[galaxy-dev] How is the paster.py running to start Galaxy Framework ?

Hello, Galaxy developers: I'm a galaxy user and have customized a Galaxy instance locally. I'm very interested in Galaxy framework and the way it's running. I've search over the doc from readthedocs and look through some source code files. But I'm confused at first: How to run paster.py to start all process to build a Galaxy server? I've no idea why the last line of code "command.run()" can start the whole Galaxy server and thanks for someone to point it out. Thanks for your help! wangdan