pycharm remote debugging: failed to find free socket

问题

I'm trying to use remote debugging but get this error on pycharm:

Error running remoteTest: failed to find free socket

My remote host is Ubuntu |(with username and password) and my localhost is windows, I followed the following tutorial: https://blog.jetbrains.com/pycharm/2010/12/python-remote-debug-with-pycharm/ and I used a ssh tunnel on putty to connect to the server.

import pydevd
pydevd.settrace('localhost', port=21000, stdoutToServer=True, stderrToServer=True)

来源：https://stackoverflow.com/questions/42678246/pycharm-remote-debugging-failed-to-find-free-socket