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

hskoglund

In the long run the best is to do an apt remove for the apt installed Qt and just stick with Qt’s online installer (because it gives you fresher versiobns).

But you can also try to harmonize them, open a Terminal and type qtdiag (it should pick up the apt installed Qt)
Ser what version is says, then use the MaintenanceTool to downgrade to that version.

singhravi

@hskoglund Thanks for the suggestion!
Actually I did not installed the Qt using apt but all the other dependecies such as qtchooser, etc.
Maybe that is why when i ran qtdiag, it gave the following output, qtdiag: could not find a Qt installation of ''?
Please suggest.

hskoglund

Hmm, so apt gave you a piecemeal version of Qt, however enough stuff to error out AppImage.

That older/faulty libQt5XcbQpa.so.5 should be in your /usr/lib/x86_64-linux-gnu anyways, try this in Terminal:

strings /usr/lib/x86_64-linux-gnu/libQt5XcbQpa.so.5 | grep Qt | more

In that list should be some version markers, like Qt_5_PRIVATE_API, Qt_5 and Qt_5.9 or something similar...

Edit: just realized, there's an easier way to establish the version of that apt-flavored partial Qt installation: just list libQt5XcbQpa in Terminal, like this:

ls -l /usr/lib/x86_64-linux-gnu/libQt5Xcb*

this should show what version apt gave you...

singhravi

@hskoglund
Yes, libQt5XcbQpa.so.5 has Qt_5_PRIVATE_API, Qt_5 and Qt_5.9 in it. Please find the whole output below.

