I have frequent crashes in KDE Neon and in Kubuntu 17.10 (https://ubuntuforums.org/showthread.php?t=2377192&p=13711851#post13711851) (not in 17.04) and in Pclinuxos KDE Desktop (https://www.pclinuxos.com/forum/index.php/topic,144325.msg1232845.html#msg1232845) .
I don't undestarnd why, but I believe that is something in recent KDE plasma updates (Kubuntu 17.04 worked fine, without crashes). I have crashes also in another PC with PClinuxOs KDE Desktop.
On Kubuntu and Pclos forums I did not get help, can you help me?
For example, which logs should i look for useful traces?
I believe this is something that has to do with a) the display or/and b) the internet connection.
Thank you

Maybe interesting (from .xsession-errrors)

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QDBusAbstractAdaptor: Cannot relay signal KDEDModule::moduleDeleted(KDEDModule*): Pointers are not supported: KDEDModule*
startkde: Done.
QDBusAbstractAdaptor: Cannot relay signal KDEDModule::moduleDeleted(KDEDModule*): Pointers are not supported: KDEDModule*
QDBusAbstractAdaptor: Cannot relay signal KDEDModule::moduleDeleted(KDEDModule*): Pointers are not supported: KDEDModule*
QDBusAbstractAdaptor: Cannot relay signal KDEDModule::moduleDeleted(KDEDModule*): Pointers are not supported: KDEDModule*
QDBusAbstractAdaptor: Cannot relay signal KDEDModule::moduleDeleted(KDEDModule*): Pointers are not supported: KDEDModule*
bluedevil: Destroyed
QDBusAbstractAdaptor: Cannot relay signal KDEDModule::moduleDeleted(KDEDModule*): Pointers are not supported: KDEDModule*
QDBusAbstractAdaptor: Cannot relay signal KDEDModule::moduleDeleted(KDEDModule*): Pointers are not supported: KDEDModule*
QDBusAbstractAdaptor: Cannot relay signal KDEDModule::moduleDeleted(KDEDModule*): Pointers are not supported: KDEDModule*
QDBusAbstractAdaptor: Cannot relay signal KDEDModule::moduleDeleted(KDEDModule*): Pointers are not supported: KDEDModule*
QDBusAbstractAdaptor: Cannot relay signal KDEDModule::moduleDeleted(KDEDModule*): Pointers are not supported: KDEDModule*
QDBusAbstractAdaptor: Cannot relay signal KDEDModule::moduleDeleted(KDEDModule*): Pointers are not supported: KDEDModule*
QDBusAbstractAdaptor: Cannot relay signal KDEDModule::moduleDeleted(KDEDModule*): Pointers are not supported: KDEDModule*
QDBusAbstractAdaptor: Cannot relay signal KDEDModule::moduleDeleted(KDEDModule*): Pointers are not supported: KDEDModule*
QDBusAbstractAdaptor: Cannot relay signal KDEDModule::moduleDeleted(KDEDModule*): Pointers are not supported: KDEDModule*
QDBusAbstractAdaptor: Cannot relay signal KDEDModule::moduleDeleted(KDEDModule*): Pointers are not supported: KDEDModule*
QDBusAbstractAdaptor: Cannot relay signal KDEDModule::moduleDeleted(KDEDModule*): Pointers are not supported: KDEDModule*
QDBusAbstractAdaptor: Cannot relay signal KDEDModule::moduleDeleted(KDEDModule*): Pointers are not supported: KDEDModule*
QDBusAbstractAdaptor: Cannot relay signal KDEDModule::moduleDeleted(KDEDModule*): Pointers are not supported: KDEDModule*
QThread: Destroyed while thread is still running
QDBusAbstractAdaptor: Cannot relay signal KDEDModule::moduleDeleted(KDEDModule*): Pointers are not supported: KDEDModule*
QDBusAbstractAdaptor: Cannot relay signal KDEDModule::moduleDeleted(KDEDModule*): Pointers are not supported: KDEDModule*
KCrash: Attempting to start /usr/bin/kdeinit5 from kdeinit
Warning: connect() failed: : No such file or directory
KCrash: Attempting to start /usr/bin/kdeinit5 directly
KCrash: crashing... crashRecursionCounter = 2
KCrash: Application Name = kdeinit5 path = /usr/bin pid = 1834
KCrash: Arguments: /usr/bin/kdeinit5
kdeinit5: preparing to launch '/usr/lib/x86_64-linux-gnu/libexec/kf5/klauncher'
kdeinit5: Launched KLauncher, pid = 5210, result = 0
QXcbConnection: Could not connect to display :0
kdeinit5: Communication error with launcher. Exiting!

I looked at your specs on the Ubuntu thread and it looks like you have a Kaby Lake CPU architecture if I am not mistaken. There is a problem with Kaby Lake and Skylake regarding hyperthreading which can cause serious problems. http://www.zdnet.com/article/debian-lin ... threading/

From the above link, to check if hyperthreading is enabled, try the following terminal command

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grep -q '^flags.*[[:space:]]ht[[:space:]]' /proc/cpuinfo && \ echo "Hyper-threading is supported"

If you have hyperthreading enabled, then the workaround is to disable hyperthreading in your BIOS/UEFI.

