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docker-mailserver/docs/content/config/advanced/maintenance/update-and-cleanup.md
Brennan Kinney 4a58e2eb83
docs: Revise watchtower page (#3583) 
- Better clarify images are only updated to newer image updates to the same tag of the running container(s).
- Slight revisions to existing content.
2023-10-16 15:20:50 +02:00

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title
Maintenance | Update and Cleanup

containrrr/watchtower is a service that monitors Docker images for updates, automatically applying them to running containers.

!!! example "Automatic image updates + cleanup"

Run a `watchtower` container with access to `docker.sock`, enabling the service to manage Docker:

```yaml title="compose.yaml"
services:
  watchtower:
    image: containrrr/watchtower:latest
    # Automatic cleanup (removes older image pulls from wasting disk space):
    environment:
      - WATCHTOWER_CLEANUP=true
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock
```

!!! tip "The image tag used for a container is monitored for updates (eg: :latest, :edge, :13)"

The automatic update support is **only for updates to that specific image tag**.

- Your container will not update to a new major version tag (_unless using `:latest`_).
- Omit the minor or patch portion of the semver tag to receive updates for the omitted portion (_eg: `13` will represent the latest minor + patch release of `v13`_).

!!! tip "Updating only specific containers"

By default the `watchtower` service will check every 24 hours for new image updates to pull, based on currently running containers (_**not restricted** to only those running within your `compose.yaml`_).

Images eligible for updates can configured with a [custom `command`][docker-docs-compose-command] that provides a list of container names, or via other supported options (eg: labels). This configuration is detailed in the [`watchtower` docs][watchtower-docs].

!!! info "Manual cleanup"

`watchtower` also supports running on-demand with `docker run` or `compose.yaml` via the `--run-once` option.

You can alternatively invoke cleanup of Docker storage directly with:

- [`docker image prune --all`][docker-docs-prune-image]
- [`docker system prune --all`][docker-docs-prune-system] (_also removes unused containers, networks, build cache_).

If you omit the `--all` option, this will instead only remove ["dangling" content][docker-prune-dangling] (_eg: Orphaned images_).