TL;DR: The client cannot talk to the Docker daemon: it is not running, or you lack permission to reach the socket. Start the daemon (or Docker Desktop) and make sure your user can read the socket.

```text
docker.errors.DockerException: Error while fetching server API version: ('Connection aborted.', FileNotFoundError(2, 'No such file or directory'))
```

## Fix it

1. Check the daemon: docker version. Expected: both Client and Server sections. If Server errors, the daemon is down.
2. Start it: systemctl start docker on Linux, or launch Docker Desktop on Mac/Windows. Expected: docker version shows the server.
3. If the daemon runs but you get permission denied, add your user to the docker group and re-login: sudo usermod -aG docker $USER. Expected: docker ps works without sudo.
4. If you use a remote daemon, set DOCKER_HOST to the right tcp or ssh URL. Expected: the client connects.

## When this applies
- Any docker-py call fails with Error while fetching server API version.

## When it doesn't
- docker version works in the shell but Python fails: check DOCKER_HOST env in the Python process.
- The error is APIError 400/404: the daemon is reachable; the request is bad.

## Compatibility
- docker-py any version; daemon any recent.

## Why it happens
docker-py probes the daemon's /version endpoint on first use. No daemon, no socket, or no permission all surface as this one error.

## Edge cases
- In CI, use the docker:dind service or mount the host socket; a bare python image has no daemon.
- Snap-installed docker uses a different socket path; set DOCKER_HOST accordingly.