Problem
Since upgrading to Debian 13, my wife's Cinnamon 6.4.10 desktop always showed an error in the Nemo file manager (6.4.5):
Ein Problem wurde mit Ihrem Vorschaubildpuffer festgestellt.
Das zu reparieren benötigt Systemverwaltungsrechte
Jetzt reparieren
Verwerfen
A problem has been detected with your thumbnail cache.
Fixing it will require administrative privileges.
Fix now
Dismiss
I'm writing this blog post because the "Fix now" button did not work.
No thumbnails were shown at all, not even for old files.
Solution
Manually deleting the thumbnail directory:
$ rm -rf ~/.cache/thumbnails
After doing that and starting Nemo, the preview images were shown again - even after multiple Nemo restarts.
Notes
Related nemo bug report #3447, without solution.
The debug command given there did not yield helpful output; it only added one additional line on terminal:
$ NEMO_DEBUG=Thumbnails,DirectoryView nemo --debug ~/Bilder/onlyone (nemo:10383): Nemo-WARNING **: 10:49:02.195: Current gtk theme is not known to have nemo support (Ambiance) - checking... (nemo:10383): Nemo-WARNING **: 10:49:02.217: The theme appears to have no nemo support. Adding some... (nemo:10383): Nemo-DEBUG: 10:49:02.218: Open called on the GApplication instance; 1 files
The home and cache directories are on the local disk, not NFS or so.
Nemo uses registered thumbnailers to generate the preview images. It looked into the following directories (found with strace nemo):
~/.local/share/thumbnailers /usr/share/gnome/thumbnailers ~/.local/share/flatpak/exports/share/thumbnailers /var/lib/flatpak/exports/share/thumbnailers /usr/local/share/thumbnailers /usr/share/thumbnailers