On Linux Mint 17.1 x86_64 with kernel 3.13.0-48-generic and OpenSSL version 1.0.1f-1ubuntu2.11; whenever I try to execute any docker command (like docker login
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Ran into the same problem after following the steps at https://docs.docker.com/linux/step_one/. docker service was running and I had also added the user to docker group. docker commands were not working without sudo.
What solved it for me was restarting the PC. Note- Before PC restart, I had also tried stopping and starting the docker daemon. I'm on Ubuntu 12.04.