Application failed to start because it could not find or load the Qt platform plugin "linuxfb"

Kevin.Wu

Hi Guys.
I cross compiled the Qt5.5.1 source code on a Ubuntu machine, and run the executable file on a embedded ARM. All the .so files I need is accessed using NFS. I wrote a simple demo to check if the work is right , but I just got the error:
Application failed to start because it could not find or load the Qt platform plugin "linuxfb" !

I checked the environment variables I may need to change :
export QT_QPA_PLATFORM=linuxfb:fb=/dev/fb0
export QT_DEBUG_PLUGINS=1
export QTDIR=my NFS path/Qt5.5.1
export QT_QPA_PLATFORM_PLUGIN_PATH=$QTDIR/plugins/platforms
export LD_LIBRARY_PATH=$QTDIR/lib:$LD_LIBRARY_PATH
export QT_PLUGIN_PATH=$QTDIR/plugins/platforms/

The log when I run the demo :

QFactoryLoader::QFactoryLoader() checking directory path "/opt/ipnc/4keptz_project/4keptz_project.si4project/Qt/plugins/platforms" ...
QFactoryLoader::QFactoryLoader() looking at "/opt/ipnc/4keptz_project/4keptz_project.si4project/Qt/plugins/platforms/libqlinuxfb.so"
Found metadata in lib /opt/ipnc/4keptz_project/4keptz_project.si4project/Qt/plugins/platforms/libqlinuxfb.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "linuxfb"
        ]
    },
    "className": "QLinuxFbIntegrationPlugin",
    "debug": false,
    "version": 328961
}


Got keys from plugin meta data ("linuxfb")
QFactoryLoader::QFactoryLoader() looking at "/opt/ipnc/4keptz_project/4keptz_project.si4project/Qt/plugins/platforms/libqminimal.so"
Found metadata in lib /opt/ipnc/4keptz_project/4keptz_project.si4project/Qt/plugins/platforms/libqminimal.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "minimal"
        ]
    },
    "className": "QMinimalIntegrationPlugin",
    "debug": false,
    "version": 328961
}


Got keys from plugin meta data ("minimal")
QFactoryLoader::QFactoryLoader() looking at "/opt/ipnc/4keptz_project/4keptz_project.si4project/Qt/plugins/platforms/libqoffscreen.so"
Found metadata in lib /opt/ipnc/4keptz_project/4keptz_project.si4project/Qt/plugins/platforms/libqoffscreen.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "offscreen"
        ]
    },
    "className": "QOffscreenIntegrationPlugin",
    "debug": false,
    "version": 328961
}


Got keys from plugin meta data ("offscreen")
QFactoryLoader::QFactoryLoader() checking directory path "/opt/ipnc/4keptz_project/4keptz_project.si4project/mg-samples-3.0.12/src/qt/platforms" ...
QFactoryLoader::QFactoryLoader() checking directory path "/opt/ipnc/4keptz_project/4keptz_project.si4project/Qt/plugins/platforms/platforms" ...
This application failed to start because it could not find or load the Qt platform plugin "linuxfd".

Available platform plugins are: linuxfb (from /opt/ipnc/4keptz_project/4keptz_project.si4project/Qt/plugins/platforms), minimal (from /opt/ipnc/4keptz_project/4keptz_project.si4project/Qt/plugins/platforms), offscreen (from /opt/ipnc/4keptz_project/4keptz_project.si4project/Qt/plugins/platforms).

Reinstalling the application may fix this problem.
Aborted

I think I've placed the .so libs at the right place. But I don't know why I get this ? How can I fixed it ?
Thanks.

hskoglund

Hi, it says "linuxfd", if you started your app using the -platform switch, maybe there's a misspelling, say;
"yourapp -platform linuxfd" instead of "yourapp -platform linuxfb"

Kevin.Wu

Sorry for misspelling.. It's the same error when I corrected it..But this time the log says:

QFactoryLoader::QFactoryLoader() checking directory path "/opt/ipnc/4keptz_project/4keptz_project.si4project/Qt/plugins/platforms" ...
QFactoryLoader::QFactoryLoader() looking at "/opt/ipnc/4keptz_project/4keptz_project.si4project/Qt/plugins/platforms/libqlinuxfb.so"
Found metadata in lib /opt/ipnc/4keptz_project/4keptz_project.si4project/Qt/plugins/platforms/libqlinuxfb.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "linuxfb"
        ]
    },
    "className": "QLinuxFbIntegrationPlugin",
    "debug": false,
    "version": 328961
}


Got keys from plugin meta data ("linuxfb")
QFactoryLoader::QFactoryLoader() looking at "/opt/ipnc/4keptz_project/4keptz_project.si4project/Qt/plugins/platforms/libqminimal.so"
Found metadata in lib /opt/ipnc/4keptz_project/4keptz_project.si4project/Qt/plugins/platforms/libqminimal.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "minimal"
        ]
    },
    "className": "QMinimalIntegrationPlugin",
    "debug": false,
    "version": 328961
}


Got keys from plugin meta data ("minimal")
QFactoryLoader::QFactoryLoader() looking at "/opt/ipnc/4keptz_project/4keptz_project.si4project/Qt/plugins/platforms/libqoffscreen.so"
Found metadata in lib /opt/ipnc/4keptz_project/4keptz_project.si4project/Qt/plugins/platforms/libqoffscreen.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "offscreen"
        ]
    },
    "className": "QOffscreenIntegrationPlugin",
    "debug": false,
    "version": 328961
}


Got keys from plugin meta data ("offscreen")
loaded library "/opt/ipnc/4keptz_project/4keptz_project.si4project/Qt/plugins/platforms/libqlinuxfb.so"
QLibraryPrivate::loadPlugin failed on "/opt/ipnc/4keptz_project/4keptz_project.si4project/Qt/plugins/platforms/libqlinuxfb.so" : "Cannot load library /opt/ipnc/4keptz_project/4keptz_project.si4project/Qt/plugins/platforms/libqlinuxfb.so: (**File not found**)"
QFactoryLoader::QFactoryLoader() checking directory path "/opt/ipnc/4keptz_project/4keptz_project.si4project/mg-samples-3.0.12/src/qt/platforms" ...
QFactoryLoader::QFactoryLoader() checking directory path "/opt/ipnc/4keptz_project/4keptz_project.si4project/Qt/plugins/platforms/platforms" ...
This application failed to start because it could not find or load the Qt platform plugin "linuxfb".

libqlinuxfb.so (FIle not found), but I got these libs at the env variable.
ls /opt/ipnc/4keptz_project/4keptz_project.si4project/Qt/plugins/platforms
libqlinuxfb.so libqminimal.so libqoffscreen.so
I don't know what happened..

SGaist

Hi,

Might be a silly question but did you install your cross-compiled Qt on your device ?

Kevin.Wu

@SGaist
I installed my .so libs and app on the Ubuntu. And I run and loaded the libs using NFS.
I found the function "load_sys" in qlibrary_unix.cpp:
pHnd = dlopen(QFile::encodeName(attempt), dlFlags);
always return NULL, the error is : File not Found...But the .so file is just here.

Kevin.Wu

I ‘ve fixed this error’. I add a third party .so in libqlinux.so, but I forgot to set the LD_LIBRARY_PATH to include that .so file. It's really a silly question..sry .

Pablo J. Rogina

@Kevin.Wu glad you figured out the fix. If your issue is solved please don't forget to mark your post as such. Thanks