# Docker Registries

**Registries** store and distribute images. Docker Hub is the public default registry; you pull images from it without specifying a registry hostname. Push with `docker push` and pull with `docker pull`. Private registries require authentication via `docker login`.

```bash
$ docker pull ubuntu               # pull from Docker Hub (default)
$ docker push myrepo/myapp:1.0     # push to Docker Hub
$ docker login myregistry.com      # authenticate to a private registry
$ docker pull myregistry.com/myapp # pull from private registry
$ docker logout                    # logout from a registry
```

A registry URL follows the format `<hostname>/<namespace>/<repository>:<tag>`. Images must be tagged with the registry hostname before pushing to a private registry. Docker Hub images can omit the hostname (e.g., `ubuntu:latest` is shorthand for `docker.io/library/ubuntu:latest`). Private registries require valid credentials stored locally after `docker login`.