Currently, the --help option only has output for the command line. In theory, we could have it output help for the various config files as well (currently YAML and INI).

The usage would be:

./mongod --help
./mongod --help cmdline
# Outputs command line help
./mongod --help yaml
# Outputs YAML config help which can also act as template config file
./mongod --help ini
# Outputs INI config help which can also act as template config file

The help for the config files would have comments that are the option descriptions in the code. The INI would be done manually (the generator should be simple) and the YAML parser we are using supports comment output: https://code.google.com/p/yaml-cpp/wiki/HowToEmitYAML