# Buildah

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- Cgroups
- Docker
- Linux Containers

Buildah is a tool that facilitates building Open Container Initiative (OCI) container images. The Buildah package provides a command line tool that can be used to:

- create a working container, either from scratch or using an image as a starting point
- create an image, either from a working container or via the instructions in a Dockerfile
- images can be built in either the OCI image format or the traditional upstream docker image format
- mount a working container's root filesystem for manipulation
- unmount a working container's root filesystem
- use the updated contents of a container's root filesystem as a filesystem layer to create a new image
- delete a working container or an image
- rename a local container

The most widely known alternative for building containers is docker. Do note that Buildah does not run containers, for that you may want to consider podman.

## Installation

Install the buildah and podman packages or, for the development version, the buildah-gitAUR package.

If you want to run as non-root user, also install fuse-overlayfs for better performance and storage space efficiency.

Note: official buildah installation guide points at podman section where advise is given to install fuse-overlayfs before installing podman

## Configuration

### Enable support to build unprivileged containers

Users wishing to use Buildah to build unprivileged containers need to complete additional setup steps before running podman for the first time.

Note: If you are building system dedicated for running unprivileged containers then follow below steps before adding any user - this way you will not have to edit /etc/subuid and /etc/subgid - useradd will do that for you, you only need to run touch /etc/subgid and touch /etc/subuid as root

Firstly, a kernel is required that has support for User Namespaces (a kernel with `CONFIG_USER_NS`). All Arch Linux kernels have support for `CONFIG_USER_NS`.

Finally, create both `/etc/subuid` and `/etc/subgid` to contain the mapping to the containerized uid/gid pairs for each user who shall be able to run the containers.[1] The example below is for the root user (and systemd system unit) and an example user `buildah`:

    /etc/subuid

    buildah:100000:65536

    /etc/subgid

    buildah:100000:65536

If you did run podman before applying the changes above, you will get errors when trying to pull images as an unprivileged user. Run `podman system migrate` to fix it.

If everything went well then after logging out and logging back in `buildah images` should not result in error

Note: If you see errors accessing /run/user/0 then you have probably used su to become user you are using for test - you should log in as such user since su will not set XDG_RUNTIME_DIR and other environmental variables to correct values

## See also

- Buildah Blog Post Series
- Containers Organization GitHub projects
- Podman daemonless container engine

Categories:

- Virtualization
- Sandboxing