GitLab CI "Cannot connect to the Docker daemon" (dind)

By Kaveh Alemi·Latchkey

Your job ran a docker command but there is no daemon to talk to. In GitLab CI you must attach a Docker-in-Docker service and point the client at it.

What this error means

A docker build/docker push step fails immediately: "Cannot connect to the Docker daemon ... Is the docker daemon running?" The rest of the job is fine - only Docker has nowhere to connect.

Cannot connect to the Docker daemon at unix:///var/run/docker.sock.
Is the docker daemon running?

Common causes

No dind service attached

The Docker executor does not give jobs a daemon by default. Without a docker:dind service, there is no daemon for the client to reach.

DOCKER_HOST / TLS not configured

With dind over TLS, the client needs DOCKER_HOST, DOCKER_TLS_CERTDIR, and the cert path set. Missing or mismatched values leave the client pointed at a non-existent socket.

How to fix it

Attach docker:dind and set the host

build:
  image: docker:27
  services:
    - docker:27-dind
  variables:
    DOCKER_HOST: tcp://docker:2376
    DOCKER_TLS_CERTDIR: "/certs"
    DOCKER_CERT_PATH: "/certs/client"
    DOCKER_TLS_VERIFY: "1"
  script:
    - docker build -t myimage .

Or use the host socket deliberately

If your runner is configured to mount /var/run/docker.sock, you do not need dind - but this shares the host daemon and is a security trade-off.

How to prevent it

• Standardize a dind template (services, DOCKER_HOST, TLS) and extends it.
• Pin matching docker and docker:dind versions.
• Avoid socket-binding on shared runners for security.

Frequently asked questions

Related guides

References

• Docker documentation
• Docker build cache
• GitHub Actions documentation