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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 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 – 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 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 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 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, 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 and login.
  2. Link your GitHub account through the Link Accounts menu.
  3. Configure a Trusted build.
  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 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. 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.

See also

Docker Blog: 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/" key.

docker login https://my-registry.com will create the "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>)