nix

#!/usr/bin/env bash
set -euo pipefail

ISO_URL="https://channels.nixos.org/nixos-24.05/latest-nixos-minimal-x86_64-linux.iso"
DISK="/dev/vda"
ISO_PART="/dev/vda1"
MNT="/mnt/nixos-iso"
ISO_PATH="${MNT}/nixos.iso"

echo "[1/7] checks"
id -u | grep -q '^0$' || { echo "run as root (sudo -i)"; exit 1; }

echo "[2/7] mount iso partition"
mkdir -p "$MNT"
mountpoint -q "$MNT" || mount "$ISO_PART" "$MNT"

echo "[3/7] download nixos iso"
if [ ! -f "$ISO_PATH" ]; then
  wget -O "$ISO_PATH" "$ISO_URL"
fi

echo "[4/7] verify iso"
mkdir -p /tmp/nixos-check
mount -o loop "$ISO_PATH" /tmp/nixos-check
ls /tmp/nixos-check/boot/bzImage >/dev/null
ls /tmp/nixos-check/boot/initrd >/dev/null
umount /tmp/nixos-check

echo "[5/7] write grub.cfg"
mkdir -p "$MNT/boot/grub"
cat > "$MNT/boot/grub/grub.cfg" <<'EOF'
set default=0
set timeout=5

menuentry "Install NixOS from ISO" {
  set root=(hd0,1)
  set isofile=/nixos.iso

  loopback loop (hd0,1)$isofile
  linux (loop)/boot/bzImage iso-scan/filename=$isofile
  initrd (loop)/boot/initrd
}
EOF

echo "[6/7] install grub"
grub-install --root-directory="$MNT" "$DISK"
sync

echo "[7/7] done"
echo "Run: umount $MNT && reboot"