Hi,
When I try to logon KDE 5, I have a black screen and a cursor, I still can launch anything I want using ALT+F2, and I still can have Yakuake with F12, I don't know if it's because of an update,
I tried to logon from SDDM and manually from a TTY terminal, with no difference,
I tried to start manually Plasmashell from a terminal (both "plasmashell" ans "kstart5 plasmashell", but no difference...), and it complained with 2 lines :

Code: Select all

QSocketNotifier: Invalid Socket 8 and type 'Read', disabling...
QSocketNotifier: Invalid socket 9 and type 'Read', disabling...


Here is further information when launched from a debugger :

Code: Select all

(lldb) target create "plasmashell"
Current executable set to 'plasmashell' (x86_64).
(lldb) r
Process 24233 launched: '/usr/bin/plasmashell' (x86_64)
Process 24233 stopped and restarted: thread 1 received signal: SIGCHLD
org.kde.plasmaquick: Applet preload policy set to 1
file:///usr/share/plasma/plasmoids/org.kde.desktopcontainment/contents/ui/main.qml:62:5: Unable to assign [undefined] to int
file:///usr/share/plasma/plasmoids/org.kde.desktopcontainment/contents/ui/main.qml:53:5: Unable to assign [undefined] to int
kf5.kpackage: No metadata file in the package, expected it at: "/home/fran/Images/"
kf5.kpackage: No metadata file in the package, expected it at: "/home/fran/Images/"
kf5.kpackage: No metadata file in the package, expected it at: "/home/fran/Images/"
trying to show an empty dialog
file:///usr/share/plasma/shells/org.kde.plasma.desktop/contents/views/Desktop.qml:146:19: QML Loader: Binding loop detected for property "height"
file:///usr/share/plasma/shells/org.kde.plasma.desktop/contents/views/Desktop.qml:146:19: QML Loader: Binding loop detected for property "height"
Process 24233 stopped and restarted: thread 1 received signal: SIGCHLD
Process 24233 stopped and restarted: thread 1 received signal: SIGCHLD
Connecting to deprecated signal QDBusConnectionInterface::serviceOwnerChanged(QString,QString,QString)
Trying to use rootObject before initialization is completed, whilst using setInitializationDelayed. Forcing completion
Process 24233 stopped
* thread #1, name = 'plasmashell', stop reason = signal SIGSEGV: invalid address (fault address: 0x10)
    frame #0: 0x00007ffff5a74b56 libQt5Core.so.5`___lldb_unnamed_symbol2971$$libQt5Core.so.5 + 118
libQt5Core.so.5`___lldb_unnamed_symbol2971$$libQt5Core.so.5:
->  0x7ffff5a74b56 <+118>: addq   0x10(%rax), %rbp
    0x7ffff5a74b5a <+122>: je     0x7ffff5a74ba2            ; <+194>
    0x7ffff5a74b5c <+124>: movl   0x4(%rax), %eax
    0x7ffff5a74b5f <+127>: testl  %eax, %eax
(lldb) bt
* thread #1, name = 'plasmashell', stop reason = signal SIGSEGV: invalid address (fault address: 0x10)
  * frame #0: 0x00007ffff5a74b56 libQt5Core.so.5`___lldb_unnamed_symbol2971$$libQt5Core.so.5 + 118
    frame #1: 0x00007ffff5a761f6 libQt5Core.so.5`___lldb_unnamed_symbol2980$$libQt5Core.so.5 + 182
    frame #2: 0x00007ffff5a76726 libQt5Core.so.5`___lldb_unnamed_symbol2985$$libQt5Core.so.5 + 38
    frame #3: 0x00007ffff5a1ab41 libQt5Core.so.5`QDateTime::setMSecsSinceEpoch(long long) + 705