_ZN14QXcbConnection19getQtSelectionOwnerEv
_ZN9QtPrivate20QStringList_containsEPK11QStringListRK7QStringN2Qt15CaseSensitivityE
_ZN7QObject10startTimerEiN2Qt9TimerTypeE
_ZN7QObject7connectEPKS_PKcS1_S3_N2Qt14ConnectionTypeE
_ZN11QMetaObject12invokeMethodEP7QObjectPKcN2Qt14ConnectionTypeE22QGenericReturnArgument16QGenericArgumentS7_S7_S7_S7_S7_S7_S7_S7_S7_
_ZN10QByteArrayC1EiN2Qt14InitializationE
_ZN16QCoreApplication13testAttributeEN2Qt20ApplicationAttributeE
_ZNK7QString11lastIndexOfE5QChariN2Qt15CaseSensitivityE
_ZN16QCoreApplication12setAttributeEN2Qt20ApplicationAttributeEb
_ZN7QStringC1EiN2Qt14InitializationE
_ZNK20QPlatformIntegration18defaultWindowStateE6QFlagsIN2Qt10WindowTypeEE
_ZNK11QMetaMethod6invokeEP7QObjectN2Qt14ConnectionTypeE22QGenericReturnArgument16QGenericArgumentS5_S5_S5_S5_S5_S5_S5_S5_S5_
_ZN9QKeyEventC1EN6QEvent4TypeEi6QFlagsIN2Qt16KeyboardModifierEEjjjRK7QStringbt
_ZN22QWindowSystemInterface22handleContextMenuEventEP7QWindowbRK6QPointS4_6QFlagsIN2Qt16KeyboardModifierEE
_ZN22QWindowSystemInterface22handleExtendedKeyEventEP7QWindowmN6QEvent4TypeEi6QFlagsIN2Qt16KeyboardModifierEEjjjRK7QStringbtb
_ZNK7QString10startsWithE13QLatin1StringN2Qt15CaseSensitivityE
_ZNK7QString7indexOfE13QLatin1StringiN2Qt15CaseSensitivityE
_ZNK7QString8splitRefE5QCharNS_13SplitBehaviorEN2Qt15CaseSensitivityE
_ZN10QBasicDrag12updateCursorEN2Qt10DropActionE
_ZN15QtSharedPointer20ExternalRefCountData9getAndRefEPK7QObject
_ZN22QWindowSystemInterface10handleDragEP7QWindowPK9QMimeDataRK6QPoint6QFlagsIN2Qt10DropActionEE
_ZNK23QPlatformDragQtResponse10answerRectEv
_ZNK23QPlatformDropQtResponse10isAcceptedEv
_ZNK23QPlatformDropQtResponse14acceptedActionEv
_ZN22QWindowSystemInterface10handleDropEP7QWindowPK9QMimeDataRK6QPoint6QFlagsIN2Qt10DropActionEE
_ZNK13QPlatformDrag13defaultActionE6QFlagsIN2Qt10DropActionEES0_INS1_16KeyboardModifierEE
_ZN22QWindowSystemInterface29handleScreenOrientationChangeEP7QScreenN2Qt17ScreenOrientationE
_ZN7QObject18staticQtMetaObjectE
_ZN15QPlatformScreen24setOrientationUpdateMaskE6QFlagsIN2Qt17ScreenOrientationEE
_ZN22QWindowSystemInterface21handleWindowActivatedINS_15DefaultDeliveryEEEvP7QWindowN2Qt11FocusReasonE
_ZN10QXcbWindow19setMotifWindowFlagsE6QFlagsIN2Qt10WindowTypeEE
_ZN10QXcbWindow16handleMouseEventEjRK6QPointS2_6QFlagsIN2Qt16KeyboardModifierEENS4_16MouseEventSourceE
_ZN22QWindowSystemInterface16handleMouseEventINS_15DefaultDeliveryEEEvP7QWindowmRK7QPointFS6_6QFlagsIN2Qt11MouseButtonEES7_INS8_16KeyboardModifierEENS8_16MouseEventSourceE
_ZN10QXcbWindow24handleButtonReleaseEventEiiiii6QFlagsIN2Qt16KeyboardModifierEEjNS1_16MouseEventSourceE
_ZN10QXcbWindow23handleMotionNotifyEventEiiii6QFlagsIN2Qt16KeyboardModifierEEjNS1_16MouseEventSourceE
_ZN10QXcbWindow22handleButtonPressEventEiiiii6QFlagsIN2Qt16KeyboardModifierEEjNS1_16MouseEventSourceE
_ZN22QWindowSystemInterface16handleWheelEventEP7QWindowmRK7QPointFS4_iN2Qt11OrientationE6QFlagsINS5_16KeyboardModifierEE
_ZN10QXcbWindow18handleXIMouseEventEP14xcb_ge_event_tN2Qt16MouseEventSourceE
_ZN14QXcbConnection17xiToQtMouseButtonEj
_ZN10QXcbWindow24setNetWmStateWindowFlagsE6QFlagsIN2Qt10WindowTypeEE
_ZN10QXcbWindow14setWindowStateEN2Qt11WindowStateE
_ZThn16_N10QXcbWindow14setWindowStateEN2Qt11WindowStateE
_ZN10QXcbWindow19doStartSystemResizeERK6QPointN2Qt6CornerE
_ZN10QXcbWindow17startSystemResizeERK6QPointN2Qt6CornerE
_ZN14QXcbConnection30startSystemResizeForTouchBeginEjRK6QPointN2Qt6CornerE
_ZThn16_N10QXcbWindow17startSystemResizeERK6QPointN2Qt6CornerE
_ZN10QXcbWindow15setWmWindowTypeE6QFlagsIN19QXcbWindowFunctions12WmWindowTypeEES0_IN2Qt10WindowTypeEE
_ZN22QWindowSystemInterface24handleWindowStateChangedINS_15DefaultDeliveryEEEvP7QWindowN2Qt11WindowStateEi
