Buildah

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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.

Configuration

Enable support to build unprivileged containers

This article or section is being considered for removal.

Reason: Duplicates Podman#Set subuid and subgid. (Discuss in Talk:Buildah)

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, follow the steps bellow 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.

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 the user you are using for test — you should log in as such user since su without the --login flag will not set XDG_RUNTIME_DIR and other environmental variables to correct values.

Usage

See the Buildah tutorials.

Troubleshooting

WARN[0000] "/" is not a shared mount, this could cause issues or missing mounts with rootless containers

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

$ findmnt -o PROPAGATION /
PROPAGATION
private

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

# mount --make-shared /

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: 

/etc/fstab
# <device>                                <dir> <type> <options> <dump> <fsck>
UUID=0a3407de-014b-458b-b5c1-848e92a327a3 /     ext4   defaults,shared   0      1

See also