GitLab CI Docker Daemon Not Running

What is GitLab CI Docker Daemon Not Running

Understanding GitLab CI

GitLab CI/CD is a powerful tool integrated into GitLab that allows developers to automate the process of software development, testing, and deployment. It uses pipelines, which are defined in a .gitlab-ci.yml file, to execute jobs in a specified order. These jobs can be run on different types of runners, including those that require Docker.

Identifying the Symptom

When using GitLab CI, you might encounter an error indicating that the Docker daemon is not running. This typically manifests as a job failure with error messages such as:

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

This error suggests that the job requires Docker to be operational, but the Docker service is not active on the runner machine.

Exploring the Issue

The error occurs because the Docker daemon, which is a background service responsible for managing Docker containers, is not running. This is crucial for any CI job that involves building, running, or interacting with Docker containers. Without the daemon, Docker commands cannot be executed, leading to job failures.

Why Docker is Essential

Docker is widely used in CI/CD pipelines for its ability to create isolated environments, ensuring consistency across different stages of development and deployment. Learn more about Docker's role in CI/CD here.

Steps to Resolve the Issue

To resolve the issue of the Docker daemon not running, follow these steps:

Step 1: Verify Docker Installation

Ensure that Docker is installed on your runner. You can check this by running:

docker --version

If Docker is not installed, follow the official Docker installation guide.

Step 2: Start the Docker Daemon

To start the Docker daemon, use the following command:

sudo systemctl start docker

To ensure Docker starts automatically at boot, enable it with:

sudo systemctl enable docker

Step 3: Verify Docker Daemon Status

Check if the Docker daemon is running with:

sudo systemctl status docker

The output should indicate that the service is active and running.

Conclusion

By ensuring the Docker daemon is running, you can resolve the issue and allow your GitLab CI jobs to execute successfully. For more detailed troubleshooting, refer to the GitLab Runner Docker Executor documentation.