How do I set the cache directory for darktable-generate-cache, and when should I run it?

You can set the cache location explicitly with the `--cachedir` option: `darktable-generate-cache --core --cachedir ` Replace `` with the cache folder you want darktable to use. As for "when your computer is in idle," the available guidance suggests this is not a special automatic idle mode. It likely just means you should run the command when you are not otherwise heavily using the computer, since generating thumbnails uses system resources. There’s no indication here that it bypasses database locking or automatically runs alongside an open darktable session. In practice, treat it as a manual command-line tool and run it when the system is otherwise idle.