    frame #4: 0x00007ffff5a1c9ab libQt5Core.so.5`QDateTime::fromMSecsSinceEpoch(long long, QTimeZone const&) + 43
    frame #5: 0x00007ffff5a1ca1f libQt5Core.so.5`QDateTime::toTimeZone(QTimeZone const&) const + 95
    frame #6: 0x00007fffd80aba10 plasma_engine_time.so`___lldb_unnamed_symbol44$$plasma_engine_time.so + 80
    frame #7: 0x00007fffd80aeba2 plasma_engine_time.so`___lldb_unnamed_symbol45$$plasma_engine_time.so + 946
    frame #8: 0x00007fffd80af05d plasma_engine_time.so`___lldb_unnamed_symbol46$$plasma_engine_time.so + 157
    frame #9: 0x00007fffd80a9d27 plasma_engine_time.so`___lldb_unnamed_symbol22$$plasma_engine_time.so + 39
    frame #10: 0x00007ffff7b0bccb libKF5Plasma.so.5`___lldb_unnamed_symbol323$$libKF5Plasma.so.5 + 139
    frame #11: 0x00007ffff7b0c557 libKF5Plasma.so.5`Plasma::DataEngine::connectSource(QString const&, QObject*, unsigned int, Plasma::Types::IntervalAlignment) const + 55
    frame #12: 0x00007fffddba1ddc libcorebindingsplugin.so`___lldb_unnamed_symbol517$$libcorebindingsplugin.so + 172
    frame #13: 0x00007fffddb86f5b libcorebindingsplugin.so`___lldb_unnamed_symbol87$$libcorebindingsplugin.so + 1435
    frame #14: 0x00007ffff73b7582 libQt5Qml.so.5`___lldb_unnamed_symbol4362$$libQt5Qml.so.5 + 162
    frame #15: 0x00007ffff73b41fb libQt5Qml.so.5`QQmlPropertyPrivate::write(QObject*, QQmlPropertyData const&, QVariant const&, QQmlContextData*, QFlags<QQmlPropertyData::WriteFlag>) + 219
    frame #16: 0x00007ffff7426ca5 libQt5Qml.so.5`QQmlBinding::slowWrite(QQmlPropertyData const&, QQmlPropertyData const&, QV4::Value const&, bool, QFlags<QQmlPropertyData::WriteFlag>) + 2149
    frame #17: 0x00007ffff7427db1 libQt5Qml.so.5`___lldb_unnamed_symbol5155$$libQt5Qml.so.5 + 241
    frame #18: 0x00007ffff74291c8 libQt5Qml.so.5`___lldb_unnamed_symbol5198$$libQt5Qml.so.5 + 184
    frame #19: 0x00007ffff7425a13 libQt5Qml.so.5`QQmlBinding::update(QFlags<QQmlPropertyData::WriteFlag>) + 531
    frame #20: 0x00007ffff7401183 libQt5Qml.so.5`QQmlNotifier::emitNotify(QQmlNotifierEndpoint*, void**) + 579
    frame #21: 0x00007ffff73a4804 libQt5Qml.so.5`QQmlData::signalEmitted(QAbstractDeclarativeData*, QObject*, int, void**) + 500
    frame #22: 0x00007ffff5bb8aaf libQt5Core.so.5`QMetaObject::activate(QObject*, int, int, void**) + 159
    frame #23: 0x00007ffff73a0e16 libQt5Qml.so.5`QQmlVMEMetaObject::writeVarProperty(int, QV4::Value const&) + 614
    frame #24: 0x00007ffff72fac78 libQt5Qml.so.5`QV4::QObjectWrapper::setProperty(QV4::ExecutionEngine*, QObject*, QQmlPropertyData*, QV4::Value const&) + 1992
    frame #25: 0x00007ffff72fb747 libQt5Qml.so.5`QV4::QObjectWrapper::setQmlProperty(QV4::ExecutionEngine*, QQmlContextData*, QObject*, QV4::String*, QV4::QObjectWrapper::RevisionMode, QV4::Value const&) + 295
    frame #26: 0x00007ffff72fb865 libQt5Qml.so.5`QV4::QObjectWrapper::virtualPut(QV4::Managed*, QV4::PropertyKey, QV4::Value const&, QV4::Value*) + 261
    frame #27: 0x00007ffff72bfb6c libQt5Qml.so.5`QV4::Object::virtualResolveLookupSetter(QV4::Object*, QV4::ExecutionEngine*, QV4::Lookup*, QV4::Value const&) + 540
    frame #28: 0x00007ffff7313b64 libQt5Qml.so.5`___lldb_unnamed_symbol2821$$libQt5Qml.so.5 + 5748
