Run this program in a single process mode for debugging purpose. Without this option, nghttpx creates at least 2 processes: master and worker processes. If this option is used, master and worker are unified into a single process. nghttpx still spawns additional process if neverbleed is used. In the single process mode, the signal handling feature is disabled.
Please see https://nghttp2.org/documentation/nghttpx.1.html#cmdoption-nghttpx--single-process.