<commit_before>page_title: Dockerizing Applications: A "Hello World!"
page_description: A simple "Hello World!" exercise that introduced you to Docker.
page_keywords: docker guide, docker, docker platform, virtualization framework, how to, dockerize, dockerizing apps, dockerizing applications, container, containers

# Dockerizing Applications: A "Hello World!"

*So what's this Docker thing all about?*

Docker allows you to run applications inside containers. Running an
application inside a container takes a single command: `docker run`.

## Hello World!

Let's try it now.

    $ sudo docker run ubuntu:14.04 /bin/echo 'Hello World!'
    Hello World!

And you just launched your first container!

So what just happened? Let's step through what the `docker run` command
did.

First we specified the `docker` binary and the command we wanted to
execute, `run`. The `docker run` combination *runs* containers.

Next we specified an image: `ubuntu:14.04`. This is the source of the container
we ran. Docker calls this an image. In this case we used an Ubuntu 14.04
operating system image.

When you specify an image, Docker looks first for the image on your
Docker host. If it can't find it then it downloads the image from the public
image registry: [Docker Hub](https://hub.docker.com).<commit_msg>exclaimation marks cause shell pain - simplify it away<commit_after>page_title: Dockerizing Applications: A "Hello World!"
page_description: A simple "Hello World!" exercise that introduced you to Docker.
page_keywords: docker guide, docker, docker platform, virtualization framework, how to, dockerize, dockerizing apps, dockerizing applications, container, containers

# Dockerizing Applications: A "Hello World!"

*So what's this Docker thing all about?*

Docker allows you to run applications inside containers. Running an
application inside a container takes a single command: `docker run`.

## Hello World!

Let's try it now.

    $ sudo docker run ubuntu:14.04 /bin/echo 'Hello World'
    Hello World!

And you just launched your first container!

So what just happened? Let's step through what the `docker run` command
did.

First we specified the `docker` binary and the command we wanted to
execute, `run`. The `docker run` combination *runs* containers.

Next we specified an image: `ubuntu:14.04`. This is the source of the container
we ran. Docker calls this an image. In this case we used an Ubuntu 14.04
operating system image.

When you specify an image, Docker looks first for the image on your
Docker host. If it can't find it then it downloads the image from the public
image registry: [Docker Hub](https://hub.docker.com).
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