Podman

By default, only root is allowed to run containers (or namespaces in kernelspeak). Running rootless Podman improves security as an attacker will not have root privileges over your system, and also allows multiple unprivileged users to run containers on the same machine. See also podman(1) § Rootless mode.

The following packages are required to run Podman in a rootless environment:

First, check the value of by running:

$ sysctl kernel.unprivileged_userns_clone

If it is currently set to , enable it by setting via sysctl or kernel parameter.

In order for users to run rootless Podman, a and configuration entry must exist for each user that wants to use it. New users created using useradd(8) have these entries by default.

# usermod --add-subuids 100000-165535 --add-subgids 100000-165535 username

Rootless Podman uses a pause process to keep the unprivileged namespaces alive. This prevents any change to the and files from being propagated to the rootless containers while the pause process is running. For these changes to be propagated it is necessary to run:

$ podman system migrate

After this, the user/group specified in the above files is able to start and run Podman containers.

The configuration for how and where container images and instances are stored takes place in .

Set the according to the filesystem in use for the storage location (see ).

Podman is able to run images built for different CPU architecture than host using Wikipedia:binfmt_misc system.

To enable it, install and .

systemd comes with systemd-binfmt.service service which should enable new rules.

Verify that binfmt rules have been added:

Podman should now be able to run foreign architecture images. Most commands use the foreign architecture when option is passed.

Example:

Podman 3.0.0 introduces docker-compose support. This requires enabling a Podman socket which pretends to be docker; start the unit. For rootless containers, this requires you to start the user unit instead and set the variable:

$ export DOCKER_HOST="unix://$XDG_RUNTIME_DIR/podman/podman.sock"

To get hostname resolution between containers running install .

$ export DOCKER_BUILDKIT=0

The following command pulls the Arch Linux x86_64 image from Docker Hub.

# podman pull docker.io/archlinux

See the Docker Hub page for a full list of available tags, including versions with and without build tools.

See also README.md.

Alpine Linux is a popular choice for small container images, especially for software compiled as static binaries. The following command pulls the latest Alpine Linux image from Docker Hub:

# podman pull docker.io/alpine

Alpine Linux uses the musl libc implementation instead of the glibc libc implementation used by most Linux distributions. Because Arch Linux uses glibc, there are a number of functional differences between an Arch Linux host and an Alpine Linux container that can impact the performance and correctness of software. A list of these differences is documented in https://wiki.musl-libc.org/functional-differences-from-glibc.html.

Note that dynamically linked software built on Arch Linux (or any other system using glibc) may have bugs and performance problems when run on Alpine Linux (or any other system using a different libc). See , and for examples.

The following command pulls the latest CentOS image from Docker Hub:

# podman pull docker.io/centos

See the Docker Hub page for a full list of available tags for each CentOS release.

The following command pulls the latest Debian image from Docker Hub:

# podman pull docker.io/debian

See the Docker Hub page for a full list of available tags, including both standard and slim versions for each Debian release.

WARN[0000] Failed to add pause process to systemd sandbox cgroup: Process org.freedesktop.systemd1 exited with status 1 

Can be solved using: https://github.com/containers/crun/issues/704

# echo +cpu +cpuset +io +memory +pids > /sys/fs/cgroup/cgroup.subtree_control

WARN[0000]  binary not found, container dns will not be enabled

If you installed netavark as podman network backend you need to install

It may happen that after logging out from machine, Podman containers are stopped. To prevent that, user lingering should be enabled for user running containers:

$ loginctl enable-linger

You can also create user systemd unit as described: https://docs.podman.io/en/latest/markdown/podman-auto-update.1.html#examples

$ docker-compose up

ERRO[0000] failed to move the rootless netns slirp4netns process to the systemd user.slice: Process org.freedesktop.systemd1 exited with status 1

Can be solved by starting/enabling .

Error: building local pause image: finding pause binary: exec: "catatonit": executable file not found in $PATH

Install the package to fix the error.

For details on upgrading from 3.x to 4.0, see the official blog article

Error committing the finished image: error adding layer with blob "sha256:02823fca9b5444c196f1f406aa235213254af9909fca270f462e32793e2260d8": Error processing tar file(exit status 1) permitted operation

Check that the storage driver is overlay in the #Storage configuration.

If you are using AppArmor you might end up with problems when creating container using a bridge network with the plugin enabled:

$ podman network create foo

/home/''user''/.config/cni/net.d/foo.conflist

This can be solved by adding the following lines to :

owner /run/user/[0-9]*/containers/cni/dnsname/*/dnsmasq.conf r,
owner /run/user/[0-9]*/containers/cni/dnsname/*/addnhosts r,
owner /run/user/[0-9]*/containers/cni/dnsname/*/pidfile rw,

And then reloading the AppArmor profile:

# apparmor_parser -R /etc/apparmor.d/usr.sbin.dnsmasq
# apparmor_parser /etc/apparmor.d/usr.sbin.dnsmasq

By default, the registry list is not populated as the files in the package come from upstream. This means that by default, trying to pull any image without specifying the registry will result in an error similar to the following:

Error: short-name "archlinux" did not resolve to an alias and no unqualified-search registries are defined in "/etc/containers/registries.conf"

A starting configuration could be the following:

This is equivalent to the default docker configuration.

A less convenient alternative, but having a higher compatibility with systems without configured shortnames, use the full registry path in the or .

Containerfile

FROM docker.io/archlinux/archlinux

Can be solved: https://bbs.archlinux.org/viewtopic.php?id=253966

$ env DBUS_SESSION_BUS_ADDRESS= podman ...
$ env DBUS_SESSION_BUS_ADDRESS= podman-compose ...

When using to push container images to Docker Hub, the following errors could occur: or . The following hints can help to fix potential issues

• Tag the local image, e.g.,

# podman tag <localImage> docker.io/<dockerHubUsername>/<dockerHubRepository>:<Tag>

• Push the tagged image, e.g.,

# podman push docker.io/<dockerHubUsername>/<dockerHubRepository>:<Tag> docker://docker.io/<dockerHubUsername>/<dockerHubRepository>:<Tag>

• Login to docker.io, the Docker Hub repository and Docker Hub Registry server, e.g.,

# podman login -u <DockerHubUsername> -p <DockerHubPassword> registry-1.docker.io
# podman login -u <DockerHubUsername> -p <DockerHubPassword> docker.io/<dockerHubUsername>/<dockerHubRepository>
# podman login -u <DockerHubUsername> -p <DockerHubPassword> docker.io

• Logout from all registries before the login, e.g.,

# podman logout --all

• Add <dockerHubUsername> as collaborator in the Docker Hub Collaborators tab of the reporsitory

Buildah/Podman running as rootless expects the bind mount to be shared, check if it is set to private:

In this case see mount(8) § Shared_subtree_operations and set temporarily the mount as shared with:

To set it permanently edit /etc/fstab and add the shared option to the desired mount and reboot. It will result in a entry like: