For example it's an equivalent of 4071 lines in 10 hours.

A workaround would be to disable this logging category by putting a line like

kscreen.xcb.helper=false

in your ~/.config/QtProject/qtlogging.ini.

The root cause seems to be X acting weird, but I'll let Dan comment on that.

Thanks for the trick Sebastian,

Unfortunately I already have those flag

kscreen.kded=false
kscreen.debug=false
kscreen.edid=false
kscreen.fake=false
kscreen.qscreen=false
kscreen.xcb_helper=false
kscreen.xrandr=false
kscreen.xrandr11=false

After looking twice I was small difference 
kscreen.xcb_helper=false != kscreen.xcb.helper=false

so I'm adding the last one

Since I put the right var in ~/.config/QtProject/qtlogging.ini
 kscreen.xcb.helper=false

There's no more output on normal condition, and they appear if I make them true in kdebugdialog.

So the problem is more about the component who write ~/.config/QtProject/qtlogging.ini
But I've no idea which one is

That file is written by the user (or an app called kdebugsettings in some cases), but it's not a default config file. It seems like your system enables debugging output somewhere, so you have to switch it off again. The message is not displayed by default as far as I can tell.

Ok I've erase the file, and test kdebugdialog5 and kdedebugdialog (the qt4)
none of them create it.

the application responsible to create it is 
kdebugsettings-16.07.70git-12.1.x86_64


I'm moving to the right component.

Git commit 8d274b043c252ffc69f86caee752f30d31f7f05e by Sebastian Kügler.
Committed on 18/04/2016 at 19:47.
Pushed by sebas into branch 'Applications/16.04'.

Fix category of xcb helper for libkscreen

M  +1    -1    data/kde.categories

http://commits.kde.org/kdebugsettings/8d274b043c252ffc69f86caee752f30d31f7f05e

Git commit a28abfcf5780858cabae675944f0d27d3416a297 by Sebastian Kügler.
Committed on 18/04/2016 at 19:46.
Pushed by sebas into branch 'master'.

Fix category of xcb helper for libkscreen

M  +1    -1    data/kde.categories

http://commits.kde.org/kdebugsettings/a28abfcf5780858cabae675944f0d27d3416a297

The workaround does not work for me. org.kde.KScreen is still spamming my logs.

Furthermore, the bug is *not* fixed Plasma 5.8.2 LTS, Applications 16.08 and KDE Frameworks 5.26 LTS on openSUSE Leap 42.2. Whenever the brightness of my screen is changed, there still tons of messages from org.kde.KScreen kscreen.xcb.helper. 

Even adding the rule "*=false" does not help.

Then you're doing it wrong, I'm afraid. We're not changing anything about the semantics of Qt's categorized logging. If it doesn't work for you using the correct syntax (*.debug=false to disable everything, not *=false), then that would be a bug in Qt (unlikely in this case), which should be reported against Qt, definitely check the documentation before, it's at http://doc.qt.io/qt-5/qloggingcategory.html#configuring-categories .

I can't just remove those messages, since we're actually using them to debug problems deep down in the stack, and they need to be fixed.

(In reply to Sebastian Kügler from comment #10)
> [...]
> I can't just remove those messages, since we're actually using them to debug
> problems deep down in the stack, and they need to be fixed.

Ah, okay, I thought the bug was fixed by setting the default to disable these debug messages.

> [...]
> Then you're doing it wrong, I'm afraid. 

I started kdebugsettings-16.08.2, verified that every kscreen entry is set to "Aus" (Off), pressed "OK" and even rebooted. I cannot image what I could have done wrong.

And I am not alone:
https://forum.kde.org/viewtopic.php?f=289&t=135992#p363934

> [...] definitely check the documentation before, it's at
> http://doc.qt.io/qt-5/qloggingcategory.html#configuring-categories .

