- Jan 2017
Cannot connect to the Docker daemon
For Linux/Unix people, it may very well be that you did not add your username to the 'docker' group and as a consequence you cannot communicate with the docker daemon. I had just experienced this (while running Linux Mint 18.1, but the symptoms ought to be similar for Debian/Ubuntu as well).
To fix it, I ran:
sudo usermod -aG docker $(whoami)
Log out and log back in. This ensures your user is running with the correct permissions.
This will ensure that you do not need to sudo every time, when you interact with docker.
There are instructions in the below link for Unix (MacOS) users as well.