Confirmed on this system. /usr/share/fonts/truetype/katex/ had 60 files
from fonts-katex (pulled in via kubuntu-desktop → neochat →
libquotientqt6-0.9 → libolm3 Recommends → libjs-katex → fonts-katex, all
automatic, never installed manually).
With the system cache (/var/cache/fontconfig, no user overrides):
$ fc-match -v sans | grep -E 'file|fontversion'
file: "/usr/share/fonts/truetype/katex/KaTeX_AMS-Regular.woff"(s)
fontversion: 2147483647(i)(s)
This matches the report exactly.
Fix applied:
sudo apt purge fonts-katex libjs-katex
sudo rm -rf /var/cache/fontconfig/*
rm -rf ~/.cache/fontconfig
sudo fc-cache -f && fc-cache -f
After this, fc-match sans returns NotoSans-Regular.ttf. A minimal PyQt6
reproducer (single QPushButton labeled U+25B6) that previously crashed
6/6 with SIGSEGV in FcCharSetHasChar (same stack as reported:
QFontEngineMultiFontConfig::shouldLoadFontEngineForCharacter ->
QFontEngineMulti::stringToCMap -> QTextEngine::shapeText) now passes 6/6
(rc 0) with no FONTCONFIG_* overrides. No crashes in plasmashell,
konsole, kate in several hours since, versus the previous pattern of
crashes within seconds.
Removing fonts-katex/libjs-katex did not remove any other package on this
system (verified with apt-get install -s fonts-katex- libjs-katex- beforehand).
Worth noting for others hitting this via the same dependency chain
(neochat/libolm3 Recommends) that the packages are safe to purge without
breaking neochat.
(Analysed with the help of an AI assistant, Claude.)
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https://bugs.launchpad.net/bugs/2168420
Title:
libfontconfig: SIGSEGV in FcCharSetHasChar (rax=0xfefefefefefefefe)
in Qt6 apps with a user font cache in ~/.cache/fontconfig
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