Cannot get to $rootScope

I don't suggest you to use syntax like you did. AngularJs lets you to have different functionalities as you want (run, config, service, factory, etc..), which are more professional.In this function you don't even have to inject that by yourself like

MainCtrl.$inject = ['$scope', '$rootScope', '$location', 'socket', ...];

you can use it, as you know.

You can not ask for instance during configuration phase - you can ask only for providers.

var app = angular.module('modx', []);

// configure stuff
app.config(function($routeProvider, $locationProvider) {
  // you can inject any provider here
});

// run blocks
app.run(function($rootScope) {
  // you can inject any instance here
});

See http://docs.angularjs.org/guide/module for more info.

I've found the following "pattern" to be very useful:

MainCtrl.$inject = ['$scope', '$rootScope', '$location', 'socket', ...];
function MainCtrl (scope, rootscope, location, thesocket, ...) {

where, MainCtrl is a controller. I am uncomfortable relying on the parameter names of the Controller function doing a one-for-one mimic of the instances for fear that I might change names and muck things up. I much prefer explicitly using $inject for this purpose.