Crash without useful error message when no display available

[nickdesaulniers]

sshing into my headless server with X window forwarding not set up, I get a crash and core dump because there's no display to attach to. This is stupid and PEBKAC, but maybe this case can be cleaned up to not crash.

➜  qdirstat git:(master) ./src/qdirstat
Logging to /tmp/qdirstat-1000.log
[1]    26606 abort (core dumped)  ./src/qdirstat
➜  qdirstat git:(master) cat /tmp/qdirstat-1000.log
2016-12-06 17:53:40.631 [26606] <Info>    Logger.cpp:75 Logger():  -- Log Start --
2016-12-06 17:53:40.638 [26606] <ERROR>   :0 ():  QXcbConnection: Could not connect to display

[nickdesaulniers]

for instance, this can be reproduced when sshing from OSX without the -Y flag. With -Y everything works well.

[nickdesaulniers]

oof it seems to take a while to scan when ssh'ing+X11 forwarding over the local networks. Maybe the scanning is sequentially dependent on updating the display, in order to animate the read job decrements?

[shundhammer]

Qt over ssh is slow since Qt 5.x; this is a known problem: #27

There is a command line option as a workaround: #33

[shundhammer]

Well, it crashes deep within Qt inside the QApplication constructor:

64	int main( int argc, char *argv[] )
65	{
66	    Logger logger( QString( "/tmp/qdirstat-%1.log" ).arg( getuid() ) );
67	
68	    // Set org/app name for QSettings
69	    QCoreApplication::setOrganizationName( "QDirStat" );
70	    QCoreApplication::setApplicationName ( "QDirStat" );
71	
72	    QApplication app( argc, argv);

^^^^^^^^^^^^^^^^^^^^^^ crash ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

73	    QStringList argList = QCoreApplication::arguments();
74	    argList.removeFirst(); // Remove program name
75	
76	    MainWindow mainWin;
77	    mainWin.show();


(gdb) n
Logging to /tmp/qdirstat-17166.log
69	    QCoreApplication::setOrganizationName( "QDirStat" );
(gdb) n
70	    QCoreApplication::setApplicationName ( "QDirStat" );
(gdb) n
72	    QApplication app( argc, argv);
(gdb) n
Program received signal SIGABRT, Aborted.


(gdb) bt
#0  0x00007ffff548a5af in raise () from /lib64/libc.so.6
#1  0x00007ffff548b9aa in abort () from /lib64/libc.so.6
#2  0x00000000004642f5 in qt_logger (msgType=QtFatalMsg, context=..., msg=...) at Logger.cpp:261
#3  0x00007ffff65df0a8 in ?? () from /usr/lib64/libQt5Core.so.5
#4  0x00007ffff65e0c19 in QMessageLogger::fatal(char const*, ...) const () from /usr/lib64/libQt5Core.so.5
#5  0x00007ffff04b772e in QXcbConnection::QXcbConnection(QXcbNativeInterface*, bool, unsigned int, char const*) () from /usr/lib64/libQt5XcbQpa.so.5
#6  0x00007ffff04ba8ee in QXcbIntegration::QXcbIntegration(QStringList const&, int&, char**) ()
   from /usr/lib64/libQt5XcbQpa.so.5
#7  0x00007ffff077a4dd in ?? () from /usr/lib64/qt5/plugins/platforms/libqxcb.so
#8  0x00007ffff6d095ed in QPlatformIntegrationFactory::create(QString const&, QStringList const&, int&, char**, QString const&) () from /usr/lib64/libQt5Gui.so.5
#9  0x00007ffff6d177d2 in QGuiApplicationPrivate::createPlatformIntegration() ()
   from /usr/lib64/libQt5Gui.so.5
#10 0x00007ffff6d1826d in QGuiApplicationPrivate::createEventDispatcher() () from /usr/lib64/libQt5Gui.so.5
#11 0x00007ffff67cf74f in QCoreApplicationPrivate::init() () from /usr/lib64/libQt5Core.so.5
#12 0x00007ffff6d19d8f in QGuiApplicationPrivate::init() () from /usr/lib64/libQt5Gui.so.5
#13 0x00007ffff74c3619 in QApplicationPrivate::init() () from /usr/lib64/libQt5Widgets.so.5
#14 0x000000000041cecd in main (argc=2, argv=0x7fffffffe128) at main.cpp:72

It crashes because Qt itself calls fatal() which prints an error message and then calls abort() which sends itself a SIGABRT.

The logger could duplicate the fatal error message to stderr, but that's about all the app can do. In particular, it cannot simply continue.

[shundhammer]

Now duplicating a fatal message to stderr, and in the particular case of "Could not connect to display" (and only then) simply calling exit(1), not abort() which dumps core:

[shundhammer @ balrog] ~ 10 % ssh morgul
Last login: Wed Dec  7 11:52:30 2016 from 10.160.4.22
Have a lot of fun...
[shundhammer @ morgul] ~ 1 % cd src/misc/qdirstat/src 
[shundhammer @ morgul] ...misc/qdirstat/src 2 % ./qdirstat /tmp
Logging to /tmp/qdirstat-17166.log
FATAL: QXcbConnection: Could not connect to display