plasma-discover uses 100% cpu and seems to hang/freeze for several minutes when cantor*.knsrc files reside in /etc/xdg STEPS TO REPRODUCE 1. install cantor 2. open discover OBSERVED RESULT the discover UI freezes for several minutes and these messages appear on stdout while plasma-discover memory consumption rises to about 800MB: org.kde.knewstuff.core: Could not find category "Cantor (Python 3)" org.kde.knewstuff.core: Could not find category "Cantor (KAlgebra)" org.kde.knewstuff.core: Could not find category "Cantor (Python 2)" org.kde.knewstuff.core: Could not find category "Cantor (Scilab)" org.kde.knewstuff.core: Could not find category "Cantor (Octave)" org.kde.knewstuff.core: Could not find category "Cantor (Sage)" org.kde.knewstuff.core: Could not find category "Cantor (Maxima)" org.kde.knewstuff.core: Could not find category "Cantor (R)" org.kde.knewstuff.core: Could not find category "Cantor (Lua)" org.kde.knewstuff.core: Could not find category "Cantor (Qalculate)" invalid kns backend! "/etc/xdg/cantor_scilab.knsrc" because: "All categories are missing" org.kde.plasma.libdiscover: Discarding invalid backend "cantor_scilab.knsrc" kns error "/etc/xdg/cantor_scilab.knsrc" "Invalid Cantor_scilab backend, contact your distributor." org.kde.knewstuff.core: Could not find category "Cantor (Python 3)" org.kde.knewstuff.core: Could not find category "Cantor (KAlgebra)" org.kde.knewstuff.core: Could not find category "Cantor (Python 2)" org.kde.knewstuff.core: Could not find category "Cantor (Scilab)" org.kde.knewstuff.core: Could not find category "Cantor (Octave)" org.kde.knewstuff.core: Could not find category "Cantor (Sage)" org.kde.knewstuff.core: Could not find category "Cantor (Maxima)" org.kde.knewstuff.core: Could not find category "Cantor (R)" org.kde.knewstuff.core: Could not find category "Cantor (Lua)" org.kde.knewstuff.core: Could not find category "Cantor (Qalculate)" invalid kns backend! "/etc/xdg/cantor_qalculate.knsrc" because: "All categories are missing" org.kde.plasma.libdiscover: Discarding invalid backend "cantor_qalculate.knsrc" kns error "/etc/xdg/cantor_qalculate.knsrc" "Invalid Cantor_qalculate backend, contact your distributor." org.kde.knewstuff.core: Could not find category "Cantor (Python 3)" org.kde.knewstuff.core: Could not find category "Cantor (KAlgebra)" org.kde.knewstuff.core: Could not find category "Cantor (Python 2)" org.kde.knewstuff.core: Could not find category "Cantor (Scilab)" org.kde.knewstuff.core: Could not find category "Cantor (Octave)" org.kde.knewstuff.core: Could not find category "Cantor (Sage)" org.kde.knewstuff.core: Could not find category "Cantor (Maxima)" org.kde.knewstuff.core: Could not find category "Cantor (R)" org.kde.knewstuff.core: Could not find category "Cantor (Lua)" org.kde.knewstuff.core: Could not find category "Cantor (Qalculate)" invalid kns backend! "/etc/xdg/cantor_sage.knsrc" because: "All categories are missing" org.kde.plasma.libdiscover: Discarding invalid backend "cantor_sage.knsrc" kns error "/etc/xdg/cantor_sage.knsrc" "Invalid Cantor_sage backend, contact your distributor." org.kde.knewstuff.core: Could not find category "Cantor (Python 3)" org.kde.knewstuff.core: Could not find category "Cantor (KAlgebra)" org.kde.knewstuff.core: Could not find category "Cantor (Python 2)" org.kde.knewstuff.core: Could not find category "Cantor (Scilab)" org.kde.knewstuff.core: Could not find category "Cantor (Octave)" org.kde.knewstuff.core: Could not find category "Cantor (Sage)" org.kde.knewstuff.core: Could not find category "Cantor (Maxima)" org.kde.knewstuff.core: Could not find category "Cantor (R)" org.kde.knewstuff.core: Could not find category "Cantor (Lua)" org.kde.knewstuff.core: Could not find category "Cantor (Qalculate)" invalid kns backend! "/etc/xdg/cantor_kalgebra.knsrc" because: "All categories are missing" org.kde.plasma.libdiscover: Discarding invalid backend "cantor_kalgebra.knsrc" kns error "/etc/xdg/cantor_kalgebra.knsrc" "Invalid Cantor_kalgebra backend, contact your