Hi,
Every now and then I lose the ability to use the middle mouse button. Clicking on it doesn't produce anything.
Furthermore, when this problem starts to appear others sympthomps arises. Some of them are:
1. When saving some files from within chromium, kdialog window keeps minutes to appear and the subsequent download waits a few seconds before actually starting.
2. KTP starts to take ages trying to connect to a xmpp server and when trying to contact some buddy, ktp-text-ui stalls forever.
3. Opening dolphin takes ages.

All I can do is logging out and logging in again.

How may I obtain some evidence of the cause of the problem?
dbus seems to be running as I can connect to it via qdbusviewer without delays.

Any clues?

open ksysguard and look at the cpu, IO read and write columns, the IO ones you may need to add by right clicking on the column headers - this should show you if any process(s) is/are eating up your resources.

also check if swap is being used instead of ram by running the free command in Konsole, on the swap line the free amount should be pretty close to the total swap amount

google01103 wrote:open ksysguard and look at the cpu, IO read and write columns, the IO ones you may need to add by right clicking on the column headers - this should show you if any process(s) is/are eating up your resources.

also check if swap is being used instead of ram by running the free command in Konsole, on the swap line the free amount should be pretty close to the total swap amount

I really don't have high memory pressure as I still have ~2G of free physical memory and the system is overall smooth and responsive. I searched through logfiles to look for processes eventually oom killed in the past, but didn't find any. I have only found usb errors still hanging around, most likely triggered by a faulty usb hub hardware.
I have to say that mine is not a classic setup as I have a bunch of monitors hooked to two graphics cards each of which drives a seat with its own independent kde-session on top of it. The two kde sessions (also on different X servers) are linked together using synergy software. I use this setup since a few years now and never experienced the aformentioned problems until a few weeks ago.

I might try to add KDE_DEBUG=1 at system startup and see if it will be of any help.

Update: I've just found out that I have many kf5 packages still installed just to try the new plasma5. Now I removed them..

It was KDED. I restarted kded and the system is up and running again without any sort of problem.
Now I'd like to get a clue on what is the cause of this kded hanging as I guess It will happen again..

kded keeps several daemon modules running, see "kcmshell4 kded" (resp. "kcmshell5 kded")
Does you're CPU 8or one core) spike in such occasions?

If not, look at the enabled daemons and see whether you can spot a "suspicious" one.