23-04-2021

Docker Image Download Offline



Estimated reading time: 5 minutes

This document describes basic use of the Notary CLI as a tool supporting DockerContent Trust. For more advanced use cases, you mustrun your own Notary service. Read theuse the Notary client for advanced users documentation.

  • Docker is a set of platform as a service (PaaS) products that use OS-level virtualization to deliver software in packages called containers. Containers are isolated from one another and bundle their own software, libraries and configuration files; they can communicate with each other through well-defined channels.
  • Chocolatey is software management automation for Windows that wraps installers, executables, zips, and scripts into compiled packages. Chocolatey integrates w/SCCM, Puppet, Chef, etc. Chocolatey is trusted by businesses to manage software deployments.

What is Notary

Notary is a tool for publishing and managing trusted collections of content.Publishers can digitally sign collections and consumers can verify integrityand origin of content. This ability is built on a straightforward key managementand signing interface to create signed collections and configure trusted publishers.

With Notary anyone can provide trust over arbitrary collections of data. UsingThe Update Framework (TUF)as the underlying security framework, Notary takes care of the operations necessaryto create, manage, and distribute the metadata necessary to ensure the integrity andfreshness of your content.

Then you can save this image to a file. Sudo docker save -o ubuntuimage.docker ubuntu Transfer the file on the offline computer (USB/CD/whatever) and load the image from the file: sudo docker load -i ubuntuimage.docker (On older versions this was just docker load image.docker, see comments for more info.). Docker image that provides a Minecraft Server that will automatically download selected version at startup - itzg/docker-minecraft-server.

Install Notary

You can download precompiled notary binary for 64 bit Linux or macOS from theNotary repository’sReleases page on Github.

Understand Notary naming

Notary uses Globally Unique Names (GUNs) to identify trust collections. Toenable Notary to run in a multi-tenant fashion, you must use this formatwhen interacting with Docker Hub through the Notary client. When specifyingDocker image names for the Notary client, the GUN format is:

  • For official images (identifiable by the “Official Image” moniker), theimage name as displayed on Docker Hub, prefixed with docker.io/library/. Forexample, if you would normally type docker pull ubuntu you must enter notary{cmd} docker.io/library/ubuntu.
  • For all other images, the image name as displayed on Docker Hub, prefixed by docker.io.

The Docker Engine client takes care of these name expansions for you so do notchange the names you use with the Engine client or API. This is a requirementonly when interacting with the same Docker Hub repositories through the Notaryclient.

Inspect a Docker Hub repository

The most basic operation is listing the available signed tags in a repository.The Notary client used in isolation does not know where the trust repositoriesare located. So, you must provide the -s (or long form --server) flag totell the client which repository server it should communicate with.

The official Docker Hub Notary servers are located athttps://notary.docker.io. If you would like to use your own Notary server,it is important to use the same or a newerNotary version,as the client for feature compatibility (ex: client version 0.2, server/signer version >= 0.2).Additionally, Notary stores your own signing keys,and a cache of previously downloaded trust metadata in a directory, providedwith the -d flag. When interacting with Docker Hub repositories, you mustinstruct the client to use the associated trust directory, which by default isfound at .docker/trust within the calling user’s home directory (failing touse this directory may result in errors when publishing updates to your trustdata):

The output shows us the names of the tags available, the hex encoded sha256digest of the image manifest associated with that tag, the size of the manifest,and the Notary role that signed this tag into the repository. The “targets” roleis the most common role in a simple repository. When a repository has (orexpects) to have collaborators, you may see other “delegated” roles listed assigners, based on the choice of the administrator as to how they organize theircollaborators.

When you run a docker pull command, Docker Engine is using an integratedNotary library (the same one as Notary CLI) to request the mapping of tagto sha256 digest for the one tag you are interested in (or if you passed the--all flag, the client uses the list operation to efficiently retrieve allthe mappings). Having validated the signatures on the trust data, the clientinstructs the Engine to do a “pull by digest”. During this pull, theEngine uses the sha256 checksum as a content address to request and validate theimage manifest from the Docker registry.

Delete a tag

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Notary generates and stores signing keys on the host it’s running on. This meansthat the Docker Hub cannot delete tags from the trust data, they must be deletedusing the Notary client. You can do this with the notary remove command.Again, you must direct it to speak to the correct Notary server. Neitheryou nor the author has permissions to delete tags from the official alpinerepository, so the output below is for demonstration only:

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In the preceding example, the output message indicates that only the removal wasstaged. When performing any write operations they are staged into a change list.This list is applied to the latest version of the trust repository the next timea notary publish is run for that repository.