Thank you. In Kubuntu:

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duns@duns-neos:~$ grep -q '^flags.*[[:space:]]ht[[:space:]]' /proc/cpuinfo && \ echo "Hyper-threading is supported"
No command ' echo' found, did you mean:
 Command 'aecho' from package 'netatalk' (universe)
 Command 'echo' from package 'coreutils' (main)
 echo: command not found


In effect in BIOS hyperthreading was enabled, now is disabled.
We will see, now. Thank you

Unfortunately, no, it was not enough to disable hyperthreading in BIOS: other crashes occurred
Moreover, Pclinuxos is not debian, and I have crashes also on Pclinuxos...

But one thing is noteworthy: crashes are now less frequent, probably a sign that that setting was one of the causes of the problem, I believe. In my opinion there is another cause, in recent versions of plasma 5.

This night I left the PC on, with open clementine (crashes happen mostly in times of inactivity, so I left something active). This morning, moving the mouse appeared to me the screensaver login screen, I typed the password and has accepted it, but then: black screen, I saw only the mouse cursor; pressing ctrl + esc showed me the system monitor window, but the screen remained black. Then alt + stamp + r and alt + stamp + e: login screen and then I turned off.

My problem looks like this https://bugs.freedesktop.org/show_bug.cgi?id=92077#c31.
Can you help me?

Do you have a nvidia graphics card? If so have you installed the nvidia driver?

Have you tried to update to the latest kernel?

Thank you, gfielding.
1) Today I have updated the kernel in Kubuntu (now is 4.13). Only today, not yesteday.
2) My graphic card :
"*-display
description: VGA compatible controller
product: Intel Corporation
vendor: Intel Corporation
physical id: 2
bus info: pci@0000:00:02.0
version: 04
width: 64 bits
clock: 33MHz
capabilities: pciexpress msi pm vga_controller bus_master cap_list rom
configuration: driver=i915 latency=0
resources: irq:123 memory:de000000-deffffff memory:c0000000-cfffffff ioport:f000(size=64) memory:c0000-dffff"
An Intel graphic card

3) Yesterday I have added "i915.enable_rc6=0" in /etc/default/grub at the line GRUB_CMDLINE_LINUX_DEFAULT="quiet splash" so that it looks like:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash i915.enable_rc6=0".
So there is a new fact, after adding that string to /etc /default/grub: the problem narrows to the black screen, after a period of inactivity, and after typing in the password to the login screensaver (login screensaver working).
For the rest all works: there is internet connection, amule works, works KDE connect (I can start music from smartphone),
there is only the black screen, I just see the mouse cursor and if I press ctrl + esc I see the system monitor window. Then I must make a forced logout with alt + stamp + r and alt + stamp + e.
One step forward was made: it remains only the black screen.

Today I have added/created a file: /etc/X11/xorg.conf.d/20-intel.conf
and added this lines
1) before:

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Section "Device"
  Identifier  "Intel Graphics"
  Driver      "intel"
EndSection


2) after (because there was a bit of flickering with prev config):

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Section "Device"
  Identifier  "Intel Graphics"
  #Driver  "intel"
  Driver "modesetting"
  Option "AccelMethod" "glamor"
  Option "Backlight" "intel_backlight"
EndSection


And I have installed from synaptic intel-gpu-tools (but I don't konw how use it)

What I should control (logs ?), and what I should do, now?
Thank you

Probably the problem is the Kernel (4.13): https://www.kubuntuforums.net/showthread.php/72652-eeepc-after-boot-half-black-screen?p=407380&viewfull=1#post407380.
I will try with 4.10.

No: today I left inactive the pc for 4 hours, with the kernel 4.10.37, and on the return I still had black screen with the mouse cursor, with the possibility of displaying the windows of active programs (alt + tab): at this time I am writing while this strange crash is happening, with amule and internet working perfectly.
No, seems not a kernel problem!

Now I have this 20-intel.conf

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Section "Device"
  Identifier  "Intel Graphics"
  #Driver  "intel"
  Driver "modesetting"
  Option "TearFree" "true"
  Option "AccelMethod" "sna"
  Option "NoAccel" "True"
  Option "Backlight" "intel_backlight"
EndSection

My graphic card:

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Graphics:  Card: Intel HD Graphics 630
           Display Server: x11 (X.Org 1.19.5 ) driver: modesetting Resolution: 1280x1024@60.02hz
           OpenGL: renderer: llvmpipe (LLVM 5.0, 256 bits) version: 3.3 Mesa 17.2.2


And grub file in /etc/default

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GRUB_CMDLINE_LINUX_DEFAULT="quiet splash i915.enable_rc6=0 i915.enable_fbc=1 i915.lvds_downclock=1 i915.semaphores=1"

Solved with a creation of a new user!