Run docker as non-root user (without sudo)

Run Docker as non-root user (without sudo)in ubuntu/linux

To fix the Docker permission denied error and use Docker as non-root user, 
(like Got permission denied while trying to connect to the Docker daemon socket at...connect: permission denied)
create a group called “docker” with the following command:

$ sudo groupadd docker

Next, add your user to the docker group:
$ sudo usermod -aG docker $USER

After adding the user to the docker group, log out and log back in to take effect the changes.

Alternatively, run the following command to apply the changes to groups:
$ newgrp docker

From now on, the normal (non-root) user can be able to use Docker without sudo permissions.
$ docker version