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Re: KDE hang? (not computer, not X11?)

On Saturday, 2017-03-04, 13:23:37, Mark Knecht wrote:
> Hi all,
>    I experienced a rather weird hang yesterday which logically seemed like
> a KDE problem but I'm unsure. No long-term lasting problems resulted but I
> wondered how to debug it or just best deal with it if it happens again.
> Thanks in advance for any ideas.
>    The machine is Gentoo, mostly stable with kde-meta-16.08.3 installed and
> generally updated every couple of days or so.
>    The symptoms of the event were:
> 1) The machine was up all day. I had been running 2 Virtualbox Windows VMs
> and had Matlab running in Linux, along with Chrome and other smaller apps.
> The machine was fine all day.
> 2) At 2PM local time the stock market closed so I shut down everything
> except 1 Windows VM which downloads data in the afternoon.
> 3) At some point KDE became non-responsive to either the mouse or keyboard.
> The mouse worked, the cursor moved, but nothing responded. The upper-left
> trigger to see all windows didn't work, the KDE menu was non-responsive and
> the Windows VM was non-responsive. However the programs running in the VM
> were still working and completed normally. I just had no apparent way to
> use KDE.

Could you still interact with the VM?

Do you have any regularily updating element on your desktop/panels, e.g. a 
clock? If yes, check if it still updates.

> 4) I was able to shell to the console using Ctrl-Alt-F1 where I could log
> in as root and also in my user account. Ctrl-Alt-F7 brought me back to X11
> which was still non-responsive.

Only mouse not responding or keyboard functions also?
E.g. Alt+F2 (KRunner)?

>    My question is was there something I might have tried to regain control
> of KDE instead of having to do the reboot? One thing I thought of after the
> event was maybe hot plug the mouse and/or keyboard to see if that work
> anything up.

It depends a bit, hence asking the questions above.

One cause of no longer being able to interact can be a global "grab".
X11 has the concept of application grabbing control of keyboard and/or mouse, 
e.g. popup windows such as menus do that.

If a program grabs control that way no other program can get mouse or keyboard 

The only way to recover from that is to get that "lock" released, e.g. by 
closing the window that grabbed input or killing the respective process.

If it is just a process hanging, e.g. plasmashell or kwin, then killing that 
and restarting it would already solve the problem.

Kevin Krammer, KDE developer, xdg-utils developer
KDE user support, developer mentoring

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