// run dbHash using the old way
> db.runCommand( { dbHash : 'config' } )
{ "ok" : 0, "errmsg" : "need a valid database name", "code" : 28539 }
// but, thisis case, the "config" database exists and is valid
> show dbs
config         0.023GB
// run with the new way with now problem
> db.runCommand( { dbHash : 1, collections: ['config'] } )
{
	"host" : "Stevens-MacBook-Pro-2.local",
	"collections" : {
		
	},
	"md5" : "d41d8cd98f00b204e9800998ecf8427e",
	"timeMillis" : 0,
	"fromCache" : [ ],
	"ok" : 1
}