I have read the documentation. "*=false" *is* correct to disable any logging:
 <category>[.<type>] = true|false

JFTR, I took a look at the source code from github:
* Since 1aa3eb98b22fbe5e690ca8f3096c6e3b712ac3d8, log.cpp calls QLoggingCategory::setFilterRules("kscreen.*=true") unless KSCREEN_LOGGING is set to "0" or "false" (case insensitive), and
* since f4d3e52e2e2497634a269faeab2d5d6eba0f3526, the logger is installed in backendmanager.cpp and backendlauncher/main.cpp.
So, a filter rule is installed that enables logging for kscreen overriding qtlogging.ini but is never removed later on.

The new workaround is to set the rule in your environment, e.g., by adding 
export QT_LOGGING_RULES="kscreen.*=false"
to your "~/.profile".

Please don't just re-open bugreports, it makes my life managing kscreen bugs much harder.

You can disable the logging by setting the KSCREEN_LOGGING var to 0 or false in your environment. As I said, the info is *not* useless, as it helped to identify a large number of pretty serious bugs already, and that's why I'm hesitant to disable it.

(In reply to Sebastian Kügler from comment #13)
> Please don't just re-open bugreports, it makes my life managing kscreen bugs
> much harder.

Then, please fix the bug or mark it as wontfix! kscreen pitilessly overrides any decision the user made via kdebugsettings and fills the log at insane rate. And this problem is still *not* fixed. kdebugsettings was fixed to use the correct category but now kscreen ignores that.

> [...]
> As I said, the info is *not* useless, as it helped to
> identify a large number of pretty serious bugs already, and that's why I'm
> hesitant to disable it.

So, you are saying that you cannot identify bugs if kscreen does not log both in the syslog/journal *and* in ~/.local/share/kscreen/kscreen.log? Please tell me more...

I can just concur to that : Here's a simple backlight event

in system journal 

Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper: RRNotify_OutputProperty (ignored)
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Output:  547
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Property:  Backlight
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     State (newValue, Deleted):  0
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper: RRNotify_OutputProperty (ignored)
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Output:  547
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Property:  Backlight
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     State (newValue, Deleted):  0
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper: RRNotify_OutputProperty (ignored)
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Output:  547
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Property:  Backlight
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     State (newValue, Deleted):  0
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper: RRNotify_OutputProperty (ignored)
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Output:  547
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Property:  Backlight
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     State (newValue, Deleted):  0
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper: RRNotify_OutputProperty (ignored)
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Output:  547
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Property:  Backlight
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     State (newValue, Deleted):  0
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper: RRNotify_OutputProperty (ignored)
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Output:  547
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Property:  Backlight
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     State (newValue, Deleted):  0
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper: RRNotify_OutputProperty (ignored)
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Output:  547
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Property:  Backlight
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     State (newValue, Deleted):  0
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper: RRNotify_OutputProperty (ignored)
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Output:  547
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Property:  Backlight
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     State (newValue, Deleted):  0
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper: RRNotify_OutputProperty (ignored)
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Output:  547
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Property:  Backlight
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     State (newValue, Deleted):  0
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper: RRNotify_OutputProperty (ignored)
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Output:  547
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Property:  Backlight
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     State (newValue, Deleted):  0
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper: RRNotify_OutputProperty (ignored)
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Output:  547
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Property:  Backlight
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     State (newValue, Deleted):  0
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper: RRNotify_OutputProperty (ignored)
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Output:  547
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Property:  Backlight
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     State (newValue, Deleted):  0
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper: RRNotify_OutputProperty (ignored)
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Output:  547
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Property:  Backlight
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     State (newValue, Deleted):  0
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper: RRNotify_OutputProperty (ignored)
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Output:  547
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Property:  Backlight
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     State (newValue, Deleted):  0
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper: RRNotify_OutputProperty (ignored)
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Output:  547
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Property:  Backlight
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     State (newValue, Deleted):  0
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper: RRNotify_OutputProperty (ignored)
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Output:  547
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Property:  Backlight
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     State (newValue, Deleted):  0
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper: RRNotify_OutputProperty (ignored)
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Output:  547
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Property:  Backlight
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     State (newValue, Deleted):  0
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper: RRNotify_OutputProperty (ignored)
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Output:  547
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Property:  Backlight
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     State (newValue, Deleted):  0
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper: RRNotify_OutputProperty (ignored)
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Output:  547
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Property:  Backlight
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     State (newValue, Deleted):  0
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper: RRNotify_OutputProperty (ignored)
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Output:  547
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Property:  Backlight
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     State (newValue, Deleted):  0
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper: RRNotify_OutputProperty (ignored)
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Output:  547
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Property:  Backlight
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     State (newValue, Deleted):  0
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper: RRNotify_OutputProperty (ignored)
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Output:  547
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Property:  Backlight
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     State (newValue, Deleted):  0
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper: RRNotify_OutputProperty (ignored)
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Output:  547
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Property:  Backlight
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     State (newValue, Deleted):  0
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper: RRNotify_OutputProperty (ignored)
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Output:  547
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Property:  Backlight
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     State (newValue, Deleted):  0
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper: RRNotify_OutputProperty (ignored)
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Output:  547
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Property:  Backlight
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     State (newValue, Deleted):  0
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper: RRNotify_OutputProperty (ignored)
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Output:  547
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Property:  Backlight
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     State (newValue, Deleted):  0
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper: RRNotify_OutputProperty (ignored)
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Output:  547
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Property:  Backlight
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     State (newValue, Deleted):  0
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper: RRNotify_OutputProperty (ignored)
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Output:  547
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Property:  Backlight
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     State (newValue, Deleted):  0
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper: RRNotify_OutputProperty (ignored)
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Output:  547
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Property:  Backlight
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     State (newValue, Deleted):  0
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper: RRNotify_OutputProperty (ignored)
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Output:  547
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Property:  Backlight
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     State (newValue, Deleted):  0
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper: RRNotify_OutputProperty (ignored)
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Output:  547
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Property:  Backlight
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     State (newValue, Deleted):  0
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper: RRNotify_OutputProperty (ignored)
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Output:  547
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     Property:  Backlight
Jan 05 19:39:21 qt-kt.labaroche.ioda.net org.kde.KScreen[2351]: kscreen.xcb.helper:     State (newValue, Deleted):  0

