mininetエラー解決:Exception:Could not find a default OpenFlow controllerとCannot find required executable


朝mininetを使った時に次のように間違えました.
Traceback (most recent call last):
  File "simple.py", line 63, in myTest
    net=Mininet(MyTopo())
  File "/usr/lib/python2.7/dist-packages/mininet/net.py", line 172, in __init__
    self.build()
  File "/usr/lib/python2.7/dist-packages/mininet/net.py", line 442, in build
    self.buildFromTopo( self.topo )
  File "/usr/lib/python2.7/dist-packages/mininet/net.py", line 409, in buildFromTopo
    self.addController( 'c%d' % i, cls )
  File "/usr/lib/python2.7/dist-packages/mininet/net.py", line 261, in addController
    controller_new = controller( name, **params )
  File "/usr/lib/python2.7/dist-packages/mininet/node.py", line 1518, in DefaultController
    raise Exception( 'Could not find a default OpenFlow controller' )
Exception: Could not find a default OpenFlow controller

このエラーは長い間存在していますが、2つのステップで解決する必要があります.
from mininet.node import OVSController
net = Mininet(topo = topo, controller = OVSController)

注意:別のコントローラを起動したい場合は、OVSControllerをRemoteControllerに変更するだけです.
次のようにエラーが表示されます.
c0 Cannot find required executable ovs-controller.
Please make sure that it is installed and available in your $PATH:
(/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games)

次にlnを使用して解決します.
sudo apt-get install openvswitch-testcontroller
sudo ln /usr/bin/ovs-testcontroller /usr/bin/controller