    frame #29: 0x00007ffff731861f libQt5Qml.so.5`___lldb_unnamed_symbol2822$$libQt5Qml.so.5 + 575
    frame #30: 0x00007ffff72a6ac1 libQt5Qml.so.5`___lldb_unnamed_symbol2037$$libQt5Qml.so.5 + 401
    frame #31: 0x00007ffff731554a libQt5Qml.so.5`___lldb_unnamed_symbol2821$$libQt5Qml.so.5 + 12378
    frame #32: 0x00007ffff731861f libQt5Qml.so.5`___lldb_unnamed_symbol2822$$libQt5Qml.so.5 + 575
    frame #33: 0x00007ffff72a5f74 libQt5Qml.so.5`QV4::Function::call(QV4::Value const*, QV4::Value const*, int, QV4::ExecutionContext const*) + 372
    frame #34: 0x00007ffff741e988 libQt5Qml.so.5`QQmlJavaScriptExpression::evaluate(QV4::CallData*, bool*) + 408
    frame #35: 0x00007ffff73c2508 libQt5Qml.so.5`QQmlBoundSignalExpression::evaluate(void**) + 776
    frame #36: 0x00007ffff73c36bc libQt5Qml.so.5`___lldb_unnamed_symbol4423$$libQt5Qml.so.5 + 684
    frame #37: 0x00007ffff7401183 libQt5Qml.so.5`QQmlNotifier::emitNotify(QQmlNotifierEndpoint*, void**) + 579
    frame #38: 0x00007ffff73a4804 libQt5Qml.so.5`QQmlData::signalEmitted(QAbstractDeclarativeData*, QObject*, int, void**) + 500
    frame #39: 0x00007ffff5bb8aaf libQt5Core.so.5`QMetaObject::activate(QObject*, int, int, void**) + 159
    frame #40: 0x00007ffff7434559 libQt5Qml.so.5`QQmlObjectCreator::finalize(QQmlInstantiationInterrupt&) + 1577
    frame #41: 0x00007ffff73bdbdb libQt5Qml.so.5`___lldb_unnamed_symbol4401$$libQt5Qml.so.5 + 1691
    frame #42: 0x00007ffff73be2db libQt5Qml.so.5`___lldb_unnamed_symbol4402$$libQt5Qml.so.5 + 75
    frame #43: 0x00007ffff73be33c libQt5Qml.so.5`QQmlIncubator::forceCompletion() + 76
    frame #44: 0x00007ffff7aa741e libKF5Declarative.so.5`KDeclarative::QmlObject::rootObject() const + 254
    frame #45: 0x00007ffff7f473ae libKF5PlasmaQuick.so.5`___lldb_unnamed_symbol65$$libKF5PlasmaQuick.so.5 + 46
    frame #46: 0x00007ffff7f47f7f libKF5PlasmaQuick.so.5`___lldb_unnamed_symbol66$$libKF5PlasmaQuick.so.5 + 1263
    frame #47: 0x00007ffff7427c74 libQt5Qml.so.5`___lldb_unnamed_symbol5154$$libQt5Qml.so.5 + 1076
    frame #48: 0x00007ffff74291c8 libQt5Qml.so.5`___lldb_unnamed_symbol5198$$libQt5Qml.so.5 + 184
    frame #49: 0x00007ffff7425a13 libQt5Qml.so.5`QQmlBinding::update(QFlags<QQmlPropertyData::WriteFlag>) + 531
    frame #50: 0x00007ffff7434044 libQt5Qml.so.5`QQmlObjectCreator::finalize(QQmlInstantiationInterrupt&) + 276
    frame #51: 0x00007ffff73bdbdb libQt5Qml.so.5`___lldb_unnamed_symbol4401$$libQt5Qml.so.5 + 1691
    frame #52: 0x00007ffff73be1c7 libQt5Qml.so.5`QQmlEnginePrivate::incubate(QQmlIncubator&, QQmlContextData*) + 791
    frame #53: 0x00007ffff73baae7 libQt5Qml.so.5`QQmlComponent::create(QQmlIncubator&, QQmlContext*, QQmlContext*) + 391
    frame #54: 0x00007ffff7aa7ad5 libKF5Declarative.so.5`KDeclarative::QmlObject::completeInitialization(QHash<QString, QVariant> const&) + 261
    frame #55: 0x00007ffff7f48653 libKF5PlasmaQuick.so.5`PlasmaQuick::AppletQuickItem::init() + 1251
    frame #56: 0x00007fffecd39791 plasma_appletscript_declarative.so`___lldb_unnamed_symbol157$$plasma_appletscript_declarative.so + 177
    frame #57: 0x00007ffff7f49bc8 libKF5PlasmaQuick.so.5`PlasmaQuick::AppletQuickItem::itemChange(QQuickItem::ItemChange, QQuickItem::ItemChangeData const&) + 56
    frame #58: 0x00007ffff77e5ea4 libQt5Quick.so.5`QQuickItemPrivate::itemChange(QQuickItem::ItemChange, QQuickItem::ItemChangeData const&) + 740
    frame #59: 0x00007ffff77e99fe libQt5Quick.so.5`QQuickItemPrivate::refWindow(QQuickWindow*) + 222
    frame #60: 0x00007ffff77e99bb libQt5Quick.so.5`QQuickItemPrivate::refWindow(QQuickWindow*) + 155
    frame #61: 0x00007ffff77ec576 libQt5Quick.so.5`QQuickItem::setParentItem(QQuickItem*) + 1542
    frame #62: 0x00007ffff7f58c16 libKF5PlasmaQuick.so.5`___lldb_unnamed_symbol202$$libKF5PlasmaQuick.so.5 + 1366
    frame #63: 0x0000555555597819 plasmashell`___lldb_unnamed_symbol493$$plasmashell + 985
    frame #64: 0x00007ffff5bb92cb libQt5Core.so.5`QMetaObject::activate(QObject*, int, int, void**) + 2235
    frame #65: 0x00007ffff5bc5238 libQt5Core.so.5`QTimer::timeout(QTimer::QPrivateSignal) + 56
    frame #66: 0x00007ffff5bb99eb libQt5Core.so.5`QObject::event(QEvent*) + 155
    frame #67: 0x00007ffff6740da4 libQt5Widgets.so.5`QApplicationPrivate::notify_helper(QObject*, QEvent*) + 132
    frame #68: 0x00007ffff67483c1 libQt5Widgets.so.5`QApplication::notify(QObject*, QEvent*) + 529
    frame #69: 0x00007ffff5b8e7f9 libQt5Core.so.5`QCoreApplication::notifyInternal2(QObject*, QEvent*) + 377
    frame #70: 0x00007ffff5be2cc5 libQt5Core.so.5`QTimerInfoList::activateTimers() + 1061
    frame #71: 0x00007ffff5be3552 libQt5Core.so.5`___lldb_unnamed_symbol4689$$libQt5Core.so.5 + 34
    frame #72: 0x00007ffff3eab7bf libglib-2.0.so.0`g_main_context_dispatch + 703
    frame #73: 0x00007ffff3ead739 libglib-2.0.so.0`___lldb_unnamed_symbol349$$libglib-2.0.so.0 + 569
    frame #74: 0x00007ffff3ead77e libglib-2.0.so.0`g_main_context_iteration + 46
    frame #75: 0x00007ffff5be3919 libQt5Core.so.5`QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) + 105
    frame #76: 0x00007ffff5b8d48c libQt5Core.so.5`QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) + 316
    frame #77: 0x00007ffff5b95546 libQt5Core.so.5`QCoreApplication::exec() + 150
    frame #78: 0x0000555555570dbe plasmashell`___lldb_unnamed_symbol6$$plasmashell + 2910
    frame #79: 0x00007ffff55e3ce3 libc.so.6`__libc_start_main + 243
    frame #80: 0x000055555557126e plasmashell`_start + 46
(lldb)


I don't really understand what happened, I found nothing that could help on Internet, I tried to create a dummy user account to check if the issue is caused by a bad file in .config, .local, .cache, etc., but I have the same problem...
I really don't know what to do now, so I'd be glad to get some help.
Here are my specs :
- Motherboard Asus Maximus Extreme
- CPU : Intel Core 2 Quad Q9650
- 12GB RAM
- GPU : Nvidia Geforce GTX 550 Ti
- OS: Artix Linux

Which exact plasma version is this about?

I have exactly the same problem. Every time I log on to plasma desktop, plasmashell crashes.
Operating System: Kubuntu 19.04
KDE Plasma Version: 5.16.5
KDE Frameworks Version: 5.62.0
Qt Version: 5.12.2
Kernel Version: 5.0.0-32-generic
OS Type: 64-bit
Processors: 2 × Intel® Pentium® CPU P6200 @ 2.13GHz
Memory: 3.7 GiB of RAM

How about upgrading to 19.10? You would get a newer Plasma version. 19.04 is not LTS, so no reason not to upgrade.