_ZN10QXcbWindow14setWindowFlagsE6QFlagsIN2Qt10WindowTypeEE
_ZThn16_N10QXcbWindow14setWindowFlagsE6QFlagsIN2Qt10WindowTypeEE
_ZN6QImage23convertToFormat_inplaceENS_6FormatE6QFlagsIN2Qt19ImageConversionFlagEE
_ZNK6QImage22convertToFormat_helperENS_6FormatE6QFlagsIN2Qt19ImageConversionFlagEE
_ZN15QPlatformWindow30handleContentOrientationChangeEN2Qt17ScreenOrientationE
_ZN6QColorC1EN2Qt11GlobalColorE
_ZN22QGuiApplicationPrivate15getPixmapCursorEN2Qt11CursorShapeE
_ZNK6QImage15createAlphaMaskE6QFlagsIN2Qt19ImageConversionFlagEE
_ZN7QPixmap16fromImageInPlaceER6QImage6QFlagsIN2Qt19ImageConversionFlagEE
_ZN22QWindowSystemInterface16handleWheelEventEP7QWindowmRK7QPointFS4_6QPointS5_6QFlagsIN2Qt16KeyboardModifierEENS7_11ScrollPhaseENS7_16MouseEventSourceEb
_ZN22QWindowSystemInterface17handleTabletEventEP7QWindowmRK7QPointFS4_ii6QFlagsIN2Qt11MouseButtonEEdiiddixS5_INS6_16KeyboardModifierEE
_ZN16QLoggingCategory10setEnabledE9QtMsgTypeb
_ZN22QWindowSystemInterface16handleTouchEventINS_15DefaultDeliveryEEEvP7QWindowmP12QTouchDeviceRK5QListINS_10TouchPointEE6QFlagsIN2Qt16KeyboardModifierEE
_ZNK7QString7compareERKS_N2Qt15CaseSensitivityE
_ZN14QFactoryLoaderC1EPKcRK7QStringN2Qt15CaseSensitivityE
_ZN9QtPrivate16QStringList_joinEPK11QStringListPK5QChari
_ZN6QBrushC1EN2Qt11GlobalColorENS0_10BrushStyleE
_ZN6QBrushC1ERK6QColorN2Qt10BrushStyleE
_ZN9QMetaType25registerConverterFunctionEPKN9QtPrivate25AbstractConverterFunctionEii
_ZN9QtPrivate28QStringList_removeDuplicatesEP11QStringList
_ZNK7QString5splitE5QCharNS_13SplitBehaviorEN2Qt15CaseSensitivityE
_ZN7QObject11connectImplEPKS_PPvS1_S3_PN9QtPrivate15QSlotObjectBaseEN2Qt14ConnectionTypeEPKiPK11QMetaObject
_ZNK7QString8endsWithE13QLatin1StringN2Qt15CaseSensitivityE
_ZN6QImage4fillEN2Qt11GlobalColorE
_ZNK7QString7indexOfE5QChariN2Qt15CaseSensitivityE
_ZN20QEventDispatcherGlib13registerTimerEiiN2Qt9TimerTypeEP7QObject
_ZN20QEventDispatcherUNIX13registerTimerEiiN2Qt9TimerTypeEP7QObject
_ZNK6QImage11transformedERK10QTransformN2Qt18TransformationModeE
libQt5Gui.so.5
libQt5DBus.so.5
libQt5Core.so.5
libQt5XcbQpa.so.5
Qt_5_PRIVATE_API
Qt_5
Qt_5.9
Qt: XKEYBOARD extension not present on the X server.
Qt: Failed to initialize XKB extension
Qt: Unsupported XKB version (We want %d %d, but X server has %d %d)
Qt: failed to select notify events from xcb-xkb
Qt: Couldn't interpret the _XKB_RULES_NAMES property
Qt: Failed to compile US keymap, shortcut handling with non-Latin keyboard layouts may not be fully functional!
Qt: failed to retrieve the virtual modifier names from XKB
Qt: failed to retrieve the virtual modifier map from XKB
Qt: failed to get modifier mapping
Qt: failed to retrieve the keyboard mapping from XKB
Qt: Failed to create XKB context!
Qt: Could not determine keyboard configuration data from X server, will use hard-coded keymap configuration.
Qt: Failed to compile a keymap!
Qt: Failed to create xkb state!
Qt: couldn't get core keyboard device info
XInput version %d.%d is available and Qt supports 2.2 or greater
Qt: Session management error: %s
org.qt-project.Qt.QPA.Xcb.QXcbGlIntegrationFactoryInterface.5.5
QtMetaTypePrivate::QSequentialIterableImpl
      <annotation value="QDBusMenuLayoutItem" name="org.qtproject.QtDBus.QtTypeName.Out1"/>
      <annotation value="QList&lt;int&gt;" name="org.qtproject.QtDBus.QtTypeName.In0"/>
      <annotation value="QDBusMenuItemList" name="org.qtproject.QtDBus.QtTypeName.Out0"/>
      <annotation value="QList&lt;QDBusMenuEvent&gt;" name="org.qtproject.QtDBus.QtTypeName.In0"/>
      <annotation value="QList&lt;int&gt;" name="org.qtproject.QtDBus.QtTypeName.Out0"/>
