Virtualbox cannot load libqxcb.so ; I know you are tried & have disdain to answer this question again, but its weird.

DC.QT

[Issue]
I had Qt5.7 installed before, it said "Cannot load library libqxcb.so" error.
After that, I installed Qt5.9.5, but the issue still there.
Qt WARNING: QLibraryPrivate::loadPlugin failed on "/home/myID/Qt5/5.9.5/gcc_64/plugins/platforms/libqxcb.so" : "Cannot load library /home/myID/Qt5/5.9.5/gcc_64/plugins/platforms/libqxcb.so: "
Qt FATAL: This application failed to start because it could not find or load the Qt platform plugin "xcb"
in "".
[QT ENV]

Qt5.9.5 is installed in /home/myID/Qt5/5.9.5/gcc_64/
I already set following ENV:

PATH="$HOME/bin:$HOME/.local/bin:$PATH"
QT_HOME=/home/myID/Qt5/5.9.5/gcc_64
QT_PLUGIN_PATH=$QT_HOME/plugins
# QT_QPA_PLATFORM_PLUGIN_PATH=$QT_HOME/plugins/platforms
QT_QPA_PLATFORM_PLUGIN_PATH=$QT_HOME/plugins
LD_LIBRARY_PATH=.:$LD_LIBRARY_PATH:$QT_HOME/lib:$QT_PLUGIN_PATH:$QT_QPA_PLATFORM_PLUGIN_PATH
QML_IMPORT_PATH=$QT_HOME/qml
QML2_IMPORT_PATH=$QT_HOME/qml

/usr/lib/x86_64-linux-gnu/qt-default/qtchooser/default.conf -> ../../../../share/qtchooser/qt5-x86_64-linux-gnu_595.conf
/usr/share/qtchooser/default --> qt5-x86_64-linux-gnu_595.conf
which has the content:

/home/myID/Qt5/5.9.5/gcc_64/bin
/home/myID/Qt5/5.9.5/gcc_64

Already set it as somebody's suggestion.
/usr/bin/platforms -> /home/myID/Qt5/5.9.5/gcc_64/plugins/platforms/
export QT_DEBUG_PLUGINS=1, then has the output:

Qt WARNING: Found metadata in lib /home/myID/Qt5/5.9.5/gcc_64/plugins/platforms/libqeglfs.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "eglfs"
        ]
    },
    "className": "QEglFSIntegrationPlugin",
    "debug": false,
    "version": 329989
}


Qt WARNING: Found metadata in lib /home/myID/Qt5/5.9.5/gcc_64/plugins/platforms/libqlinuxfb.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "linuxfb"
        ]
    },
    "className": "QLinuxFbIntegrationPlugin",
    "debug": false,
    "version": 329989
}


Qt WARNING: Found metadata in lib /home/myID/Qt5/5.9.5/gcc_64/plugins/platforms/libqminimal.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "minimal"
        ]
    },
    "className": "QMinimalIntegrationPlugin",
    "debug": false,
    "version": 329989
}


Qt WARNING: Found metadata in lib /home/myID/Qt5/5.9.5/gcc_64/plugins/platforms/libqminimalegl.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "minimalegl"
        ]
    },
    "className": "QMinimalEglIntegrationPlugin",
    "debug": false,
    "version": 329989
}


Qt WARNING: Found metadata in lib /home/myID/Qt5/5.9.5/gcc_64/plugins/platforms/libqoffscreen.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "offscreen"
        ]
    },
    "className": "QOffscreenIntegrationPlugin",
    "debug": false,
    "version": 329989
}


Qt WARNING: Found metadata in lib /home/myID/Qt5/5.9.5/gcc_64/plugins/platforms/libqvnc.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "vnc"
        ]
    },
    "className": "QVncIntegrationPlugin",
    "debug": false,
    "version": 329989
}


Qt WARNING: Found metadata in lib /home/myID/Qt5/5.9.5/gcc_64/plugins/platforms/libqxcb.so, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "xcb"
        ]
    },
    "className": "QXcbIntegrationPlugin",
    "debug": false,
    "version": 329989
}


Qt WARNING: QLibraryPrivate::loadPlugin failed on "/home/myID/Qt5/5.9.5/gcc_64/plugins/platforms/libqxcb.so" : "Cannot load library /home/myID/Qt5/5.9.5/gcc_64/plugins/platforms/libqxcb.so: "
Qt FATAL: This application failed to start because it could not find or load the Qt platform plugin "xcb"
in "".

Available platform plugins are: eglfs, linuxfb, minimal, minimalegl, offscreen, vnc, xcb.

Reinstalling the application may fix this problem.
Aborted (core dumped)

The metadata be found from the right libraries.
And Im sure the '/home/myID/Qt5/5.9.5/gcc_64/plugins/platforms/libqxcb.so' is be there.
6. ldd outputs:

