Watchtower is itself packaged as a Docker container so installation is as simple as pulling the `containrrr/watchtower` image. If you are using ARM based architecture, pull the appropriate `containrrr/watchtower:armhf-<tag>` image from the [containrrr Docker Hub](https://hub.docker.com/r/containrrr/watchtower/tags/).
Since the watchtower code needs to interact with the Docker API in order to monitor the running containers, you need to mount _/var/run/docker.sock_ into the container with the `-v` flag when you run it.
Run the `watchtower` container with the following command:
```bash
docker run -d \
--name watchtower \
-v /var/run/docker.sock:/var/run/docker.sock \
containrrr/watchtower
```
If pulling images from private Docker registries, supply registry authentication credentials with the environment variables `REPO_USER` and `REPO_PASS`
or by mounting the host's docker config file into the container (at the root of the container filesystem `/`).
Passing environment variables:
```bash
docker run -d \
--name watchtower \
-e REPO_USER=username \
-e REPO_PASS=password \
-v /var/run/docker.sock:/var/run/docker.sock \
containrrr/watchtower container_to_watch --debug
```
Also check out [this Stack Overflow answer](https://stackoverflow.com/a/30494145/7872793) for more options on how to pass environment variables.
If you mount the config file as described above, be sure to also prepend the URL for the registry when starting up your watched image (you can omit the https://). Here is a complete docker-compose.yml file that starts up a docker container from a private repo at Docker Hub and monitors it with watchtower. Note the command argument changing the interval to 30s rather than the default 5 minutes.
