in lib /home/juanma/Projects/ChemCAD/ChemCAD/venv/lib/python3.7/site-packages/PyQt5/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": 330752
}


WARNING: Got keys from plugin meta data ("wayland-xcomposite-glx")
WARNING: QFactoryLoader::QFactoryLoader() looking at "/home/juanma/Projects/ChemCAD/ChemCAD/venv/lib/python3.7/site-packages/PyQt5/Qt/plugins/platforms/libqwebgl.so"
WARNING: Found metadata in lib /home/juanma/Projects/ChemCAD/ChemCAD/venv/lib/python3.7/site-packages/PyQt5/Qt/plugins/platforms/libqwebgl.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "webgl"
        ]
    },
    "archreq": 0,
    "className": "QWebGLIntegrationPlugin",
    "debug": false,
    "version": 330752
}


WARNING: Got keys from plugin meta data ("webgl")
WARNING: QFactoryLoader::QFactoryLoader() looking at "/home/juanma/Projects/ChemCAD/ChemCAD/venv/lib/python3.7/site-packages/PyQt5/Qt/plugins/platforms/libqxcb.so"
WARNING: Found metadata in lib /home/juanma/Projects/ChemCAD/ChemCAD/venv/lib/python3.7/site-packages/PyQt5/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": 330752
}


WARNING: Got keys from plugin meta data ("xcb")
WARNING: QFactoryLoader::QFactoryLoader() checking directory path "/usr/bin/platforms" ...
WARNING: Cannot load library /home/juanma/Projects/ChemCAD/ChemCAD/venv/lib/python3.7/site-packages/PyQt5/Qt/plugins/platforms/libqxcb.so: (/lib/libQt5XcbQpa.so.5: symbol _ZTI23QPlatformVulkanInstance version Qt_5_PRIVATE_API not defined in file libQt5Gui.so.5 with link time reference)
WARNING: QLibraryPrivate::loadPlugin failed on "/home/juanma/Projects/ChemCAD/ChemCAD/venv/lib/python3.7/site-packages/PyQt5/Qt/plugins/platforms/libqxcb.so" : "Cannot load library /home/juanma/Projects/ChemCAD/ChemCAD/venv/lib/python3.7/site-packages/PyQt5/Qt/plugins/platforms/libqxcb.so: (/lib/libQt5XcbQpa.so.5: symbol _ZTI23QPlatformVulkanInstance version Qt_5_PRIVATE_API not defined in file libQt5Gui.so.5 with link time reference)"
WARNING: Could not load the Qt platform plugin "xcb" in "" even though it was found.
WARNING: 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, wayland-egl, wayland, wayland-xcomposite-egl, wayland-xcomposite-glx, webgl, xcb.

Aborted (core dumped)

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#2 2019-06-12 10:30:03

Lone_Wolf
Member
From: Netherlands, Europe
Registered: 2005-10-04
Posts: 7,050

Re: PyQt5 fails to load Could not load the Qt platform plugin "xcb"

WARNING: QLibraryPrivate::loadPlugin failed on "/home/juanma/Projects/ChemCAD/ChemCAD/venv/lib/python3.7/site-packages/PyQt5/Qt/plugins/platforms/libqxcb.so" : 
"Cannot load library /home/juanma/Projects/ChemCAD/ChemCAD/venv/lib/python3.7/site-packages/PyQt5/Qt/plugins/platforms/libqxcb.so: (/lib/libQt5XcbQpa.so.5: 
symbol _ZTI23QPlatformVulkanInstance version Qt_5_PRIVATE_API not defined in file libQt5Gui.so.5 with link time reference)"
WARNING: Could not load the Qt platform plugin "xcb" in "" even though it was found.

The qt5_private_api part suggests the application expects an older QT5 version , see https://wiki.archlinux.org/index.php/Qt … Qt5_update

Often this can by solved by setting QT_QPA_PLATFORMTHEME explicitly.

