# ARM images with Packer

Packer builder ARM


Packer came to be a pretty good and flexible tool to build system images. Since it has plenty of support for common things such docker etc, I decided to give it a try and unify image building for my ARM machines.
Almost every hardware platform has it’s unique quirks, so I had to write a plugin that would be extensible enough to support the variety of devices I currently own.

This post is mostly describing the plugin configuration and features, feel free to checkout code on github.com/mkaczanowski/packer-builder-arm for more details

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Packer builder ARM

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This plugin allows you to build or extend ARM system image. It operates in two modes:

  • new - creates empty disk image and populates the rootfs on it
  • reuse - uses already existing image as the base
  • resize - uses already existing image but resize given partition (ie. root)

Plugin mimics standard image creation process, such as:

  • builing base empty image (dd)
  • partitioning (sgdisk / sfdisk)
  • filesystem creation (mkfs.type)
  • partition mapping (losetup)
  • filesystem mount (mount)
  • populate rootfs (tar/unzip/xz etc)
  • setup qemu + chroot
  • customize installation within chroot

The virtualization works via binfmt_misc kernel feature and qemu.

Since the setup varies a lot for different hardware types, the example configuration is available per "board". Currently the following boards are supported (feel free to add more):

  • bananapi-r1 (Archlinux ARM)
  • beaglebone-black (Archlinux ARM, Debian)
  • jetson-nano (Ubuntu)
  • odroid-u3 (Archlinux ARM)
  • odroid-xu4 (Archlinux ARM, Ubuntu)
  • parallella (Ubuntu)
  • raspberry-pi (Archlinux ARM, Raspbian)
  • raspberry-pi-3 (Archlinux ARM (armv8))
  • raspberry-pi-4 (Archlinux ARM (armv7), Ubuntu 20.04 LTS))
  • wandboard (Archlinux ARM)
  • armv7 generic (Alpine, Archlinux ARM)

Quick start

git clone https://github.com/mkaczanowski/packer-builder-arm
cd packer-builder-arm
go mod download
go build

sudo packer build boards/odroid-u3/archlinuxarm.json

Run in Docker

This method is primarily for macOS users where is no native way to use qemu-user-static (or Linux users, who do not want to setup packer and all the tools).

Usage via container from Docker Hub:

docker run --rm --privileged -v /dev:/dev -v ${PWD}:/build mkaczanowski/packer-builder-arm build boards/raspberry-pi/raspbian.json

More system packages (e.g. bmap-tools, zstd) can be added via the parameter -extra-system-packages=...:

docker run --rm --privileged -v /dev:/dev -v ${PWD}:/build mkaczanowski/packer-builder-arm build boards/raspberry-pi/raspbian.json -extra-system-packages=bmap-tools,zstd

Usage via local container build:

Build the container locally:

docker build -t packer-builder-arm -f docker/Dockerfile .

Run packer via the local built container:

docker run --rm --privileged -v /dev:/dev -v ${PWD}:/build packer-builder-arm build boards/raspberry-pi/raspbian.json


  • sfdisk / sgdisk
  • e2fsprogs
  • parted (resize mode)
  • resize2fs (resize mode)
  • qemu-img (resize mode)


Configuration is split into 3 parts:

  • remote file config
  • image config
  • qemu config

Remote file

Describes the remote file that is going to be used as base image or rootfs archive (depending on image_build_method)

"file_urls" : ["http://os.archlinuxarm.org/os/ArchLinuxARM-odroid-xu3-latest.tar.gz"],
"file_checksum_url": "http://hu.mirror.archlinuxarm.org/os/ArchLinuxARM-odroid-xu3-latest.tar.gz.md5",
"file_checksum_type": "md5",
"file_unarchive_cmd": ["bsdtar", "-xpf", "$ARCHIVE_PATH", "-C", "$MOUNTPOINT"],
"file_target_extension": "tar.gz",

The file_unarchive_cmd is optional and should be used if the standard golang archiver can't handle the archive format.

Raw images format (.img or .iso) can be used by defining the file_target_extension appropriately.

Image config

The base image description (size, partitions, mountpoints etc).

"image_build_method": "new",
"image_path": "odroid-xu4.img",
"image_size": "2G",
"image_type": "dos",
"image_partitions": [
        "name": "root",
        "type": "8300",
        "start_sector": "4096",
        "filesystem": "ext4",
        "size": "0",
        "mountpoint": "/"

The plugin doesn't try to detect the image partitions because that varies a lot. Instead it solely depend on image_partitions specification, so you should set that even if you reuse the image (method = reuse).

Qemu config

Anything qemu related:

"qemu_binary_source_path": "/usr/bin/qemu-arm-static",
"qemu_binary_destination_path": "/usr/bin/qemu-arm-static"

Chroot provisioner

To execute command within chroot environment you should use chroot communicator:

"provisioners": [
   "type": "shell",
   "inline": [
     "pacman-key --init",
     "pacman-key --populate archlinuxarm"

This plugin doesn't resize partitions on the base image. However, you can easily expand partition size at the boot time with a systemd service. Here you can find real-life example, where a raspberry pi root-fs partition expands to all available space on sdcard.


To dump image on device you can use custom postprocessor (really wrapper around dd with some sanity checks):

"post-processors": [
     "type": "flasher",
     "device": "/dev/sdX",
     "block_size": "4096",
     "interactive": true


Generating rootfs archive

While image (.img) format is useful for most cases, you might want to use rootfs for other purposes (ex. export to docker). This is how you can generate rootfs archive instead of image:

"image_path": "odroid-xu4.img" # generates image
"image_path": "odroid-xu4.img.tar.gz" # generates rootfs archive

Resizing image

Currently resizing is only limited to expanding single ext{2,3,4} partition with resize2fs. This is often requested feature where already built image is given and we need to expand the main partition to accomodate changes made in provisioner step (ie. installing packages).

To resize a partition you need to select resize mode and set selected partition size to 0, for example:

"image_partitions": [
    "name": "boot",
    "name": "root",
    "size": "0",

Complete example: boards/raspberry-pi/raspbian-resize.json


With artifice plugin you can pass rootfs archive to docker plugins

"post-processors": [
        "type": "artifice",
        "files": ["rootfs.tar.gz"]
        "type": "docker-import",
        "repository": "mkaczanowski/archlinuxarm",
        "tag": "latest"


This is the live example on how to use github actions to push image to docker image registry:

cat .github/workflows/archlinuxarm-armv7-docker.yml

How is this plugin different from solo-io/packer-builder-arm-image



For more examples please see:

tree boards/