The broker config.xml file which is shipped in the etc directory of any Qpid binary distribution details various options and configuration for the Java Qpid broker implementation.
In tandem with the virtualhosts.xml file, the config.xml file allows you to control much of the deployment detail for your Qpid broker in a flexible fashion.
Note that you can pass the config.xml you wish to use for your broker instance to the broker using the -c command line option. In turn, you can specify the paths for the broker password file and virtualhosts.xml files in your config.xml for simplicity.
For more information about command line configuration options please see ???.