# S6 overlay

> The init system in the Home Assistant base images. It starts, watches, and stops the programs of an app inside its container.

Source: https://contributors.home-assistant.io/glossary/s6-overlay/

- In code: `/init`, `/etc/s6-overlay/s6-rc.d/`
- Also: s6-overlay, S6

Docker runs one command per container. [S6 overlay](https://github.com/just-containers/s6-overlay) lets an app run several, in the right order: a setup step first, then the programs, restarted when they crash. The base images make its `/init` the entrypoint, so an app only adds its service definitions. See [Run services with S6 overlay](https://contributors.home-assistant.io/apps/guides/s6-overlay/).

## Related terms

- [App](https://contributors.home-assistant.io/glossary/app/): Extra software that runs next to Home Assistant on Home Assistant OS, like an MQTT broker or a file editor.
- [Bashio](https://contributors.home-assistant.io/glossary/bashio/): A library of Bash functions for apps, with helpers for reading the app's options, logging, and talking to the Supervisor API.