You can see a pending change by running notary status for the modifiedrepository. The status subcommand is an offline operation and as such, doesnot require the -s flag, however it silently ignores the flag if provided.Failing to provide the correct value for the -d flag may show the wrong(probably empty) change list:

Configure the client

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It is verbose and tedious to always provide the -s and -d flagsmanually to most commands. A simple way to create preconfigured versions of theNotary command is via aliases. Add the following to your .bashrc orequivalent:

More advanced methods of configuration, and additional options, can be found inthe configuration doc and by running notary --help.

docker, Notary, notary-client, docker content trust, content trust

Estimated reading time: 5 minutes

Note: You may have been redirected to this page because there is no longera dynamically-linked Docker package for your Linux distribution.

If you want to try Docker or use it in a testing environment, but you’re not ona supported platform, you can try installing from static binaries. If possible,you should use packages built for your operating system, and use your operatingsystem’s package management system to manage Docker installation and upgrades.Be aware that 32-bit static binary archives do not include the Docker daemon.

Static binaries for the Docker daemon binary are only available for Linux (asdockerd). Static binaries for the Docker client are available for Linux and macOS (as docker).

This topic discusses binary installation for both Linux and macOS:

Install daemon and client binaries on Linux

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Prerequisites

Before attempting to install Docker from binaries, be sure your host machinemeets the prerequisites:

  • A 64-bit installation
  • Version 3.10 or higher of the Linux kernel. The latest version of the kernelavailable for your platform is recommended.
  • iptables version 1.4 or higher
  • git version 1.7 or higher
  • A ps executable, usually provided by procps or a similar package.
  • XZ Utils 4.9 or higher
  • A properly mountedcgroupfs hierarchy; a single, all-encompassing cgroup mountpoint is not sufficient. See Github issues#2683,#3485,#4568).

Secure your environment as much as possible

OS considerations

Enable SELinux or AppArmor if possible.

It is recommended to use AppArmor or SELinux if your Linux distribution supportseither of the two. This helps improve security and blocks certaintypes of exploits. Review the documentation for your Linux distribution forinstructions for enabling and configuring AppArmor or SELinux.

Security Warning

If either of the security mechanisms is enabled, do not disable it as awork-around to make Docker or its containers run. Instead, configure itcorrectly to fix any problems.

Docker daemon considerations

  • Enable seccomp security profiles if possible. SeeEnabling seccomp for Docker.

  • Enable user namespaces if possible. See theDaemon user namespace options.

Install static binaries

Docker

  1. Download the static binary archive. Go tohttps://download.docker.com/linux/static/stable/(or change stable to nightly or test),choose your hardware platform, and download the .tgz file relating to theversion of Docker Engine you want to install.

  2. Extract the archive using the tar utility. The dockerd and dockerbinaries are extracted.

  3. Optional: Move the binaries to a directory on your executable path, suchas /usr/bin/. If you skip this step, you must provide the path to theexecutable when you invoke docker or dockerd commands.

  4. Start the Docker daemon:

    If you need to start the daemon with additional options, modify the abovecommand accordingly or create and edit the file /etc/docker/daemon.jsonto add the custom configuration options.

  5. Verify that Docker is installed correctly by running the hello-worldimage.

    This command downloads a test image and runs it in a container. When thecontainer runs, it prints an informational message and exits.

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Install client binaries on macOS

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The macOS binary includes the Docker client only. It does not include thedockerd daemon.

  1. Download the static binary archive. Go tohttps://download.docker.com/mac/static/stable/x86_64/,(or change stable to nightly or test),and download the .tgz file relating to the version of Docker Engine you wantto install.

  2. Extract the archive using the tar utility. The docker binary isextracted.

  3. Optional: Move the binary to a directory on your executable path, suchas /usr/local/bin/. If you skip this step, you must provide the path to theexecutable when you invoke docker or dockerd commands.

  4. Verify that Docker is installed correctly by running the hello-worldimage. The value of <hostname> is a hostname or IP address running theDocker daemon and accessible to the client.

    This command downloads a test image and runs it in a container. When thecontainer runs, it prints an informational message and exits.

Upgrade static binaries

To upgrade your manual installation of Docker Engine, first stop anydockerd or dockerd.exe processes running locally, then follow theregular installation steps to install the new version on top of the existingversion.

Next steps

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  • Continue to Post-installation steps for Linux.
  • Take a look at the Get started training modules to learn how to build an image and run it as a containerized application.
  • Review the topics in Develop with Docker to learn how to build new applications using Docker.

Docker Image Download Offline

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