      <annotation value="QList&lt;int&gt;" name="org.qtproject.QtDBus.QtTypeName.In0"/>
      <annotation value="QList&lt;int&gt;" name="org.qtproject.QtDBus.QtTypeName.Out0"/>
      <annotation value="QList&lt;int&gt;" name="org.qtproject.QtDBus.QtTypeName.Out1"/>
      <annotation value="QDBusMenuItemList" name="org.qtproject.QtDBus.QtTypeName.In0"/>
      <annotation value="QDBusMenuItemKeysList" name="org.qtproject.QtDBus.QtTypeName.In1"/>
      <annotation value="QXdgDBusImageVector" name="org.qtproject.QtDBus.QtTypeName"/>
      <annotation value="QXdgDBusImageVector" name="org.qtproject.QtDBus.QtTypeName"/>
      <annotation value="QXdgDBusImageVector" name="org.qtproject.QtDBus.QtTypeName"/>
      <annotation value="QXdgDBusToolTipStruct" name="org.qtproject.QtDBus.QtTypeName"/>
Note that Qt no longer ships fonts. Deploy some (from http://dejavu-fonts.org for example) or switch to fontconfig.
QtMetaTypePrivate::QPairVariantInterfaceImpl
QtMetaTypePrivate::QAssociativeIterableImpl
WARNING Qt AtSpiAdaptor: Could not find accessible on path: 
WARNING Qt AtSpiAdaptor: Could not find application interface for: 
WARNING Qt AtSpiAdaptor: Could not find table interface for: 
WARNING Qt AtSpiAdaptor: Accessible invalid: 
      <annotation value="QSpiAttributeSet" name="org.qtproject.QtDBus.QtTypeName.Out0"/>
      <annotation value="QSpiAttributeSet" name="org.qtproject.QtDBus.QtTypeName.Out0"/>
      <annotation value="QSpiRangeList" name="org.qtproject.QtDBus.QtTypeName.Out0"/>
      <annotation value="QSpiAttributeSet" name="org.qtproject.QtDBus.QtTypeName.Out0"/>
      <annotation value="QSpiAttributeSet" name="org.qtproject.QtDBus.QtTypeName.Out0"/>
      <annotation value="QSpiObjectReference" name="org.qtproject.QtDBus.QtTypeName"/>
      <annotation value="QSpiObjectReference" name="org.qtproject.QtDBus.QtTypeName"/>
      <annotation value="QSpiObjectReference" name="org.qtproject.QtDBus.QtTypeName.Out0"/>
      <annotation value="QSpiObjectReference" name="org.qtproject.QtDBus.QtTypeName.Out0"/>
      <annotation value="QSpiObjectReference" name="org.qtproject.QtDBus.QtTypeName.Out0"/>
      <annotation value="QSpiIntList" name="org.qtproject.QtDBus.QtTypeName.Out0"/>
      <annotation value="QSpiIntList" name="org.qtproject.QtDBus.QtTypeName.Out0"/>
      <annotation value="QSpiObjectReference" name="org.qtproject.QtDBus.QtTypeName.Out0"/>
      <annotation value="QSpiRect" name="org.qtproject.QtDBus.QtTypeName.Out0"/>
      <annotation value="QSpiActionArray" name="org.qtproject.QtDBus.QtTypeName.Out0"/>
      <annotation value="QSpiObjectReference" name="org.qtproject.QtDBus.QtTypeName"/>
      <annotation value="QSpiObjectReference" name="org.qtproject.QtDBus.QtTypeName.Out0"/>
      <annotation value="QSpiObjectReferenceArray" name="org.qtproject.QtDBus.QtTypeName.Out0"/>
      <annotation value="QSpiRelationArray" name="org.qtproject.QtDBus.QtTypeName.Out0"/>
      <annotation value="QSpiUIntList" name="org.qtproject.QtDBus.QtTypeName.Out0"/>
      <annotation value="QSpiAttributeSet" name="org.qtproject.QtDBus.QtTypeName.Out0"/>
      <annotation value="QSpiObjectReference" name="org.qtproject.QtDBus.QtTypeName.Out0"/>
      <annotation value="QSpiAccessibleCacheArray" name="org.qtproject.QtDBus.QtTypeName.Out0"/>
      <annotation value="QSpiAccessibleCacheItem" name="org.qtproject.QtDBus.QtTypeName.Out0"/>
      <annotation value="QSpiObjectReference" name="org.qtproject.QtDBus.QtTypeName.Out0"/>
      <annotation value="QSpiDeviceEvent" name="org.qtproject.QtDBus.QtTypeName.In0"/>
      <annotation value="QSpiDeviceEvent" name="org.qtproject.QtDBus.QtTypeName.In0"/>

