Tip: Can't find docker networking namespace via ip netns list

Symptom:

    In ubuntu, we start a docker container, try to find docker networking namespace via "ip netns list". The output is empty.

Reason:

   The docker by default , it records netns on /var/run/docker/netns. While "ip netns list" is checking /var/run/netns

Workaround:  

 stop all containers , rm -rf /var/run/netns,  ln -s /var/run/docker/netns  /var/run/netns

Tip:

To find netns id of container use

docker ps ---> find container ID

docker inspect <contain ID> |grep netns