def link(self,rel):
        for link in self.ln:
            if ('rel' in link and
                link['rel']==rel):
                return(link)
        return(None)
``DockerBuildScript.main`` calls ``run`` on the instance returned by
dataset/ETHPy150Open resync/resync/resync/resource_container.py/ResourceContainer.link--crossover with--dataset/ETHPy150Open ClusterHQ/flocker/admin/test/test_packaging.py/DockerBuildScriptTests.test_run