and the same is also registered in ~/.local/share/kscreen/kscreen.log

05.01.2017 19:39:21.028 ; xcb.helper ;  : RRNotify_OutputProperty (ignored)
05.01.2017 19:39:21.028 ; xcb.helper ;  :       Output:  547
05.01.2017 19:39:21.029 ; xcb.helper ;  :       Property:  Backlight
05.01.2017 19:39:21.029 ; xcb.helper ;  :       State (newValue, Deleted):  0
05.01.2017 19:39:21.029 ; xcb.helper ;  : RRNotify_OutputProperty (ignored)
05.01.2017 19:39:21.029 ; xcb.helper ;  :       Output:  547
05.01.2017 19:39:21.029 ; xcb.helper ;  :       Property:  Backlight
05.01.2017 19:39:21.029 ; xcb.helper ;  :       State (newValue, Deleted):  0
05.01.2017 19:39:21.064 ; xcb.helper ;  : RRNotify_OutputProperty (ignored)
05.01.2017 19:39:21.064 ; xcb.helper ;  :       Output:  547
05.01.2017 19:39:21.064 ; xcb.helper ;  :       Property:  Backlight
05.01.2017 19:39:21.064 ; xcb.helper ;  :       State (newValue, Deleted):  0
05.01.2017 19:39:21.064 ; xcb.helper ;  : RRNotify_OutputProperty (ignored)
05.01.2017 19:39:21.065 ; xcb.helper ;  :       Output:  547
05.01.2017 19:39:21.065 ; xcb.helper ;  :       Property:  Backlight
05.01.2017 19:39:21.065 ; xcb.helper ;  :       State (newValue, Deleted):  0
05.01.2017 19:39:21.080 ; xcb.helper ;  : RRNotify_OutputProperty (ignored)
05.01.2017 19:39:21.080 ; xcb.helper ;  :       Output:  547
05.01.2017 19:39:21.080 ; xcb.helper ;  :       Property:  Backlight
05.01.2017 19:39:21.080 ; xcb.helper ;  :       State (newValue, Deleted):  0
05.01.2017 19:39:21.081 ; xcb.helper ;  : RRNotify_OutputProperty (ignored)
05.01.2017 19:39:21.081 ; xcb.helper ;  :       Output:  547
05.01.2017 19:39:21.081 ; xcb.helper ;  :       Property:  Backlight
05.01.2017 19:39:21.081 ; xcb.helper ;  :       State (newValue, Deleted):  0
05.01.2017 19:39:21.096 ; xcb.helper ;  : RRNotify_OutputProperty (ignored)
05.01.2017 19:39:21.097 ; xcb.helper ;  :       Output:  547
05.01.2017 19:39:21.097 ; xcb.helper ;  :       Property:  Backlight
05.01.2017 19:39:21.097 ; xcb.helper ;  :       State (newValue, Deleted):  0
05.01.2017 19:39:21.097 ; xcb.helper ;  : RRNotify_OutputProperty (ignored)
05.01.2017 19:39:21.097 ; xcb.helper ;  :       Output:  547
05.01.2017 19:39:21.097 ; xcb.helper ;  :       Property:  Backlight
05.01.2017 19:39:21.097 ; xcb.helper ;  :       State (newValue, Deleted):  0
05.01.2017 19:39:21.112 ; xcb.helper ;  : RRNotify_OutputProperty (ignored)
05.01.2017 19:39:21.112 ; xcb.helper ;  :       Output:  547
05.01.2017 19:39:21.112 ; xcb.helper ;  :       Property:  Backlight
05.01.2017 19:39:21.112 ; xcb.helper ;  :       State (newValue, Deleted):  0
05.01.2017 19:39:21.113 ; xcb.helper ;  : RRNotify_OutputProperty (ignored)
05.01.2017 19:39:21.113 ; xcb.helper ;  :       Output:  547
05.01.2017 19:39:21.113 ; xcb.helper ;  :       Property:  Backlight
05.01.2017 19:39:21.113 ; xcb.helper ;  :       State (newValue, Deleted):  0
05.01.2017 19:39:21.128 ; xcb.helper ;  : RRNotify_OutputProperty (ignored)
05.01.2017 19:39:21.128 ; xcb.helper ;  :       Output:  547
