Thanks. The fix worked for me.

It's hard to believe that such disruptive bug got past testing unnoticed...

Here is your solution/fix to this issue.

You need to downgrade and install this package by running this command, then reboot and all should be good to go!

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sudo apt install libkwaylandserver5=5.19.5-0xneon+20.04+focal+build10

same problem here. I tried the suggested downgrade, but I got a temporary failure of remote repo.
EDIT
solved: enabled netwoking e installed downgrade!
Thanks!

But when KDE Neon will definitively fix this issue? Meanwhile we must pin that library, I suppose.

That you very much for the fix!

Would like to know what were the exact steps (step by step) on how you got that solution. Just a matter of learning more things.

Once again thanks.

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apt-get install libkwaylandserver5=5.19.5-0xneon+20.04+focal+build10


Did the trick, thanks man !

as a pretty advanced linux user this took me 4 hours of debugging until I got to this thread.
still no real fix for those who updated early
in my 10 years of using kubuntu and almost always having at least one system on the unreleased ubuntu-next something like that never happened.
Just got a kde slimbook with kde neon preinstalled and this happened after 2 days of trying to use it.
I think I might not recommend kde neon to others but rather go back to kubuntu...

duns wrote:same problem here. I tried the suggested downgrade, but I got a temporary failure of remote repo.
EDIT
solved: enabled netwoking e installed downgrade!
Thanks!

But when KDE Neon will definitively fix this issue? Meanwhile we must pin that library, I suppose.

There is a little more information on Facebook.

A bad snapshot today caused an incomplete build to get into user editions. If you are affected downgrade with

sudo apt-get install libkwaylandserver5=5.19.5-0xneon+20.04+focal+build10

I assume that any bad packages were removed from the user edition repositories so don't think there will be a need to pin the library.

milikitato wrote:That you very much for the fix!

Would like to know what were the exact steps (step by step) on how you got that solution. Just a matter of learning more things.

Once again thanks.

Hi milikitato,

I will try and explain the process I went through

Found the problem on the forum and was able to confirm I had he same error by looking in $HOME/.xsession-errors or /var/log/Xorg.0.log can't remember exactly which file it was but these are the first port of call for X errors.

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kwin: symbol lookup error: /usr/lib/x86_64-linux-gnu/libkwin.so.5: undefined symbol: _ZN14KWaylandServer17XdgShellInterface14surfaceCreatedEPNS_24XdgShellSurfaceInterfaceE


I am not sure how familiar you are with C/C++ and compiled binaries/libraries but the error message is basically saying a function/method declaration could not be found. The symbol is the decorated/mangled name which is not the easiest to read but there is still some useful information for example KWaylandServer

Based on the error and that it happened after a system upgrade I suspected an incompatible library was installed.

I looked at the apt logs (/var/log/apt) and in particular the term.log. The last update will be at the end of the file and I could see there was only one package that mentioned KWaylandServer installed with my update (libkwaylandserver5).

The log also contained the previous version being updated.

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Preparing to unpack .../57-libkwaylandserver5_5.20.0-0xneon+20.04+focal+build11_amd64.deb ...
Unpacking libkwaylandserver5:amd64 (5.20.0-0xneon+20.04+focal+build11) over (5.19.5-0xneon+20.04+focal+build10) ...


I hoped downgrading this package would be enough to fix the issue.

And note installing an older package requires the full version to be specified.

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apt-get install libkwaylandserver5=5.19.5-0xneon+20.04+focal+build10


If this did not fix the problem I would have continued rolling back the packages from the bad update until the issue went away. Not sure if there is a nice way to rollback an entire update because it would have been rather painful to do each package individually.

nm is a useful command if you what examine symbols in a library

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nm -D /usr/lib/x86_64-linux-gnu/libkwin.so.5 | grep _ZN14KWaylandServer17XdgShellInterface14surfaceCreatedEPNS_24XdgShellSurfaceInterfaceE
                 U _ZN14KWaylandServer17XdgShellInterface14surfaceCreatedEPNS_24XdgShellSurfaceInterfaceE

nm -D /usr/lib/x86_64-linux-gnu/libKWaylandServer.so.5 | grep _ZN14KWaylandServer17XdgShellInterface14surfaceCreatedEPNS_24XdgShellSurfaceInterfaceE
0000000000073660 T _ZN14KWaylandServer17XdgShellInterface14surfaceCreatedEPNS_24XdgShellSurfaceInterfaceE


The first run on libkwin.so.5 shows the symbol is undefined and will be provided in another library (U at start of output).

The second on libKWaylandServer.so.5 shows the symbol is defined in this library, and if this was run on the bad version of the library it would not have existed.

I am not sure what exactly changed in the libKWaylandServer.so.5 but maybe the method was removed or changed slightly so the decorated symbol was different when recompiled.

Anyway hope that is what you are looking for milikitato.

derEremit wrote:as a pretty advanced linux user this took me 4 hours of debugging until I got to this thread.
still no real fix for those who updated early
in my 10 years of using kubuntu and almost always having at least one system on the unreleased ubuntu-next something like that never happened.
Just got a kde slimbook with kde neon preinstalled and this happened after 2 days of trying to use it.
I think I might not recommend kde neon to others but rather go back to kubuntu...

I have been using neon for sometime and this the first time I have experienced an issue that broken the UI in the user edition. I actually moved from kubuntu to neon and find it much more stable and a better kde experience.

It was clearly a mistake and of course unfortunate it happened especially that it broken the UI so made fixing it a bit cumbersome.

Downgrading fixed it for me too. Thanks a lot! Was on tight work deadlines and panicked for solid ~5 minutes.

markfergy wrote:I had the same issue and based on the symbol error I identified the libkwaylandserver5 package as the culprit.

A new version of this package was installed in the upgrade that caused the problem.

I downgraded the libkwaylandserver5 package to the previous version 5.19.5-0xneon+20.04+focal+build10 which fixed the issue for me

Run this as root to downgrade

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apt-get install libkwaylandserver5=5.19.5-0xneon+20.04+focal+build10


Will hold off any future upgrade until a fix is out.

Muchas gracias. Esto funcionó para mí también.