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PODMAN logo

Library and tool for running OCI-based containers in Pods

Libpod provides a library for applications looking to use the Container Pod concept, popularized by Kubernetes. Libpod also contains the Pod Manager tool (Podman). Podman manages pods, containers, container images, and container volumes.

Overview and scope

At a high level, the scope of libpod and podman is the following:

  • Support multiple image formats including the existing Docker/OCI image formats.
  • Support for multiple means to download images including trust & image verification.
  • Container image management (managing image layers, overlay filesystems, etc).
  • Full management of container lifecycle
  • Support for pods to manage groups of containers together
  • Resource isolation of containers and pods.
  • Integration with CRI-O to share containers and backend code.

This project tests all builds against each supported version of Fedora, the latest released version of Red Hat Enterprise Linux, and the latest Ubuntu Long Term Support release. The community has also reported success with other Linux flavors.

Roadmap

  1. Allow the Podman CLI to use a Varlink backend to connect to remote Podman instances
  2. Integrate libpod into CRI-O to replace its existing container management backend
  3. Further work on the podman pod command
  4. Further improvements on rootless containers

Out of scope

  • Specializing in signing and pushing images to various storage backends. See Skopeo for those tasks.
  • Container runtimes daemons for working with the Kubernetes CRI interface. CRI-O specializes in that.
  • Supporting docker-compose. We believe that Kubernetes is the defacto standard for composing Pods and for orchestrating containers, making Kubernetes YAML a defacto standard file format. Hence, Podman allows the creation and execution of Pods from a Kubernetes YAML file (see podman-play-kube). Podman can also generate Kubernetes YAML based on a container or Pod (see podman-generate-kube), which allows for an easy transition from a local development environment to a production Kubernetes cluster.

OCI Projects Plans

The plan is to use OCI projects and best of breed libraries for different aspects:

  • Runtime: runc (or any OCI compliant runtime) and OCI runtime tools to generate the spec
  • Images: Image management using containers/image
  • Storage: Container and image storage is managed by containers/storage
  • Networking: Networking support through use of CNI
  • Builds: Builds are supported via Buildah.
  • Conmon: Conmon is a tool for monitoring OCI runtimes. It is part of the CRI-O package

Podman Information for Developers

For blogs, release announcements and more, please checkout the podman.io website!

Installation notes Information on how to install Podman in your environment.

OCI Hooks Support Information on how Podman configures OCI Hooks to run when launching a container.

Podman API Documentation on the Podman API using Varlink.

Podman Commands A list of the Podman commands with links to their man pages and in many cases videos showing the commands in use.

Podman Troubleshooting Guide A list of common issues and solutions for Podman.

Podman Usage Transfer Useful information for ops and dev transfer as it relates to infrastructure that utilizes Podman. This page includes tables showing Docker commands and their Podman equivalent commands.

Tutorials Tutorials on using Podman.

Remote Client A brief how-to on using the Podman remote-client.

Release Notes Release notes for recent Podman versions

Contributing Information about contributing to this project.

Buildah and Podman relationship

Buildah and Podman are two complementary open-source projects that are available on most Linux platforms and both projects reside at GitHub.com with Buildah here and Podman here. Both, Buildah and Podman are command line tools that work on Open Container Initiative (OCI) images and containers. The two projects differentiate in their specialization.

Buildah specializes in building OCI images. Buildah's commands replicate all of the commands that are found in a Dockerfile. This allows building images with and without Dockerfiles while not requiring any root privileges. Buildah’s ultimate goal is to provide a lower-level coreutils interface to build images. The flexibility of building images without Dockerfiles allows for the integration of other scripting languages into the build process. Buildah follows a simple fork-exec model and does not run as a daemon but it is based on a comprehensive API in golang, which can be vendored into other tools.

Podman specializes in all of the commands and functions that help you to maintain and modify OCI images, such as pulling and tagging. It also allows you to create, run, and maintain those containers created from those images.

A major difference between Podman and Buildah is their concept of a container. Podman allows users to create "traditional containers" where the intent of these containers is to be long lived. While Buildah containers are really just created to allow content to be added back to the container image. An easy way to think of it is the buildah run command emulates the RUN command in a Dockerfile while the podman run command emulates the docker run command in functionality. Because of this and their underlying storage differences, you can not see Podman containers from within Buildah or vice versa.

In short, Buildah is an efficient way to create OCI images while Podman allows you to manage and maintain those images and containers in a production environment using familiar container cli commands. For more details, see the Container Tools Guide.