"ImportError: cannot import name OVSLegacyKernelSwitch"

My VirtualMachine OS is Ubuntu14.04, Linux. Recently I want to install the mininet in my OS, and I used the following steps to install it:

cd mininet
util/install.sh -a

then it successfully. However, when I tried the command mn to start mininet, I got this exception:

root@ubuntu:/home/wasdns# mn
Traceback (most recent call last):
  File "/usr/bin/mn", line 27, in <module>
    from mininet.node import ( Host, CPULimitedHost, Controller, OVSController,
ImportError: cannot import name OVSLegacyKernelSwitch

The way I solved it is adding sudo to the command: sudo mn.

2017/1/18