Linux – How to resolve the error "can't connect to Docker daemon

The "can't connect to Docker daemon" error is one of the most common issues that new Docker users encounter when trying to start Docker services. This error typically appears when attempting to run Docker commands like docker-compose build or other Docker operations.

The docker-compose command is a tool used for defining and running multi-container Docker applications. When the Docker daemon is not properly running or accessible, you'll see an error message like this:

Cannot connect to the Docker daemon. Is the docker daemon running on this host?

Common Causes

This error occurs due to several reasons:

• Docker daemon service is not running

• Current user lacks permission to access Docker

• Docker socket file has incorrect permissions

• Post-installation steps were not completed properly

Solutions for Ubuntu/Fedora

Step 1: Create Docker Group

First, create the docker group using the following command:

sudo groupadd docker

Step 2: Add User to Docker Group

Add your current user to the docker group to grant necessary permissions:

sudo usermod -aG docker $USER

Replace $USER with your actual username if needed, or use $(whoami) to automatically use the current user.

Step 3: Apply Group Changes

Log out and log back in to ensure the group membership changes take effect, or run:

newgrp docker

Step 4: Start Docker Service

Start the Docker daemon service:

sudo systemctl start docker
sudo systemctl enable docker

Solutions for macOS

Using Docker Desktop

For modern macOS installations with Docker Desktop, simply start the Docker Desktop application from your Applications folder.

Using Docker Machine (Legacy)

If using Docker Machine, start the virtual machine:

docker-machine start

Get the environment variables:

docker-machine env

Configure your shell to use the Docker environment:

eval $(docker-machine env)

Verification

Test if Docker is working correctly by running:

docker run hello-world

If successful, you should see a welcome message confirming Docker is properly configured.

Conclusion

The Docker daemon connection error is typically resolved by ensuring proper user permissions and starting the Docker service correctly. Following the post-installation steps and adding your user to the docker group eliminates most permission-related issues and allows seamless Docker operations.