diff --git a/ruby/trema/open-vswitch.rb b/ruby/trema/open-vswitch.rb
index 37341e0..ed0a2ca 100644
--- a/ruby/trema/open-vswitch.rb
+++ b/ruby/trema/open-vswitch.rb
@@ -195,6 +195,7 @@ module Trema
        "--verbose=ANY:console:err",
        "--log-file=#{ log_file }",
        "--datapath-id=#{ dpid_long }",
+       "--unixctl=#{ unixctl }",
       ] + ports_option
     end

@@ -233,6 +234,18 @@ module Trema
     def log_file
       "#{ Trema.tmp }/log/openflowd.#{ @name }.log"
     end
+
+
+    #
+    # The path of control socket
+    #
+    # @return [String]
+    #
+    # @api private
+    #
+    def unixctl
+      "#{ Trema.tmp }/ovs-openflowd.#{ $$ }.ctl"
+    end
   end
 end