Static Qt: This application failed to start because it could not find or load the Qt platform plugin "xcb".

gergap

Hi

I've build static Qt libraries (5.4.1) to minimize dependencies and simplify deploying of Qt applications on Linux. Therefore I used the settings described here: https://doc-snapshots.qt.io/qtifw-master/ifw-getting-started.html#setting-up-qt-installer-framework

Then I'm using a CMake based build procedure which seems to work.
Here is the ldd output of a simple helloworld application:

> ldd helloworld 
    linux-vdso.so.1 (0x00007fff8d9fe000)
    libharfbuzz.so.0 => /usr/lib64/libharfbuzz.so.0 (0x00007ff4a3a6e000)
    libicui18n.so.54 => /usr/lib64/libicui18n.so.54 (0x00007ff4a3621000)
    libicuuc.so.54 => /usr/lib64/libicuuc.so.54 (0x00007ff4a3296000)
    libicudata.so.54 => /usr/lib64/libicudata.so.54 (0x00007ff4a186b000)
    libdl.so.2 => /lib64/libdl.so.2 (0x00007ff4a1667000)
    librt.so.1 => /lib64/librt.so.1 (0x00007ff4a145f000)
    libpthread.so.0 => /lib64/libpthread.so.0 (0x00007ff4a1242000)
    libstdc++.so.6 => /usr/lib/gcc/x86_64-pc-linux-gnu/4.8.3/libstdc++.so.6 (0x00007ff4a0f3e000)
    libm.so.6 => /lib64/libm.so.6 (0x00007ff4a0c3e000)
    libgcc_s.so.1 => /usr/lib/gcc/x86_64-pc-linux-gnu/4.8.3/libgcc_s.so.1 (0x00007ff4a0a28000)
    libc.so.6 => /lib64/libc.so.6 (0x00007ff4a0685000)
    /lib64/ld-linux-x86-64.so.2 (0x00007ff4a3cc6000)
    libglib-2.0.so.0 => /usr/lib64/libglib-2.0.so.0 (0x00007ff4a0352000)
    libfreetype.so.6 => /usr/lib64/libfreetype.so.6 (0x00007ff4a00ab000)
    libgraphite2.so.3 => /usr/lib64/libgraphite2.so.3 (0x00007ff49fe8c000)
    libz.so.1 => /lib64/libz.so.1 (0x00007ff49fc76000)
    libbz2.so.1 => /lib64/libbz2.so.1 (0x00007ff49fa66000)
    libpng16.so.16 => /usr/lib64/libpng16.so.16 (0x00007ff49f831000)

But when starting the application I get this error:
This application failed to start because it could not find or load the Qt platform plugin "xcb".

I was expecting due to the option "-qt-xcb" and static linking I would not need that plugin. Actually there is only a static library Qt/5.4.1-static/plugins/platforms/libqxcb.a

What am I doing wrong here?

Build process output:

[ 66%] Building CXX object CMakeFiles/helloworld.dir/main.cpp.o
/usr/bin/g++   -DQT_CORE_LIB -DQT_GUI_LIB -DQT_NO_DEBUG -DQT_WIDGETS_LIB -fdata-sections -ffunction-sections -Os -DNDEBUG -fPIE -I/home/gergap/work/devel/helloworld/bld -I/home/gergap/work/devel/helloworld -I/home/gergap/Qt/5.4.1-static/include -I/home/gergap/Qt/5.4.1-static/include/QtWidgets -I/home/gergap/Qt/5.4.1-static/include/QtGui -I/home/gergap/Qt/5.4.1-static/include/QtCore -I/home/gergap/Qt/5.4.1-static/mkspecs/linux-g++    -o CMakeFiles/helloworld.dir/main.cpp.o -c /home/gergap/work/devel/helloworld/main.cpp
/usr/bin/cmake -E cmake_progress_report /home/gergap/work/devel/helloworld/bld/CMakeFiles 2
[100%] Building CXX object CMakeFiles/helloworld.dir/helloworld_automoc.cpp.o
/usr/bin/g++   -DQT_CORE_LIB -DQT_GUI_LIB -DQT_NO_DEBUG -DQT_WIDGETS_LIB -fdata-sections -ffunction-sections -Os -DNDEBUG -fPIE -I/home/gergap/work/devel/helloworld/bld -I/home/gergap/work/devel/helloworld -I/home/gergap/Qt/5.4.1-static/include -I/home/gergap/Qt/5.4.1-static/include/QtWidgets -I/home/gergap/Qt/5.4.1-static/include/QtGui -I/home/gergap/Qt/5.4.1-static/include/QtCore -I/home/gergap/Qt/5.4.1-static/mkspecs/linux-g++    -o CMakeFiles/helloworld.dir/helloworld_automoc.cpp.o -c /home/gergap/work/devel/helloworld/bld/helloworld_automoc.cpp
Linking CXX executable helloworld
/usr/bin/cmake -E cmake_link_script CMakeFiles/helloworld.dir/link.txt --verbose=1
/usr/bin/g++    -fdata-sections -ffunction-sections -Os -DNDEBUG    -Wl,--gc-sections CMakeFiles/helloworld.dir/main.cpp.o CMakeFiles/helloworld.dir/helloworld_automoc.cpp.o  -o helloworld -rdynamic /home/gergap/Qt/5.4.1-static/lib/libQt5Widgets.a -lharfbuzz -licui18n -licuuc -licudata -ldl -lrt -lpthread /home/gergap/Qt/5.4.1-static/lib/libQt5Gui.a /home/gergap/Qt/5.4.1-static/lib/libQt5Core.a 
make[2]: Leaving directory '/home/gergap/work/devel/helloworld/bld'
/usr/bin/cmake -E cmake_progress_report /home/gergap/work/devel/helloworld/bld/CMakeFiles  1 2
[100%] Built target helloworld

Rondog

The plugin libraries are loaded by the application at run time. 'xcb' is a platform plugin for GNU/Linux. You may need others depending on your application. I don't think a static version extends to the plugins.

Maybe you are simply missing the plugin directory under the application. You should have a folder called 'platforms' containing 'libqxcb.so' as a minimum.

gergap

Because I built a static Qt it contains a plugins/platforms/libqxcb.a and not an so. That's the reason why I don't understand why it fails with this error.

kkoehne

When compiling a static application, qmake does automatically link in Qt plugins (see e.g. http://doc.qt.io/qt-5/plugins-howto.html#static-plugins). Anyhow, you're using cmake, so you need to find a way to let cmake do the same ....

gergap

Thx for that tip. I tried qmake to get an example which I then can use to do the same with cmake. Unfortunately it also doesn' work with qmake.

TEMPLATE = app
CONFIG = qt static
QT = core gui widgets
QTPLUGIN.platforms = qxcb

SOURCES = main.cpp
# add missing libraries
LIBS += -lharfbuzz -licui18n -licuuc -licudata -ldl -lrt -lpthread

This gives me this warning when running qmake:

Project WARNING: CONFIG-=import_qpa_plugin is deprecated. Use QTPLUGIN.platforms=- instead.

and it does not link qxcb.

Even when I manually link this library libqxcb.a I still get the error at runtime:

This application failed to start because it could not find or load the Qt platform plugin "xcb".

Probably I need also some special compile definitions, but I don' know which.

Is there somewhere an example how to make a simple helloworld example working with static Qt and xcb? Having a working qmake example would be enough.

here is my helloworld main.cpp:

#include <QApplication>
#include <QPushButton>

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    QPushButton test("Hello World");

    test.show();

    return app.exec();
}

gergap

I found the issue with qmake ;-)

CONFIG += qt static

instead of

CONFIG = qt static

d_h_mcinnes

Hi gergap, did you ever figure this out? I have the exact same problem :(