Does that mean that this library is for Qt 5.9? And is not compatible with Qt 5.12.9 that we have installed with Qt installer?

We're getting the similar results for the ls command,

-rw-r--r-- 1 root root    1602 Feb  7  2020 /usr/lib/x86_64-linux-gnu/libQt5XcbQpa.prl
lrwxrwxrwx 1 root root      21 Feb  7  2020 /usr/lib/x86_64-linux-gnu/libQt5XcbQpa.so -> libQt5XcbQpa.so.5.9.5
lrwxrwxrwx 1 root root      21 Feb  7  2020 /usr/lib/x86_64-linux-gnu/libQt5XcbQpa.so.5 -> libQt5XcbQpa.so.5.9.5
lrwxrwxrwx 1 root root      21 Feb  7  2020 /usr/lib/x86_64-linux-gnu/libQt5XcbQpa.so.5.9 -> libQt5XcbQpa.so.5.9.5
-rw-r--r-- 1 root root 1070840 Feb  7  2020 /usr/lib/x86_64-linux-gnu/libQt5XcbQpa.so.5.9.5

hskoglund

Indeed, the apt version of Qt you've got is 5.9.5. which does not play well with 5.12.9 :-(

Easiest short-term solution to get AppImage working is to try downgrade your 5.12.9 to 5.9.5 (with a bit of luck any 5.9.x version will do, but see if you can find 5.9.5 first).

(Long-term: try purging all apt-flavored Qt stuff from your Ubuntu system and rely solely on Qt's online installer.)

singhravi

@hskoglund Thanks for the confirmation!
Actually as per the application doc, its required to be 5.12 or greater,
For Desktop : you will need Qt5 (5.12 or newer). C++11 support is required!