05.01.2017 19:39:21.128 ; xcb.helper ;  :       Property:  Backlight
05.01.2017 19:39:21.128 ; xcb.helper ;  :       State (newValue, Deleted):  0
05.01.2017 19:39:21.128 ; xcb.helper ;  : RRNotify_OutputProperty (ignored)
05.01.2017 19:39:21.128 ; xcb.helper ;  :       Output:  547
05.01.2017 19:39:21.128 ; xcb.helper ;  :       Property:  Backlight
05.01.2017 19:39:21.128 ; xcb.helper ;  :       State (newValue, Deleted):  0
05.01.2017 19:39:21.143 ; xcb.helper ;  : RRNotify_OutputProperty (ignored)
05.01.2017 19:39:21.143 ; xcb.helper ;  :       Output:  547
05.01.2017 19:39:21.144 ; xcb.helper ;  :       Property:  Backlight
05.01.2017 19:39:21.144 ; xcb.helper ;  :       State (newValue, Deleted):  0
05.01.2017 19:39:21.144 ; xcb.helper ;  : RRNotify_OutputProperty (ignored)
05.01.2017 19:39:21.144 ; xcb.helper ;  :       Output:  547
05.01.2017 19:39:21.144 ; xcb.helper ;  :       Property:  Backlight
05.01.2017 19:39:21.144 ; xcb.helper ;  :       State (newValue, Deleted):  0
05.01.2017 19:39:21.159 ; xcb.helper ;  : RRNotify_OutputProperty (ignored)
05.01.2017 19:39:21.159 ; xcb.helper ;  :       Output:  547
05.01.2017 19:39:21.159 ; xcb.helper ;  :       Property:  Backlight
05.01.2017 19:39:21.159 ; xcb.helper ;  :       State (newValue, Deleted):  0
05.01.2017 19:39:21.159 ; xcb.helper ;  : RRNotify_OutputProperty (ignored)
05.01.2017 19:39:21.159 ; xcb.helper ;  :       Output:  547
05.01.2017 19:39:21.159 ; xcb.helper ;  :       Property:  Backlight
05.01.2017 19:39:21.159 ; xcb.helper ;  :       State (newValue, Deleted):  0
05.01.2017 19:39:21.176 ; xcb.helper ;  : RRNotify_OutputProperty (ignored)
05.01.2017 19:39:21.176 ; xcb.helper ;  :       Output:  547
05.01.2017 19:39:21.176 ; xcb.helper ;  :       Property:  Backlight
05.01.2017 19:39:21.176 ; xcb.helper ;  :       State (newValue, Deleted):  0
05.01.2017 19:39:21.177 ; xcb.helper ;  : RRNotify_OutputProperty (ignored)
05.01.2017 19:39:21.177 ; xcb.helper ;  :       Output:  547
05.01.2017 19:39:21.177 ; xcb.helper ;  :       Property:  Backlight
05.01.2017 19:39:21.177 ; xcb.helper ;  :       State (newValue, Deleted):  0
05.01.2017 19:39:21.192 ; xcb.helper ;  : RRNotify_OutputProperty (ignored)
05.01.2017 19:39:21.192 ; xcb.helper ;  :       Output:  547
05.01.2017 19:39:21.192 ; xcb.helper ;  :       Property:  Backlight
05.01.2017 19:39:21.192 ; xcb.helper ;  :       State (newValue, Deleted):  0
05.01.2017 19:39:21.193 ; xcb.helper ;  : RRNotify_OutputProperty (ignored)
05.01.2017 19:39:21.193 ; xcb.helper ;  :       Output:  547
05.01.2017 19:39:21.193 ; xcb.helper ;  :       Property:  Backlight
05.01.2017 19:39:21.193 ; xcb.helper ;  :       State (newValue, Deleted):  0
05.01.2017 19:39:21.208 ; xcb.helper ;  : RRNotify_OutputProperty (ignored)
05.01.2017 19:39:21.208 ; xcb.helper ;  :       Output:  547
05.01.2017 19:39:21.208 ; xcb.helper ;  :       Property:  Backlight
05.01.2017 19:39:21.208 ; xcb.helper ;  :       State (newValue, Deleted):  0
05.01.2017 19:39:21.208 ; xcb.helper ;  : RRNotify_OutputProperty (ignored)
