Make Alpine Linux VM Image

This project provides a script for making customized Alpine Linux disk images for x86_64 and aarch64 ^[1] virtual machines. You can choose between BIOS mode (using Syslinux, only for x86_64) and UEFI mode (using Linux EFI stub). It’s quite simple (400 LoC of shell), fast (~32 seconds on GitHub Actions), requires minimum dependencies (QEMU and filesystem tools).

Tip	Don’t need VM, just wanna chroot into Alpine Linux? Try alpine-chroot-install! Or do you want to create a custom rootfs? Then alpine-make-rootfs is for you!

Requirements

• Linux system with common userland (Busybox or GNU coreutils)

• POSIX-sh compatible shell (e.g. Busybox ash, dash, Bash, ZSH)

• qemu-img and qemu-nbd tools

• rsync (needed only for --fs-skel-dir)

• sfdisk (needed only for --partition, --boot-mode UEFI and non-x86 architectures)

• mdev or udevadm (needed only for --partition, --boot-mode UEFI and non-x86 architectures if device hotplug doesn’t work)

• e2fsprogs (for ext4), btrfs-progs (for Btrfs), or xfsprogs (for XFS)

• dosfstools (needed only for --boot-mode UEFI and non-x86 architectures)

All dependencies except the first two are automatically installed by the script when running on Alpine Linux.

Usage

Read documentation in alpine-make-vm-image. See .github/workflows/ci.yml for GitHub Actions example.

You can copy alpine-make-vm-image into your repository or download it on demand, e.g.:

wget https://raw.githubusercontent.com/alpinelinux/alpine-make-vm-image/v0.13.0/alpine-make-vm-image \
    && echo '0fe2deca927bc91eb8ab32584574eee72a23d033  alpine-make-vm-image' | sha1sum -c \
    || exit 1

Or, if you are on Alpine Linux, you can simply install the alpine-make-vm-image package.

Howtos

Create images for aarch64 on x86_64 host

All you need to do is install the QEMU User space emulator for aarch64 and register it in binfmt_misc as the interpreter for aarch64 binaries.

On Alpine Linux

apk add qemu-aarch64 qemu-openrc
rc-service qemu-binfmt start

On Debian/Ubuntu

apt-get install -y --no-install-recommends binfmt-support qemu-user-static
update-binfmts --enable

On Fedora

dnf install qemu-user-static

On GitHub Actions

- name: Install qemu-aarch64 and register in binfmt
  uses: jirutka/setup-alpine@v1
  with:
    arch: aarch64

See .github/workflows/ci.yml for a complete example.

After that, run alpine-make-vm-image with the option --arch aarch64.

Create aarch64 image with Alpine v3.18 or older

The Linux kernel (linux-virt, linux-lts or linux-edge package) in Alpine v3.18 and earlier doesn’t have EFI_ZBOOT enabled, so EFI stub cannot load a compressed vmlinuz. We backported it to v3.18, but then we had to revert it due to a problem with Grub (see alpine/aports#15263).

If you want to build an image with an older branch of Alpine Linux, you can, but you must install the kernel from the v3.19 branch (or newer). This is relatively safe because the kernel package doesn’t have any dynamic dependencies.

1. Create a repositories file with a pinned main repository from v3.19, e.g.:

   @v319 https://dl-cdn.alpinelinux.org/alpine/v3.19/main
   https://dl-cdn.alpinelinux.org/alpine/v3.18/main
   https://dl-cdn.alpinelinux.org/alpine/v3.18/community

2. Run alpine-make-vm-image with the options --repositories-file ./repositories and --packages linux-virt@v319 (or linux-lts@v319 if you use --kernel-flavor lts).

This will first install linux-virt from v3.18, but in the later step it will reinstall it from the v3.19 branch.

Create image for VMware (ESXi)

VMware and disk images (virtual disks) is one big mess. You can find that VMware uses the VMDK format, but the problem is that this is not a single format. Actually it has many subformats with very different structure and various (in)compatibility with VMware hypervisors.

When I’ve created a disk image using qemu-img create -f vmdk or converted Qcow2 to VMDK using qemu-img convert -O vmdk, vSphere client loaded this image without any problem, but the data was corrupted. Eventually I found in some old documentation that ESXi does not support “sparse” disks…

So after many trials I found out that the least bad and functional solution is to create Qcow2 image and then convert it to VMDK using:

qemu-img convert -f qcow2 -O vmdk -o adapter_type=lsilogic,subformat=monolithicFlat alpine.qcow2 alpine.vmdk

Unfortunately, this creates a “thick” image, i.e. its size equals the “provisioned space”, not actually used space as in Qcow2. However, you can compress it with gzip to avoid transferring multiple gigabytes of zeros over network.

License

This project is licensed under MIT License. For the full text of the license, see the LICENSE file.

---

1. Supported since Alpine Linux v3.19. See Create aarch64 image with Alpine v3.18 or older.