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kwin occasionally hangs, which looks like the system not responding to mouse clicks or key presses - although the mouse pointer still moves when you move the mouse!

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As described in the official Kwin documentation, a good way to go would be to try this either on a running terminal application or on a virtual console (i.e.: Ctrl+Alt+F1), :

DISPLAY=:0 kwin --replace
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+1, possibly the same effect as my solution (does kwin respond properly to sigint?), and certainly not worse. Also, a single command, so better. – Sparhawk Oct 11 '13 at 1:34
Don't you want to run it in the background? – Piotr Dobrogost Feb 22 '14 at 21:26

Similar to Robin Green's answer, but this does not require a terminal window to be open already. Instead, specify the display in which to start kwin from tty1. Hence,

Press Ctrl+Alt+F1 to access a terminal. Log in.

Type killall kwin. Then, type in DISPLAY=:0 kwin.

Press Ctrl+Alt+F7 to change back to your primary display.

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Shouldn't kwin be run in the background? – Piotr Dobrogost Apr 29 '14 at 19:09
@PiotrDobrogost If you like. It's running from tty1, which I wouldn't really use anyway, so I don't find backgrounding kwin necessary. – Sparhawk Apr 29 '14 at 22:53
up vote 2 down vote accepted

Press Ctrl+Alt+F1. Log in. Type killall kwin.

Press Ctrl+Alt+F7.

Quit all open applications until a terminal becomes visible. Hover the mouse over the terminal application. Type kwin &.

What's that, no terminal application open? Tough - you'll just have to reboot.

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I just added an answer that starts kwin from tty1, but I wonder if there is another way (that doesn't require a terminal window to be open already). Presumably you are getting keyboard input back after killing kwin, so after switching back to tty7, can you not just press alt-f2 an run kwin from there? – Sparhawk Dec 27 '12 at 1:32
Also, my two suggestions mean that you don't have to leave a terminal window open. – Sparhawk Dec 27 '12 at 1:34

Just do:

killall plasma-desktop
plasma-desktop &

you could have it all in a bash script in case you need it more times,

killall plasma-desktop
plasma-desktop &
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And how am I supposed to execute these commands if kwin won't let me do anything on the X display? – Robin Green Nov 7 '12 at 9:47

This actually works. It is a nasty bug but at least I can recover now.

In my case, there is no need to go back to the console login using ctrl+alt+f2 but using alt+f2 I can simply type killall plasma-desktop plasma-desktop and then using alt+f2 again,

I can run plasma-desktop. Could also be used in a script of course. This way I get back my mouse and I will not lose any work.

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I think that is a slightly different bug, because as I said, I could not use the keyboard at all except to switch to a virtual console. I do mean literally kwin, not plasma-desktop. – Robin Green Nov 18 '12 at 17:23

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