Linux tip: refresh your fontconfig cache regularly, or calibre may segfault

[spiritomb]

I had a strange problem with my Calibre setup on Linux that began a few days ago and I just figured out the solution, after a lot of troubleshooting.

My system setup:
calibre 9.9.0 installed the recommended way, to /opt, not via system repo or AUR
Arch Linux (rolling)
desktop environment: i3

The problem: Calibre would segfault whenever I clicked the Edit Metadata button or clicked the message in the lower-right corner that opens the plugin-updater window. Running

calibre-debug -g

in a terminal showed the program starting fine. The only error I received in the terminal was

segmentation fault (core dumped)  calibre

, immediately upon clicking Edit Metadata or attempting to open the plugin updater window.

Things I tried (list not necessarily in order):

• disabling all 3rd-party plugins (the segfault still happened)
• uninstalling unneeded system python libraries (I thought there was a conflict with C
  calibre's somehow even though I was not using a system repo version; this changed nothing)
• uninstalling calibre 9.9.0 and installing an earlier version (did not solve the problem)
• renaming ~/.cache/calibre and ~/.config/calibre to see if the problem persisted with a completely new library and no third-party plugins (it did)

What actually fixed the problem? Forcibly rebuilding my system's fontconfig cache by opening a terminal and running

fc-cache -f

.

I'm sharing this information here in case any other Linux user encounters this odd problem, because the only reason I figured it out was because a different program (conky) wasn't detecting my installed fonts like it should have been.