# Installing KumoMTA in a Docker container


To build a lightweight alpine-based docker image:

- Prepare your system with the needed essentials (see[ System Preparation](./system_preparation.md))
- Ensure docker is actually installed in your server instance.

=== "DNF based systems"
    In Rocky, Alma, and any other DNF package manager system

    ```bash
    sudo dnf config-manager --add-repo=https://download.docker.com/linux/centos/docker-ce.repo
    sudo dnf update -y
    sudo dnf install -y docker-ce docker-ce-cli containerd.io
    sudo systemctl enable docker
    ```

=== "APT based systems"

    In Ubuntu, Debian, and other Debial APT package management systems:

    ```bash
    sudo apt update
    sudo apt install -y apt-utils docker.io
    sudo snap install docker
    ```



If you get an error that `/etc/rc.d/rc.local is not marked executable` then make it executable with `sudo chmod +x /etc/rc.d/rc.local`

### Start Docker

```bash
$ sudo systemctl start docker
```

### Check if Docker is running

```bash
$ systemctl status docker
```

### Enable Non-Root User Access

After completing Step 3, you can use Docker by prepending each command with sudo. To eliminate the need for administrative access authorization, set up a non-root user access by following the steps below.

1. Use the usermod command to add the user to the docker system group.
  ```baseh
  $ sudo usermod -aG docker $USER
  ```

2. Confirm the user is a member of the docker group by typing:
  ```bash
  $ id $USER
  ```

It is a good idea to restart to make sure it is all set correctly (init 6)

### Build the docker image

At the time of this writing, the Docker image needs to be built from the project repo.  You will need to clone the repo and then build the image from `./docker`.

```bash
$ sudo dnf install -y git
$ git clone https://github.com/kumomta/kumomta.git

$ cd kumomta/docker/redis/
$ sudo docker build -t redis-cell .
$ docker run --name redis -p 6379:6379 -d redis-cell
$ cd ../..
$ sudo ./docker/kumod/build-docker-image.sh
```

This should result in something roughly like this:

```bash
$ docker image ls kumomta/kumod
REPOSITORY      TAG       IMAGE ID       CREATED         SIZE
kumomta/kumod   latest    bbced15ff4d1   3 minutes ago   116MB
```

You can then run that image; this invocation mounts the kumo src dir at `/config` and then the `KUMO_POLICY` environment
variable is used to override the default `/config/policy.lua` path to use the SMTP sink policy script [sink.lua](https://github.com/kumomta/kumomta/blob/main/sink.lua), which will accept and discard all mail:

```bash
$ sudo docker run --rm -p 2025:25 \
    -v .:/config \
    --name kumo-sink \
    --env KUMO_POLICY="/config/sink.lua" \
    kumomta/kumod
```