05.01.2017 19:39:21.208 ; xcb.helper ;  :       Output:  547
05.01.2017 19:39:21.208 ; xcb.helper ;  :       Property:  Backlight
05.01.2017 19:39:21.208 ; xcb.helper ;  :       State (newValue, Deleted):  0
05.01.2017 19:39:21.224 ; xcb.helper ;  : RRNotify_OutputProperty (ignored)
05.01.2017 19:39:21.224 ; xcb.helper ;  :       Output:  547
05.01.2017 19:39:21.224 ; xcb.helper ;  :       Property:  Backlight
05.01.2017 19:39:21.224 ; xcb.helper ;  :       State (newValue, Deleted):  0
05.01.2017 19:39:21.224 ; xcb.helper ;  : RRNotify_OutputProperty (ignored)
05.01.2017 19:39:21.225 ; xcb.helper ;  :       Output:  547
05.01.2017 19:39:21.225 ; xcb.helper ;  :       Property:  Backlight
05.01.2017 19:39:21.225 ; xcb.helper ;  :       State (newValue, Deleted):  0
05.01.2017 19:39:21.239 ; xcb.helper ;  : RRNotify_OutputProperty (ignored)
05.01.2017 19:39:21.239 ; xcb.helper ;  :       Output:  547
05.01.2017 19:39:21.239 ; xcb.helper ;  :       Property:  Backlight
05.01.2017 19:39:21.239 ; xcb.helper ;  :       State (newValue, Deleted):  0
05.01.2017 19:39:21.240 ; xcb.helper ;  : RRNotify_OutputProperty (ignored)
05.01.2017 19:39:21.240 ; xcb.helper ;  :       Output:  547
05.01.2017 19:39:21.240 ; xcb.helper ;  :       Property:  Backlight
05.01.2017 19:39:21.240 ; xcb.helper ;  :       State (newValue, Deleted):  0
05.01.2017 19:39:21.256 ; xcb.helper ;  : RRNotify_OutputProperty (ignored)
05.01.2017 19:39:21.256 ; xcb.helper ;  :       Output:  547
05.01.2017 19:39:21.257 ; xcb.helper ;  :       Property:  Backlight
05.01.2017 19:39:21.257 ; xcb.helper ;  :       State (newValue, Deleted):  0
05.01.2017 19:39:21.257 ; xcb.helper ;  : RRNotify_OutputProperty (ignored)
05.01.2017 19:39:21.257 ; xcb.helper ;  :       Output:  547
05.01.2017 19:39:21.257 ; xcb.helper ;  :       Property:  Backlight
05.01.2017 19:39:21.257 ; xcb.helper ;  :       State (newValue, Deleted):  0
05.01.2017 19:39:21.272 ; xcb.helper ;  : RRNotify_OutputProperty (ignored)
05.01.2017 19:39:21.272 ; xcb.helper ;  :       Output:  547
05.01.2017 19:39:21.272 ; xcb.helper ;  :       Property:  Backlight
05.01.2017 19:39:21.272 ; xcb.helper ;  :       State (newValue, Deleted):  0
05.01.2017 19:39:21.272 ; xcb.helper ;  : RRNotify_OutputProperty (ignored)
05.01.2017 19:39:21.272 ; xcb.helper ;  :       Output:  547
05.01.2017 19:39:21.272 ; xcb.helper ;  :       Property:  Backlight
05.01.2017 19:39:21.272 ; xcb.helper ;  :       State (newValue, Deleted):  0
05.01.2017 19:39:21.287 ; xcb.helper ;  : RRNotify_OutputProperty (ignored)
05.01.2017 19:39:21.288 ; xcb.helper ;  :       Output:  547
05.01.2017 19:39:21.288 ; xcb.helper ;  :       Property:  Backlight
05.01.2017 19:39:21.288 ; xcb.helper ;  :       State (newValue, Deleted):  0
05.01.2017 19:39:21.288 ; xcb.helper ;  : RRNotify_OutputProperty (ignored)
05.01.2017 19:39:21.288 ; xcb.helper ;  :       Output:  547
05.01.2017 19:39:21.288 ; xcb.helper ;  :       Property:  Backlight
05.01.2017 19:39:21.288 ; xcb.helper ;  :       State (newValue, Deleted):  0