I've uninstalled qt5-doc and other dependent packages installed via apt and built it again but xcb error is still there.
I'm checking if there is anything else remained to be removed.
Will update.

hskoglund

@singhravi To get rid of that faulty libQt5XcbQpa.so.5, try:

sudo apt remove libqt5gui5

(note: just guessing..)

singhravi

@hskoglund Yeah this should remove it. But wouldn't this library be needed by the Qt installed by online installer?
Let me run the build after removing this meanwhile.

singhravi

@hskoglund Actually other programs are depending on this qt library installed. Like VLC player, screen recorder and other Qt based apps.
So doing sudo apt remove libqt5gui5 would also remove those apps.

hskoglund

If those other programs are installed using apt, then apt should warn you if you issue a sudo apt remove libqt5gui5, then other programs are dependent on it (I think so). But I suggest yoy go for it and try the AppImage. Later, if the VLC player malfunctions, you can always do:
sudo apt install libqt5gui5

Also, about the Qt version installed by the online installer: it resides 100% in your $HOME directory, it does not touch anything in /usr/lib/x86_64-linux-gnu, nor does it need any Qt files to be installed in /usr/lib/x86_64-linux-gnu.

Only disadvantage is that, since apt is unaware of it, you have to keep it updated yourself (but Qt Creator has a nice plugin that periodically checks that for you).

singhravi

@hskoglund Yup, when ahead with this as the primary focus right now is to get this going.
And then i ran the command to create the build as well.
But it failed as qmake was not able to find Qt.

[qt/stdout] Found Qt modules: concurrent core dbus gui network qml quick quickcontrols2 quicktemplates2 svg texttospeech widgets 
[qt/stdout] Extra Qt modules:  
[qt/stdout] Using qmake: /usr/bin/qmake 
[qt/stdout] ERROR: Call to qmake failed: qmake: could not find a Qt installation of ''
[qt/stdout]  
[qt/stdout] ERROR: Failed to query Qt paths using qmake -query

Should i set some environment variable or create some softlinks for installed Qt to be used?
Something of that sort should fixed this i think.

hskoglund

Hmm, if that /usr/bin/qmake is still around, you should get rid of it (I think it's qtchooser):

sudo apt remove qtchooser

Then to point the linphone-desktop package to where your 5.12.9 is, on their github page it says, set these exports:
Qt5_DIR="~/Qt/5.12.9/gcc_64/lib/cmake"
PATH="~/Qt/5.12.9/gcc_64/bin/:$PATH"

singhravi

@hskoglund
The env variables, Qt5_DIR and PATH are set with what you suggested.
I think qmake is required that is why i must have installed it.
I've ran the build again. Lets see.

hskoglund

BTW, found another option: if you can upgrade your Ubuntu 18.04 to 20.04 then you're in luck: the Qt version installed by apt on Ubuntu 20.04 is 5.12.8 :-)

hskoglund

@singhravi Your Qt 5.12.9 has the qmake program in ~/Qt/5.12.9/gcc_64/bin/ so that PATH export setting should point the script to the correct qmake.

singhravi

@hskoglund I believe we've found the solution to this.
The problem was ~ (tlide) was not working with .zshrc config.
Hence qmake and other binary were not being found.
I've changed it to the absolute path now.
Running the build again. Lets see :)

singhravi

It Worked! :facepalm: :D
Thanks a lot @hskoglund for helping me troubleshoot this! You're great.
So the problem was a ~ from the beginning. This was too silly.
Build is sucsessful and Package is running fine now.

hskoglund

Hah, so it was a ~ that sent you on a wild goose chase!
(tildes can be a PITA, I remember tripping on them when trying to ssh into Ubuntu from Windows)
Anways, glad to hear its working now :-)

Jalpesh

@hskoglund thank Man!

sudo apt remove qtchooser
sudo apt install libqt5gui5

boom.... its work

chEguy

Guys I still am getting this error

qt.qpa.xcb: could not connect to display :0
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: eglfs, linuxfb, minimal, minimalegl, offscreen, vnc, xcb.
Aborted

BTW I am using Ubuntu20 on Windows10 with xcvsrv as X server

QtWS: Early Bird Tickets Available!

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