Docker ps and other subcommands hang everywhere on CentOS 7.2

Question

In a CentOS7.2 window with Docker 1.10.3, I have successfully configured a simple docker image that can be launched at boot time using systemd. The container works fine and does what it should do (it just starts apache to serve some content on the displayed volume).

Which is strange, if I write to the window where it works, sudo to root, and then run " docker anysubcommandbutversion" (" ps", " info", etc.), it just sits there and forever, until I bought it.

I can see from https://github.com/docker/docker/issues/12606 that this might be a FAQ, but I have not seen a clear solution.