ubbie.sh

#!/bin/sh -ex

## create new sparese image
dd if=/dev/zero of=ubbie-raw.img bs=1 count=0 seek=1G

## partition the disk
parted -s ubbie-raw.img mklabel gpt
parted -s ubbie-raw.img mkpart primary fat32 1MiB 501MiB
parted -s ubbie-raw.img mkpart primary ext4 501MiB 5GiB
parted -s ubbie-raw.img mkpart primary ext4 5GiB 100%
parted -s ubbie-raw.img toggle 1 esp

## make sure it looks right :)
parted -s ubbie-raw.img print

## create loop device - 7 should be free
losetup -P /dev/loop7 ubbie-raw.img

## format partitions
mkfs.fat -F 32 /dev/loop7p1
mkfs.ext4 -F /dev/loop7p2
mkfs.ext4 -F /dev/loop7p3

## create label for cloud image root
e2label /dev/loop7p2 cloudimg-rootfs

## mount the new system
mkdir -p /mnt/newroot
mount -t ext4 /dev/loop7p2 /mnt/newroot

## download and install rootfs
wget -q -O - \
https://cloud-images.ubuntu.com/releases/22.04/release/ubuntu-22.04-server-cloudimg-amd64-root.tar.xz | \
tar -xvJf - -C /mnt/newroot

## prepare and mount efi partition
mkdir -p /mnt/newroot/boot/efi
mount -t fat32 /dev/loop7p1 /mnt/newroot/boot/efi

## prepare chroot
mount -t proc /proc /mnt/newroot/proc
mount -t sysfs /sys /mnt/newroot/sys
mount -o bind /dev /mnt/newroot/dev
mount -o bind /dev/pts /mnt/newroot/dev/pts

## copy resolver settings
mkdir -p /mnt/newroot/run/systemd/resolve
cp -f /etc/resolv.conf /mnt/newroot/run/systemd/resolve/stub-resolv.conf

## chroot and modify new root
chroot /mnt/newroot /bin/bash << "EOT"
## update apt and install kernel
export DEBIAN_FRONTEND=noninteractive
apt-get update
apt-get install -y linux-generic
apt-get clean
apt-get autoclean

## install grub and update grub config
grub-install --target=x86_64-efi /dev/loop7
update-grub

## add a standard user (password is "ubuntu")
useradd -G admin,sudo -m -U -s /bin/bash -p \
'$6$xcvUejcYaF4ppAWH$mc0xGb7YW985N0YUGRwfQ3HbcnQL70hKTOe0obH7zSqZ0dR5cDL7d6gRTYQd8dTNw4qLTQFQn2tuMaLEMn1IN0' \
ubuntu
EOT

## cleanup chroot mounts
umount /mnt/newroot/boot/efi
umount /mnt/newroot/proc
umount /mnt/newroot/sys
umount /mnt/newroot/dev/pts
umount /mnt/newroot/dev

## clean resolver
rm -f /mnt/newroot/run/systemd/resolve/stub-resolv.conf

## create default network config
cat > /mnt/newroot/etc/systemd/network/80-dhcp.network << "EOT"
[Match]
Name=en*

[Network]
DHCP=yes
EOT

## cleanup root mount, eject alpine iso, and reboot
## you may have to manually remove image from virtualbox
umount /mnt/newroot

## cleanup loop device
losetup -d /dev/loop7

## All done! We have a new system in ubbie-raw.img
## that can be written to any medium to boot a live system