Ubuntu Autoinstall ISO and Cloud-Init Seed Floppy Builder

This project simplifies the creation of:

• A custom Ubuntu Autoinstall ISO for fully automated installations
• A VFAT-formatted "cidata" floppy image with cloud-init configuration (NoCloud data source)

All processes are managed through a single Makefile.

Features

• Automatic dependency checks for ISO builds and required-file checks
• Customizable GRUB menu
• Non-interactive scripts: controlled entirely via make
• VFAT floppy image production using a temporary mount point

Typical Use Cases

• Provisioning multiple Ubuntu servers quickly and consistently in a datacenter or virtualized environment
• Automated lab or testbed setup
• Infrastructure as Code (IaC) deployments

Requirements

Ubuntu Host Packages

Install the following packages on your Ubuntu host:

sudo apt install curl p7zip-full xorriso dosfstools

Note: sudo is required for make cidata to create and mount the floppy image as a loop device.

You also need roughly 8 GB free on the build host: about 3 GB for the downloaded ISO, the same again for the extracted tree, and the rebuilt ISO on top.

Preparation

Provide the following files in your project directory:

File	Purpose
meta-data.yml	Cloud-init meta-data file (used by both ISO and
	floppy targets)
user-data.yml	Cloud-init user-data file (used by both ISO and
	floppy targets)
grub-autoinstall.menu	GRUB menu entries for the autoinstall ISO

The repo includes three user-data variants to choose from:

• user-data-bios.yml — BIOS-only installs
• user-data-efi.yml — EFI-only installs
• user-data-bios+efi.yml — dual BIOS/EFI installs

Copy the appropriate one to user-data.yml before building:

cp user-data-bios+efi.yml user-data.yml

The ubuntu user's password is ubuntu. This is deliberately a bootstrap credential: these hosts are handed to configuration management immediately after install, and the first pass rotates it. Treat the window between first boot and that pass as the exposure, and keep provisioning on a trusted segment.

If you are not following that workflow, change the hash in the identity section before deploying — generate a replacement with openssl passwd -6.

Minimum Target Disk Size

The fixed logical volumes total 27 GiB before lvm_part (size: -1) claims anything, so the install disk must be at least 28 GiB — 27 GiB of volumes plus a 1 GiB boot partition and the 1 MiB BIOS grub reserve.

A 20 GB VM disk — a natural default — fails during partitioning. This is separate from the build-host space noted above. Shrink the lvm_partition sizes if you want a smaller target.

Example grub-autoinstall.menu

menuentry "Ubuntu Server Autoinstall" {
    set gfxpayload=keep
    linux /casper/vmlinuz autoinstall ds=nocloud\;s=/cdrom/server/ ---
    initrd /casper/initrd
}

Usage

1. Create the Custom Ubuntu Autoinstall ISO

Run:

make

This command:

• Downloads the Ubuntu server ISO
• Extracts it
• Adds autoinstall files
• Patches GRUB
• Creates ubuntu-26.04-autoinstall.iso by default

You can boot this ISO in a virtual machine or on physical hardware for an unattended installation.

2. Create the Cloud-Init "cidata" VFAT Floppy Image

Run (requires root privileges):

sudo make cidata

Output: cidata.img (1.44MB VFAT-formatted floppy image)

Contents:

• meta-data
• user-data

Use this image as a secondary disk ("cidata") in your hypervisor for NoCloud-based installs. For example:

• Proxmox: Add as a "floppy" to the VM
• QEMU: Use with -drive file=cidata.img,if=floppy,format=raw,readonly=on

3. Clean Up Build Artifacts

Run:

make clean

clean deliberately keeps the downloaded ISO so you do not have to re-fetch several GB. Use make distclean to remove that as well.

4. Extract Kernel/Initrd for Netboot (kernel-extractor.sh)

kernel-extractor.sh mounts an Ubuntu ISO (loopback) and copies out the kernel, initrd, and every root filesystem image — useful for iPXE or other netboot setups where the kernel and initrd are served directly rather than booted from an ISO. This script is standalone and not wired into the Makefile.

It copies all .squashfs images, not just one. Since roughly 23.04 the live-server ISO no longer ships a single filesystem.squashfs; it carries a layered set (ubuntu-server-minimal.squashfs, then ubuntu-server-minimal.ubuntu-server.squashfs, and so on) that is stacked at boot and is useless a layer at a time.

sudo ./kernel-extractor.sh <path-to.iso> <output-dir>

Requires root (or equivalent loopback-mount privileges) to mount the ISO.

Customization

• Ubuntu Release: Edit VERSION in the Makefile to change the Ubuntu release. The current default is 26.04.
• GRUB Menu: Modify grub-autoinstall.menu to add or edit GRUB menu entries, including different kernel arguments for multiple install modes. Rename the entries freely — the patch rule brackets whatever it inserts between UBUNTU-AUTOINSTALL-MENU-BEGIN / -END comment markers and rewrites that block on every build, so menu edits are picked up and the entries never accumulate. Do not hand-edit between those markers; the next build discards it. The patch rule also sets set default="0" so the autoinstall entry is the one that boots unattended.
• Cloud-Init Configuration: Use valid cloud-init syntax in meta-data.yml and user-data.yml.

Example Seed grub-autoinstall.menu

menuentry "Ubuntu Server Autoinstall" {
    set gfxpayload=keep
    linux /casper/vmlinuz autoinstall ds=nocloud ---
    initrd /casper/initrd
}

When the cloud-init files are on a floppy, some documentation recommends setting the nocloud device:

    linux /casper/vmlinuz autoinstall ds=nocloud\;s=/dev/fd0/ ---

Example iPXE Menu Entry

The Ubuntu Autoinstall ISO can be used in a iPXE setup. Use kernel-extractor.sh to pull vmlinuz and initrd out of the ISO built above. The following iPXE menu uses the cloud-init user-data file in the uai directory on an iPXE server:

/tftpboot/uai
├── /tftpboot/uai/initrd
├── /tftpboot/uai/server
│   ├── /tftpboot/uai/server/meta-data
│   └── /tftpboot/uai/server/user-data
├── /tftpboot/uai/uai.iso
└── /tftpboot/uai/vmlinuz

:uai
kernel http://10.0.0.6/uai/vmlinuz
initrd http://10.0.0.6/uai/initrd
imgargs vmlinuz initrd=initrd ip=dhcp \
    url=http://10.0.0.6/uai/uai.iso autoinstall \
    cloud-config-url=http://10.0.0.6/uai/server/user-data ---
boot

Troubleshooting

• Missing Dependencies: The default make target checks for required commands before building the ISO. The cidata target checks its own (mkfs.vfat, fsck.fat, mount, umount, dd).
• Root Privileges: If you see "must be run as root" when building cidata, use sudo make cidata.
• Autoinstall Issues: If the VM does not detect the autoinstall from the ISO, try attaching cidata.img as a floppy or secondary disk.

References

https://en.wikipedia.org/wiki/GUID_Partition_Table#Partition_type_GUIDs

https://askubuntu.com/q/1403546

Author, License, and Disclaimer

• Author: Copyright (c) 2023-2026 Jack Bailey
• License: MIT
• Disclaimer: Use at your own risk!