Docker: permission denied while trying to connect to Docker Daemon with local CircleCI build

I've created a workaround for myself.

In the very first step of the config.yml, I run this command:

if [[ $CIRCLE_SHELL_ENV == *"localbuild"* ]]; then
  echo "This is a local build. Enabling sudo for docker"
  echo sudo > ~/sudo
else
  echo "This is not a local build. Disabling sudo for docker"
  touch ~/sudo
fi

Afterwards, you can do this:

eval `cat ~/sudo` docker build .

Explanation:

The first snippet checks if the CircleCI-provided environment variable CIRCLE_SHELL_ENV contains localbuild. This is only true when running circleci build on your local machine. If true, it creates a file called sudo with contents sudo in the home directory. If false, it creates a file called sudo with NO contents in the home directory.

The second snippet opens the ~/sudo file, and executes it with the arguments you give afterwards. If the ~/sudo file contains "sudo", the command in this example will become sudo docker build ., if it doesn't contain anything, it will become docker build ., with a space before it, but that will be ignored.

This way, both the local (circleci build) builds and remote builds will work.

To iterate on the answer of Jeff Huijsmans,

an alternative version is to use a Bash variable for docker:

- run:
    name: Set up docker
    command: |
        if [[ $CIRCLE_SHELL_ENV == *"localbuild"* ]]; then
            echo "export docker='sudo docker'" >> $BASH_ENV
        else
            echo "export docker='docker'" >> $BASH_ENV
        fi

Then you can use it in your config

- run:
    name: Verify docker
    command: $docker --version

You can see this in action in my test for my Dotfiles repository

Documentation about environment variables in CircleCi