distributor." org.kde.knewstuff.core: Could not find category "Cantor (Python 3)" org.kde.knewstuff.core: Could not find category "Cantor (KAlgebra)" org.kde.knewstuff.core: Could not find category "Cantor (Python 2)" org.kde.knewstuff.core: Could not find category "Cantor (Scilab)" org.kde.knewstuff.core: Could not find category "Cantor (Octave)" org.kde.knewstuff.core: Could not find category "Cantor (Sage)" org.kde.knewstuff.core: Could not find category "Cantor (Maxima)" org.kde.knewstuff.core: Could not find category "Cantor (R)" org.kde.knewstuff.core: Could not find category "Cantor (Lua)" org.kde.knewstuff.core: Could not find category "Cantor (Qalculate)" invalid kns backend! "/etc/xdg/cantor.knsrc" because: "All categories are missing" org.kde.plasma.libdiscover: Discarding invalid backend "cantor.knsrc" kns error "/etc/xdg/cantor.knsrc" "Invalid Cantor backend, contact your distributor." org.kde.knewstuff.core: Could not find category "Cantor (Python 3)" org.kde.knewstuff.core: Could not find category "Cantor (KAlgebra)" org.kde.knewstuff.core: Could not find category "Cantor (Python 2)" org.kde.knewstuff.core: Could not find category "Cantor (Scilab)" org.kde.knewstuff.core: Could not find category "Cantor (Octave)" org.kde.knewstuff.core: Could not find category "Cantor (Sage)" org.kde.knewstuff.core: Could not find category "Cantor (Maxima)" org.kde.knewstuff.core: Could not find category "Cantor (R)" org.kde.knewstuff.core: Could not find category "Cantor (Lua)" org.kde.knewstuff.core: Could not find category "Cantor (Qalculate)" invalid kns backend! "/etc/xdg/cantor_maxima.knsrc" because: "All categories are missing" org.kde.plasma.libdiscover: Discarding invalid backend "cantor_maxima.knsrc" kns error "/etc/xdg/cantor_maxima.knsrc" "Invalid Cantor_maxima backend, contact your distributor." org.kde.knewstuff.core: Could not find category "Cantor (Python 3)" org.kde.knewstuff.core: Could not find category "Cantor (KAlgebra)" org.kde.knewstuff.core: Could not find category "Cantor (Python 2)" org.kde.knewstuff.core: Could not find category "Cantor (Scilab)" org.kde.knewstuff.core: Could not find category "Cantor (Octave)" org.kde.knewstuff.core: Could not find category "Cantor (Sage)" org.kde.knewstuff.core: Could not find category "Cantor (Maxima)" org.kde.knewstuff.core: Could not find category "Cantor (R)" org.kde.knewstuff.core: Could not find category "Cantor (Lua)" org.kde.knewstuff.core: Could not find category "Cantor (Qalculate)" invalid kns backend! "/etc/xdg/cantor_lua.knsrc" because: "All categories are missing" org.kde.plasma.libdiscover: Discarding invalid backend "cantor_lua.knsrc" kns error "/etc/xdg/cantor_lua.knsrc" "Invalid Cantor_lua backend, contact your distributor." org.kde.knewstuff.core: Could not find category "Cantor (Python 3)" org.kde.knewstuff.core: Could not find category "Cantor (KAlgebra)" org.kde.knewstuff.core: Could not find category "Cantor (Python 2)" org.kde.knewstuff.core: Could not find category "Cantor (Scilab)" org.kde.knewstuff.core: Could not find category "Cantor (Octave)" org.kde.knewstuff.core: Could not find category "Cantor (Sage)" org.kde.knewstuff.core: Could not find category "Cantor (Maxima)" org.kde.knewstuff.core: Could not find category "Cantor (R)" org.kde.knewstuff.core: Could not find category "Cantor (Lua)" org.kde.knewstuff.core: Could not find category "Cantor (Qalculate)" invalid kns backend! "/etc/xdg/cantor_python3.knsrc" because: "All categories are missing" org.kde.plasma.libdiscover: Discarding invalid backend "cantor_python3.knsrc" kns error "/etc/xdg/cantor_python3.knsrc" "Invalid Cantor_python3 backend, contact your distributor." org.kde.knewstuff.core: Could not find category "Cantor (Python 3)" org.kde.knewstuff.core: Could not find category "Cantor (KAlgebra)" org.kde.knewstuff.core: Could not find category "Cantor (Python 2)" org.kde.knewstuff.core: Could not find category "Cantor (Scilab)" org.kde.knewstuff.core: Could not find category "Cantor (Octave)" org.kde.knewstuff.core: Could not find category "Cantor (Sage)" org.kde.knewstuff.core: Could not find category "Cantor (Maxima)" org.kde.knewstuff.core: Could not find category "Cantor (R)" org.kde.knewstuff.core: Could not find category "Cantor (Lua)" org.kde.knewstuff.core: Could not find category "Cantor (Qalculate)" invalid kns backend! "/etc/xdg/cantor_python2.knsrc" because: "All categories are missing" org.kde.plasma.libdiscover: Discarding invalid backend "cantor_python2.knsrc" kns error "/etc/xdg/cantor_python2.knsrc" "Invalid Cantor_python2 backend, contact your distributor." org.kde.knewstuff.core: Could not find category "Cantor (Python 3)" org.kde.knewstuff.core: Could not find category "Cantor (KAlgebra)" org.kde.knewstuff.core: Could not find category "Cantor (Python 2)" org.kde.knewstuff.core: Could not find category "Cantor (Scilab)" org.kde.knewstuff.core: Could not find category "Cantor (Octave)" org.kde.knewstuff.core: Could not find category "Cantor (Sage)" org.kde.knewstuff.core: Could not find category "Cantor (Maxima)" org.kde.knewstuff.core: Could not find category "Cantor (R)" org.kde.knewstuff.core: Could not find category "Cantor (Lua)" org.kde.knewstuff.core: Could not find category "Cantor (Qalculate)" invalid kns backend! "/etc/xdg/cantor_octave.knsrc" because: "All categories are missing" org.kde.plasma.libdiscover: Discarding invalid backend "cantor_octave.knsrc" kns error "/etc/xdg/cantor_octave.knsrc" "Invalid Cantor_octave backend, contact your distributor." org.kde.knewstuff.core: Could not find category "Cantor (Python 3)" org.kde.knewstuff.core: Could not find category "Cantor (KAlgebra)" org.kde.knewstuff.core: Could not find category "Cantor (Python 2)" org.kde.knewstuff.core: Could not find category "Cantor (Scilab)" org.kde.knewstuff.core: Could not find category "Cantor (Octave)" org.kde.knewstuff.core: Could not find category "Cantor (Sage)" org.kde.knewstuff.core: Could not find category "Cantor (Maxima)" org.kde.knewstuff.core: Could not find category "Cantor (R)" org.kde.knewstuff.core: Could not find category "Cantor (Lua)" org.kde.knewstuff.core: Could not find category "Cantor (Qalculate)" invalid kns backend! "/etc/xdg/cantor_r.knsrc" because: "All categories are missing" org.kde.plasma.libdiscover: Discarding invalid backend "cantor_r.knsrc" kns error "/etc/xdg/cantor_r.knsrc" "Invalid Cantor_r backend, contact your distributor." org.kde.knewstuff.core: Could not find category "Parley" org.kde.knewstuff.core: "Socket operation timed out" kns error "/etc/xdg/kalzium.knsrc" "Loading of providers from file: http://data.kstuff.org/cgi-bin/hotstuff-provider?site=kalzium failed" qml: message: kalzium.knsrc: Loading of providers from file: http://data.kstuff.org/cgi-bin/hotstuff-provider?site=kalzium failed PackageKit stopped running! EXPECTED RESULT Normal startup of discover. Memory consumption is maybe a bug in appstream/discover. SOFTWARE VERSIONS (available in About System) KDE Plasma Version: 5.14.2 KDE Frameworks Version: 5.51.0 Qt Version: 5.11.2 Using Arch packages: cantor 18.08.2-1 appstream-0.12.3-1 discover-5.14.2-1 ADDITIONAL INFORMATION When cantor is not installed opening discover works fine.
I can't reproduce it. On my Ubuntu 18.04 and Kde Neon Useredition-20180920 (in VirtualBox) the presence or absence of Cantor does not affect on Discover. That about this messages about categories: in this moment we haven't any categories in kde.store. Cantor without any backends also reproduce this error?
I've just been testing this and it works fine for me. Can you reproduce the issue? The CPU/Memory consumption problem you're referring to has been solved already for 5.15. Sorry for the inconvenience.
Cantor developers tell me that these categories were just added, now it will work fine. Sorry for the inconvenience.
Sorry that I have been unresponsive, I was away until now. I will get to my Arch machine tomorrow to check it out. Thanks for the quick fix!
Now with cantor 18.08.3-1 appstream 0.12.3-1 discover 5.14.3-1 on KDE 5.14.3 all problems have gone away! Thanks again.