had to set an explicit -socket path- in cluster.js to work on dev VM, set to /tmp

cluster.js

@@ -26,6 +26,8 @@ var env          = require(__dirname + '/config/environments/' + ENV)
 _.extend(global.settings, env);
  
 cluster('./app/controllers/app')
+  .set('workers', 2)
+  .set('socket path', '/tmp')
   .use(cluster.logger('logs'))
   .use(cluster.stats())
   .use(cluster.pidfiles('pids'))

package.json

@@ -4,7 +4,7 @@
   "description": "high speed SQL api for cartodb",
   "version": "0.0.1",
   "dependencies": {
-		"cluster": "0.6.4",
+		"cluster": "0.6.9",
     "express": "2.4.3",
 		"underscore"  : "1.1.x",
 		"underscore.string": "1.1.5",