c57c560d90
This one was a massive pain to track down. The original symptom was an error message from rootless Podman trying to make a container in a pod. I unfortunately did not look at the error message closely enough to realize that the namespace in question was the cgroup namespace (the reproducer pod was explicitly set to only share the network namespace), else this would have been quite a bit shorter. I spent considerable effort trying to track down differences between the inspect output of the two containers, and when that failed I was forced to resort to diffing the OCI specs. That finally proved fruitful, and I was able to determine what should have been obvious all along: the container was joining the cgroup namespace of the infra container when it really ought not to have. From there, I discovered a variable collision in pod config. The UsePodCgroup variable means "create a parent cgroup for the pod and join containers in the pod to it". Unfortunately, it is very similar to UsePodUTS, UsePodNet, etc, which mean "the pod shares this namespace", so an accessor was accidentally added for it that indicated the pod shared the cgroup namespace when it really did not. Once I realized that, it was a quick fix - add a bool to the pod's configuration to indicate whether the cgroup ns was shared (distinct from UsePodCgroup) and use that for the accessor. Also included are fixes for `podman inspect` and `podman pod inspect` that fix them to actually display the state of the cgroup namespace (for container inspect) and what namespaces are shared (for pod inspect). Either of those would have made tracking this down considerably quicker. Fixes #6149 Signed-off-by: Matthew Heon <mheon@redhat.com>
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.
- Latest Version: 1.9.1
- Continuous Integration:
- GoDoc:
- Automated continuous release downloads (including remote-client):
Overview and scope
At a high level, the scope of libpod and Podman is the following:
- Support multiple image formats including the OCI and Docker 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.
- Support for a Docker-compatible CLI interface through Podman.
- Support for a REST API providing both a Docker-compatible interface and an improved interface exposing advanced Podman functionality.
- Integration with CRI-O to share containers and backend code.
Podman presently only supports running containers on Linux. However, we are building a remote client which can run on Windows and OS X and manage Podman containers on a Linux system via the REST API using SSH tunneling.
Roadmap
- Complete the Podman REST API and Podman v2, which will be able to connect to remote Podman instances via this API
- Integrate libpod into CRI-O to replace its existing container management backend
- Further work on the podman pod command
- Further improvements on rootless containers
Communications
If you think you've identified a security issue in the project, please DO NOT report the issue publicly via the Github issue tracker, mailing list, or IRC.
Instead, send an email with as many details as possible to security@lists.podman.io. This is a private mailing list for the core maintainers.
For general questions and discussion, please use the
IRC #podman channel on irc.freenode.net.
For discussions around issues/bugs and features, you can use the GitHub issues and PRs tracking system.
There is also a mailing list at lists.podman.io.
You can subscribe by sending a message to podman-join@lists.podman.io with the subject subscribe.
Rootless
Podman can be easily run as a normal user, without requiring a setuid binary.
When run without root, Podman containers use user namespaces to set root in the container to the user running Podman.
Rootless Podman runs locked-down containers with no privileges that the user running the container does not have.
Some of these restrictions can be lifted (via --privileged, for example), but rootless containers will never have more privileges than the user that launched them.
If you run Podman as your user and mount in /etc/passwd from the host, you still won't be able to change it, since your user doesn't have permission to do so.
Almost all normal Podman functionality is available, though there are some shortcomings. Any recent Podman release should be able to run rootless without any additional configuration, though your operating system may require some additional configuration detailed in the install guide.
A little configuration by an administrator is required before rootless Podman can be used, the necessary setup is documented here.
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. If Kubernetes does not fit your requirements, there are other third-party tools that support the docker-compose format such as kompose and podman-compose that might be appropriate for your environment. This situation may change with the addition of the REST API.
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.
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 REST API. Please note that the API is still in its early stages and not yet stable.
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.
Basic Setup and Use of Podman in a Rootless environment A tutorial showing the setup and configuration necessary to run Rootless Podman.
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. For building container images via Dockerfiles, Podman uses Buildah's golang API and can be installed independently from Buildah.
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.
Podman Legacy API (Varlink)
Podman offers a Varlink-based API for remote management of containers. However, this API has been deprecated by the REST API. Varlink support is in maintenance mode, and will be removed in a future release. For more details, you can see this blog.