I'm having difficulty running any Qt5 application. These are the 
commands I'm issuing:

     XWin -multiwindow &
     export DISPLAY=:0.0
     xclock &

and I see the clock, so X is up and running. Then:

     /usr/lib/qt5/examples/gui/analogclock/analogclock
     QXcbConnection: XCB error: 145 (Unknown), sequence: 162, resource 
id: 0, major c
     ode: 140 (Unknown), minor code: 20
     Bad system call (core dumped)

and no clock.

I've tried compiling a really trivial Qt5 example (attached):

     g++ -I/usr/include/qt5 -I/usr/include/qt5/QtWidgets 
-I/usr/include/qt5/QtGui \
     -o qt5-demo qt5-demo.cpp -lQt5Widgets -lQt5Core

And then running ./qt5-demo gives:

     QObject::connect: signal not found in QPushButton
     QObject::connect: signal not found in QWidget
     QObject::connect: signal not found in QWidget
     QXcbConnection: XCB error: 145 (Unknown), sequence: 162, resource 
id: 0, major
     code: 140 (Unknown), minor code: 20
     Bad system call (core dumped)

The demo runs fine in Fedora 21. It also runs in Cygwin when compiled 
with Qt4:

     g++ -I/usr/include/qt4 -I/usr/include/qt4/QtGui -o qt5-demo 
qt5-demo.cpp \
     -lQtGui -lQtCore

And now running the (incorrectly-named!) ./qt5-demo launches the 
application.

Please could you advise what I'm doing wrong.

Many thanks in advance,

Dave.