I've tried to use all the trick to shutup all of this noise (Until I want to check and debug something, all of those are just killing my M2 ssd and use i/o and place for nothing)

I've 
QT_LOGGING_RULES=kscreen.*=false
and all off in kdebugsettings.

@Sebastian it would be reasonable to have the lower impact on user system by default, then having flags and bolts and nuts activable when debug is needed.

https://phabricator.kde.org/D3993 disables logging by default. It's a lot less necessary than when we introduced it now, so we can enable it only when needed.

Git commit 04a6483a01caaa17e476ac9e4a47725f0e1ca06f by Sebastian Kügler.
Committed on 11/01/2017 at 21:43.
Pushed by sebas into branch 'Plasma/5.8'.

disable logging to kscreen.log by default

Summary:
Most of the issues that this feature should uncover have been uncovered,
it makes sense to disable the logging (and futzing around with
QCategorizedLogging) by default, and only use it to debug specific
setups.

Test Plan: Adjusted autotests accordingly.

Reviewers: #plasma, mart

Reviewed By: mart

Subscribers: graesslin, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D3993
CHANGELOG:Disable logging to kscreen.log by default, re-enable with export KSCREEN_LOGGING=1

cherry-picked from cea4c63f84650efa4

M  +8    -0    autotests/testlog.cpp
M  +6    -4    src/log.cpp

https://commits.kde.org/libkscreen/04a6483a01caaa17e476ac9e4a47725f0e1ca06f

My journalctl log is full of this messages. I'm on plasma 5.12 with Arch. How can I disable this logging message?

Previous commit disabled kscreen log. If you did not manually enable it, the messages you see are not from kscreen.