act "Cannot connect to the Docker daemon" running Actions locally

By Kaveh Alemi·Latchkey

act executes each job inside a container, so it talks to a container runtime over the Docker socket. This error means no daemon is listening at /var/run/docker.sock: Docker is not started, or the socket path is wrong.

What this error means

act exits immediately with "Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?" before any job step runs.

Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?
Error: failed to start container: Error response from daemon

Common causes

No container runtime is running

Docker Desktop, dockerd, Colima, or Podman is not started, so the socket act connects to does not exist.

act points at the wrong socket

On Colima, Podman, or a rootless setup the socket lives elsewhere than /var/run/docker.sock, and DOCKER_HOST is not set to it.

How to fix it

Start the container runtime first

1. Start Docker Desktop, or run dockerd, colima start, or podman machine start.
2. Confirm the daemon responds with docker info.
3. Re-run act once docker info prints without error.

docker info
act -j build

Point act at a non-default socket

For Colima or Podman, export DOCKER_HOST (or pass --container-daemon-socket) so act finds the running daemon.

export DOCKER_HOST="unix://$HOME/.colima/default/docker.sock"
act -j build

How to prevent it

• Confirm docker info succeeds before invoking act.
• Set DOCKER_HOST in your shell profile when using Colima or Podman.
• Remember act is a local Docker harness, not a native runner.

Frequently asked questions

Related guides

References

• GitHub Actions documentation
• Workflow syntax for GitHub Actions