page_title: Share Images via Repositories
page_description: Repositories allow users to share images.
page_keywords: repo, repositories, usage, pull image, push image, image, documentation

# Share Images via Repositories

## Introduction

A *repository* is a shareable collection of tagged
[*images*](../../terms/image/#image-def) that together create the file
systems for containers. The repository’s name is a label that indicates
the provenance of the repository, i.e. who created it and where the
original copy is located.

You can find one or more repositories hosted on a *registry*. There can
be an implicit or explicit host name as part of the repository tag. The
implicit registry is located at `index.docker.io`,
the home of "top-level" repositories and the Central Index. This
registry may also include public "user" repositories.

Docker is not only a tool for creating and managing your own
[*containers*](../../terms/container/#container-def) – **Docker is also
a tool for sharing**. The Docker project provides a Central Registry to
host public repositories, namespaced by user, and a Central Index which
provides user authentication and search over all the public
repositories. You can host your own Registry too! Docker acts as a
client for these services via `docker search, pull, login`
and `push`.

## Repositories

### Local Repositories

Docker images which have been created and labeled on your local Docker
server need to be pushed to a Public or Private registry to be shared.

### Public Repositories

There are two types of public repositories: *top-level* repositories
which are controlled by the Docker team, and *user* repositories created
by individual contributors. Anyone can read from these repositories –
they really help people get started quickly! You could also use
[*Trusted Builds*](#trusted-builds) if you need to keep
control of who accesses your images, but we will only refer to public
repositories in these examples.

-   Top-level repositories can easily be recognized by **not** having a
    `/` (slash) in their name. These repositories
    can generally be trusted.
-   User repositories always come in the form of
    `<username>/<repo_name>`. This is what your
    published images will look like if you push to the public Central
    Registry.
-   Only the authenticated user can push to their *username* namespace
    on the Central Registry.
-   User images are not checked, it is therefore up to you whether or
    not you trust the creator of this image.

## Find Public Images on the Central Index

You can search the Central Index [online](https://index.docker.io) or
using the command line interface. Searching can find images by name,
user name or description:

    $ sudo docker help search
    Usage: docker search NAME

    Search the docker index for images

      -notrunc=false: Don't truncate output
    $ sudo docker search centos
    Found 25 results matching your query ("centos")
    NAME                             DESCRIPTION
    centos
    slantview/centos-chef-solo       CentOS 6.4 with chef-solo.
    ...

There you can see two example results: `centos` and
`slantview/centos-chef-solo`. The second result
shows that it comes from the public repository of a user,
`slantview/`, while the first result
(`centos`) doesn’t explicitly list a repository so
it comes from the trusted Central Repository. The `/`
character separates a user’s repository and the image name.

Once you have found the image name, you can download it:

    # sudo docker pull <value>
    $ sudo docker pull centos
    Pulling repository centos
    539c0211cd76: Download complete

What can you do with that image? Check out the
[*Examples*](../../examples/#example-list) and, when you’re ready with
your own image, come back here to learn how to share it.

## Contributing to the Central Registry

Anyone can pull public images from the Central Registry, but if you
would like to share one of your own images, then you must register a
unique user name first. You can create your username and login on the
[central Docker Index online](https://index.docker.io/account/signup/),
or by running

    sudo docker login

This will prompt you for a username, which will become a public
namespace for your public repositories.

If your username is available then `docker` will
also prompt you to enter a password and your e-mail address. It will
then automatically log you in. Now you’re ready to commit and push your
own images!

## Committing a Container to a Named Image

When you make changes to an existing image, those changes get saved to a
container’s file system. You can then promote that container to become
an image by making a `commit`. In addition to
converting the container to an image, this is also your opportunity to
name the image, specifically a name that includes your user name from
the Central Docker Index (as you did a `login`
above) and a meaningful name for the image.

    # format is "sudo docker commit <container_id> <username>/<imagename>"
    $ sudo docker commit $CONTAINER_ID myname/kickassapp

## Pushing a repository to its registry

In order to push an repository to its registry you need to have named an
image, or committed your container to a named image (see above)

Now you can push this repository to the registry designated by its name
or tag.

    # format is "docker push <username>/<repo_name>"
    $ sudo docker push myname/kickassapp

## Trusted Builds

Trusted Builds automate the building and updating of images from GitHub,
directly on `docker.io` servers. It works by adding
a commit hook to your selected repository, triggering a build and update
when you push a commit.

### To setup a trusted build

1.  Create a [Docker Index account](https://index.docker.io/) and login.
2.  Link your GitHub account through the `Link Accounts`
 menu.
3.  [Configure a Trusted build](https://index.docker.io/builds/).
4.  Pick a GitHub project that has a `Dockerfile`
    that you want to build.
5.  Pick the branch you want to build (the default is the
    `master` branch).
6.  Give the Trusted Build a name.
7.  Assign an optional Docker tag to the Build.
8.  Specify where the `Dockerfile` is located. The
    default is `/`.

Once the Trusted Build is configured it will automatically trigger a
build, and in a few minutes, if there are no errors, you will see your
new trusted build on the Docker Index. It will will stay in sync with
your GitHub repo until you deactivate the Trusted Build.

If you want to see the status of your Trusted Builds you can go to your
[Trusted Builds page](https://index.docker.io/builds/) on the Docker
index, and it will show you the status of your builds, and the build
history.

Once you’ve created a Trusted Build you can deactivate or delete it. You
cannot however push to a Trusted Build with the `docker push`
command. You can only manage it by committing code to your
GitHub repository.

You can create multiple Trusted Builds per repository and configure them
to point to specific `Dockerfile`‘s or Git branches.

## Private Registry

Private registries and private shared repositories are only possible by
hosting [your own
registry](https://github.com/dotcloud/docker-registry). To push or pull
to a repository on your own registry, you must prefix the tag with the
address of the registry’s host (a `.` or
`:` is used to identify a host), like this:

    # Tag to create a repository with the full registry location.
    # The location (e.g. localhost.localdomain:5000) becomes
    # a permanent part of the repository name
    sudo docker tag 0u812deadbeef localhost.localdomain:5000/repo_name

    # Push the new repository to its home location on localhost
    sudo docker push localhost.localdomain:5000/repo_name

Once a repository has your registry’s host name as part of the tag, you
can push and pull it like any other repository, but it will **not** be
searchable (or indexed at all) in the Central Index, and there will be
no user name checking performed. Your registry will function completely
independently from the Central Index.

<iframe width="640" height="360" src="//www.youtube.com/embed/CAewZCBT4PI?rel=0" frameborder="0" allowfullscreen></iframe>

See also

[Docker Blog: How to use your own
registry](http://blog.docker.io/2013/07/how-to-use-your-own-registry/)

## Authentication File

The authentication is stored in a json file, `.dockercfg`
located in your home directory. It supports multiple registry
urls.

`docker login` will create the
"[https://index.docker.io/v1/](https://index.docker.io/v1/)" key.

`docker login https://my-registry.com` will create
the "[https://my-registry.com](https://my-registry.com)" key.

For example:

    {
         "https://index.docker.io/v1/": {
                 "auth": "xXxXxXxXxXx=",
                 "email": "email@example.com"
         },
         "https://my-registry.com": {
                 "auth": "XxXxXxXxXxX=",
                 "email": "email@my-registry.com"
         }
    }

The `auth` field represents
`base64(<username>:<password>)`