nfdump -C -> config file syntax

[jniggemann]

Using 1.7.1, I see nfdump has an option -C <file> "read optional config file". I'd like to set the data directory in there and tried with cache_dir=/var/cache/nfdump, but get Failed to parse config file nfdump.conf: line 1: extra chars after value.
What options can I set there and what's the correct syntax?

[phaag]

The optional config file does not include all options, which are available on the command line. The list file nfdump.conf.dist contains all available options as comments with their default value.