Building your first Docker image

Docker images are the basic way of sharing software in bioboxes. This guide describes creating a Docker image. This includes using Dockerfiles and the commands used to create and name the images made from Dockerfiles.


The first step to creating an image of your tool is to write a file called Dockerfile. Each line in a Dockerfile is a set of instructions that are to build an image. Here's the most simple Dockerfile you can have. Begin by creating your own Dockerfile with these contents.

FROM busybox

Each line in the file must begin with a recognised Dockerfile command. In this case the commands are FROM and MAINTAINER. The first described a base Docker image that we'll build our own on top of. Here we use the 'busybox' image. This is the same image we experimented with in the user guide. On the second line we specify the name and email address person who is responsible for this image. Once you've created this image you can build it with the command:

You can test this example Dockerfile by building it into an image using docker build. The --tag specifies what the image should be called. In this case we'll call the image "my_image". Run the following command in the same directory you have placed your Dockerfile.

docker build --tag my_image .

If this builds successfully you should have a Docker image called 'my_image' Docker image available on your system. You list all your images with the command.

docker images

Running a container

When you're building a container it's useful to be able to log into it so you can experiment. You can create a container from this image and log in using the --interactive and --tty flags. You should specify a shell command to run also, in this case we use /bin/bash which is the command to start the bash shell. If you're not too familiar with what bash is, it's fine to use this command, without understanding the details, whenever you want to log into a container.

docker run --interactive --tty my_image /bin/bash

Once you've logged into a container you can experiment with listing the internal file system or the current version of Linux.


The output of both these commands comes from the operating system inside the container, not your host computer. If this is not clear, there is a guide we explaining the difference between containers and images. You can exit this container with CTRL+D.

An image to do something

You will want to create an image to do something useful that you can share with others. We'll create an example Docker that returns the current time when run.

FROM busybox


This uses the ENTRYPOINT directive to specify this command gets run when the container gets run. In this case we specify the date should be run. Build and run this container, and you should see your image tells you the current date and time.

docker build --tag timepiece .
docker run timepiece

You can specify different date output formats by passing these as an argument to the docker run command. For example you can pass a format string and the date will be returned in this format.

docker run timepiece +"%Y-%m-%d"