# Running the dita command from a Docker image

Docker is a platform used to build, share, and run portable application containers. As of version 3.4, the DITA-OT project provides an official Docker container image that includes everything you need to run the toolkit and publish DITA content from a containerized environment.

## About application containers

Using containers to deploy applications isolates software from its environment to ensure that it works consistently despite any differences in the host operating system, for example.

Docker containers are designed as stateless machines that can be quickly created and destroyed, started and stopped. Each Docker image provides its own private filesystem that includes only the code required to run the application itself — it is not intended for persistent data storage.

When a container is stopped, any changes made within the container are lost, so source files and generated output should be stored outside the container. These resources are attached to the container by mounting directories from the host machine.

Important:
If you use Podman to manage and run your containers, you must substitute `podman --userns=keep-id:uid=UID,gid=GID` for the docker command in the instructions below. For DITA-OT versions 4.2.3 and earlier, both UID and GID are `1000`. For all later DITA-OT versions, both values are `1001`.

## Before you begin

To run the DITA-OT image, you will need to install Docker and be able to access the GitHub Container Registry.

- To download Docker Desktop, you may be prompted to sign in with your Docker ID (or sign up to create one).

## Procedure

1. Install Docker for your operating system.
   - Install Docker Desktop on Windows
   - Install Docker Desktop on Mac
   - On macOS, you can also install Docker Desktop via Homebrew:

         $ brew install homebrew/cask/docker
         Downloading…

   - When you first run the Docker Desktop application, you may be prompted to grant privileged access to allow Docker to install its networking components and links to the Docker apps. Grant this access and accept the service agreement to proceed.
   - On Linux, install Docker Community Edition (CE) via your operating system’s package manager, for example:

         $ sudo apt-get install docker-ce

2. To build output, map a host directory to a container volume and specify options for the dita command.

       $ docker run --rm \
         -v /Users/username/source:/src ghcr.io/dita-ot/dita-ot:4.4.1 \
         -i /src/input.ditamap \
         -o /src/out \
         -f html5 -v

   This command sequence specifies the following options:
   - -v mounts the source subfolder of your home directory and binds it to the /src volume in the container
   - -i specifies the input.ditamap file in your source folder as the input map file
   - -o writes the output to source/out
   - -f sets the output format to HTML5, and
   - -v displays build progress messages with verbose logging

   On Windows, if your Users directory is on the C:\ drive, use /c/Users/… to map the host directory:

       > C:\Users\username> docker run --rm ^
         -v /c/Users/username/source:/src ghcr.io/dita-ot/dita-ot:4.4.1 ^
         -i /src/input.ditamap ^
         -o /src/out ^
         -f html5 -v

   Note:
   The DITA-OT container image uses the `ENTRYPOINT` instruction to run the dita command from the /opt/app/bin/ directory of the container automatically, so you there’s no need to include the dita command itself, only the arguments and options you need to publish your content.