Last edited by Lone_Wolf (2019-06-12 10:32:06)


Multi-init booting with apg Openrc and systemd coexisting
Automounting : not needed, i prefer pmount
Aur helpers : makepkg + my own local repo === rarely need them

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#3 2019-06-12 10:47:14

joanmanel
Member
Registered: 2012-11-06
Posts: 141

Re: PyQt5 fails to load Could not load the Qt platform plugin "xcb"

Lone_Wolf wrote:
WARNING: QLibraryPrivate::loadPlugin failed on "/home/juanma/Projects/ChemCAD/ChemCAD/venv/lib/python3.7/site-packages/PyQt5/Qt/plugins/platforms/libqxcb.so" : 
"Cannot load library /home/juanma/Projects/ChemCAD/ChemCAD/venv/lib/python3.7/site-packages/PyQt5/Qt/plugins/platforms/libqxcb.so: (/lib/libQt5XcbQpa.so.5: 
symbol _ZTI23QPlatformVulkanInstance version Qt_5_PRIVATE_API not defined in file libQt5Gui.so.5 with link time reference)"
WARNING: Could not load the Qt platform plugin "xcb" in "" even though it was found.

The qt5_private_api part suggests the application expects an older QT5 version , see https://wiki.archlinux.org/index.php/Qt … Qt5_update

Often this can by solved by setting QT_QPA_PLATFORMTHEME explicitly.

Thanks for your answer. I installed all the libraries using a requirements.txt file in the git repo. I installed them all using pip and virtualenv.

In the case of PyQt5 it says it needs PyQt5==5.9.2, which I did install, but it produced the same error. Otherwise using the last PyQt5 in pip (5.12) also produces the same error.

How can I check QT_QPA_PLATFORMTHEME explicitly? I have checked your link to the arch wiki, but I am a bit lost.

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#4 2019-06-12 11:05:23

Lone_Wolf
Member
From: Netherlands, Europe
Registered: 2005-10-04
Posts: 7,050

Re: PyQt5 fails to load Could not load the Qt platform plugin "xcb"

It may be that your python virtenv doesn't use the value for QT_QPA_PLATFORMTHEME that's set in your normal environment

run

$ echo $QT_QPA_PLATFORMTHEME

to see what it is set to, then adjust the virtenv to set QT_QPA_PLATFORMTHEME to the same value.
Test if that solves the issue.


Multi-init booting with apg Openrc and systemd coexisting
Automounting : not needed, i prefer pmount
Aur helpers : makepkg + my own local repo === rarely need them

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#5 2019-06-12 12:39:32

joanmanel
Member
Registered: 2012-11-06
Posts: 141

Re: PyQt5 fails to load Could not load the Qt platform plugin "xcb"

Lone_Wolf wrote:

It may be that your python virtenv doesn't use the value for QT_QPA_PLATFORMTHEME that's set in your normal environment

run

$ echo $QT_QPA_PLATFORMTHEME

to see what it is set to, then adjust the virtenv to set QT_QPA_PLATFORMTHEME to the same value.
Test if that solves the issue.


Both in my virtualenv or my normal environment, this outputs nothing

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#6 2019-06-13 08:04:21

Lone_Wolf
Member
From: Netherlands, Europe
Registered: 2005-10-04
Posts: 7,050

Re: PyQt5 fails to load Could not load the Qt platform plugin "xcb"

That suggests your WM/DE are not Qt-based. What are you using ?


Multi-init booting with apg Openrc and systemd coexisting
Automounting : not needed, i prefer pmount
Aur helpers : makepkg + my own local repo === rarely need them

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#7 2019-06-13 09:59:13

joanmanel
Member
Registered: 2012-11-06
Posts: 141

Re: PyQt5 fails to load Could not load the Qt platform plugin "xcb"

Lone_Wolf wrote:

That suggests your WM/DE are not Qt-based. What are you using ?

I finally fixed the problem by telling virtualenv to use my system packages when possible. It seems there was some mistake between the pip pyqt5 and my WM/DE qt5 installation.

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