Openhab2 maven build

Say I hope I can build openhab2 by maven command.
I know documentation provide a way to run/debug in Eclipse IDE.
But if to run on a board, probably Eclipse IDE is not a good choice.

Note that the project build is completely mavenized - so running "mvn install" on any repository root will nicely build all artifacts.

However, there are more than one directory for openHAB2.

My questions,
1 Which repo I should download/clone and do maven build?
2 Or I should get all of them and under same directory, then trigger the maven build process somehow?

I know the issue may be trivial.
However, can some expert give some help?

Thank you very much.