$ ldd /home/myID/Qt5/5.9.5/gcc_64/plugins/platforms/libqxcb.so
	linux-vdso.so.1 (0x00007fffa19b4000)
	libQt5XcbQpa.so.5 => /home/myID/Qt5/5.9.5/gcc_64/lib/libQt5XcbQpa.so.5 (0x00007f2976100000)
	libgthread-2.0.so.0 => /usr/lib/x86_64-linux-gnu/libgthread-2.0.so.0 (0x00007f2975efe000)
	libglib-2.0.so.0 => /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0 (0x00007f2975be8000)
	libfontconfig.so.1 => /usr/lib/x86_64-linux-gnu/libfontconfig.so.1 (0x00007f29759a3000)
	libfreetype.so.6 => /usr/lib/x86_64-linux-gnu/libfreetype.so.6 (0x00007f29756ef000)
	libQt5Gui.so.5 => /home/myID/Qt5/5.9.5/gcc_64/lib/libQt5Gui.so.5 (0x00007f2974f3e000)
	libQt5DBus.so.5 => /home/myID/Qt5/5.9.5/gcc_64/lib/libQt5DBus.so.5 (0x00007f2974cb5000)
	libQt5Core.so.5 => /home/myID/Qt5/5.9.5/gcc_64/lib/libQt5Core.so.5 (0x00007f2974578000)
	libGL.so.1 => /usr/lib/x86_64-linux-gnu/libGL.so.1 (0x00007f29742ec000)
	libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f29740cd000)
	libX11-xcb.so.1 => /usr/lib/x86_64-linux-gnu/libX11-xcb.so.1 (0x00007f2973ecb000)
	libX11.so.6 => /usr/lib/x86_64-linux-gnu/libX11.so.6 (0x00007f2973b93000)
	libXi.so.6 => /usr/lib/x86_64-linux-gnu/libXi.so.6 (0x00007f2973983000)
	libxcb.so.1 => /usr/lib/x86_64-linux-gnu/libxcb.so.1 (0x00007f297375b000)
	libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f2973557000)
	libstdc++.so.6 => /usr/lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007f29731c9000)
	libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f2972e2b000)
	libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007f2972c13000)
	libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f2972822000)
	libpcre.so.3 => /lib/x86_64-linux-gnu/libpcre.so.3 (0x00007f29725b0000)
	libexpat.so.1 => /lib/x86_64-linux-gnu/libexpat.so.1 (0x00007f297237e000)
	libpng16.so.16 => /usr/lib/x86_64-linux-gnu/libpng16.so.16 (0x00007f297214c000)
	libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007f2971f2f000)
	libdbus-1.so.3 => /lib/x86_64-linux-gnu/libdbus-1.so.3 (0x00007f2971ce2000)
	libicui18n.so.56 => /home/myID/Qt5/5.9.5/gcc_64/lib/libicui18n.so.56 (0x00007f2971849000)
	libicuuc.so.56 => /home/myID/Qt5/5.9.5/gcc_64/lib/libicuuc.so.56 (0x00007f2971491000)
	libicudata.so.56 => /home/myID/Qt5/5.9.5/gcc_64/lib/libicudata.so.56 (0x00007f296faae000)
	/lib64/ld-linux-x86-64.so.2 (0x00007f2976658000)
	libGLX.so.0 => /usr/lib/x86_64-linux-gnu/libGLX.so.0 (0x00007f296f87d000)
	libGLdispatch.so.0 => /usr/lib/x86_64-linux-gnu/libGLdispatch.so.0 (0x00007f296f5c7000)
	libXext.so.6 => /usr/lib/x86_64-linux-gnu/libXext.so.6 (0x00007f296f3b5000)
	libXau.so.6 => /usr/lib/x86_64-linux-gnu/libXau.so.6 (0x00007f296f1b1000)
	libXdmcp.so.6 => /usr/lib/x86_64-linux-gnu/libXdmcp.so.6 (0x00007f296efab000)
	libsystemd.so.0 => /lib/x86_64-linux-gnu/libsystemd.so.0 (0x00007f296ed27000)
	libbsd.so.0 => /lib/x86_64-linux-gnu/libbsd.so.0 (0x00007f296eb12000)
	librt.so.1 => /lib/x86_64-linux-gnu/librt.so.1 (0x00007f296e90a000)
	liblzma.so.5 => /lib/x86_64-linux-gnu/liblzma.so.5 (0x00007f296e6e4000)
	liblz4.so.1 => /usr/lib/x86_64-linux-gnu/liblz4.so.1 (0x00007f296e4c8000)
	libgcrypt.so.20 => /lib/x86_64-linux-gnu/libgcrypt.so.20 (0x00007f296e1ad000)
	libgpg-error.so.0 => /lib/x86_64-linux-gnu/libgpg-error.so.0 (0x00007f296df98000)

It seems all right there.
I have no idea what's wrong with it.
BTW, I had tried to 'apt remove virtualbox' and 'apt install virtualbox' it again, but issue still be there.
Please, pls, help me.....

sierdzio

Which operating system are your running in that virtual machine? Have you tried a clean install of the OS, then clean install of Qt (without setting up any environment vars)? Do you have 3D acceleration enabled for that VM in VirtualBox settings?

Lastly, have you installed the dependencies:

sudo apt build-dep qt5-qmake
# or
sudo apt build-dep qt5-default

DC.QT

@sierdzio said in Virtualbox cannot load libqxcb.so ; I know you are tried & have disdain to answer this question again, but its weird.:

acceleration enabled for that VM in VirtualBo

Thanks for reply.
OS is Ubuntu 18.04 LST.
Sorry, my mistake. I am trying to run 'virtualbox' application on that Ubuntu 18.04 (64bit) platform. Not in virtual machine environment.

sierdzio

@DC.QT said in Virtualbox cannot load libqxcb.so ; I know you are tried & have disdain to answer this question again, but its weird.:

Sorry, my mistake. I am trying to run 'virtualbox' application on that Ubuntu 18.04 (64bit) platform. Not in virtual machine environment.

Then don't use custom Qt installation for that. Just install virtualbox package via apt or GUI package manager and run it. There is no need to install Qt manually for that.