USB
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oliver
Executable
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#!/bin/bash
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set -euo pipefail
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# ---------------------------------------------------------------------------
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# create.sh — Build a bootable Alpine Linux rescue ISO
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#
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# Run inside the Docker build container:
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# docker compose run --rm alpine bash /scripts/create.sh
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#
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# The resulting ISO is a hybrid image: it can be burned to a CD/DVD or
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# written directly to a USB stick with dd.
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# ---------------------------------------------------------------------------
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ALPINE_MIRROR="https://dl-cdn.alpinelinux.org/alpine"
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ALPINE_BRANCH="latest-stable"
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ALPINE_ARCH="x86_64"
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MINIROOTFS_BASE="${ALPINE_MIRROR}/${ALPINE_BRANCH}/releases/${ALPINE_ARCH}"
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ISO="/output/rescue-alpine.iso"
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CHROOT="/mnt/alpine-chroot"
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ISOROOT="/tmp/isoroot"
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mkdir -p /output "$CHROOT" "$ISOROOT"
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# ---------------------------------------------------------------------------
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# 1. Fetch latest Alpine minirootfs
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# ---------------------------------------------------------------------------
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echo "==> Fetching latest Alpine minirootfs index"
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TARBALL=$(curl -fsSL "${MINIROOTFS_BASE}/" \
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| grep -oP 'alpine-minirootfs-[0-9.]+-x86_64\.tar\.gz' \
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| sort -V | tail -1)
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[[ -z "$TARBALL" ]] && { echo "ERROR: could not determine minirootfs tarball" >&2; exit 1; }
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TARBALL_LOCAL="/tmp/${TARBALL}"
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if [[ ! -f "$TARBALL_LOCAL" ]]; then
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echo "==> Downloading ${MINIROOTFS_BASE}/${TARBALL}"
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curl -fsSL -o "$TARBALL_LOCAL" "${MINIROOTFS_BASE}/${TARBALL}"
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else
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echo "==> Using cached ${TARBALL_LOCAL}"
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fi
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# ---------------------------------------------------------------------------
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# 2. Extract minirootfs into chroot
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# ---------------------------------------------------------------------------
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echo "==> Extracting minirootfs into ${CHROOT}"
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tar -xzf "$TARBALL_LOCAL" -C "$CHROOT"
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# ---------------------------------------------------------------------------
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# 3. Copy Nebula binary and config into chroot
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# ---------------------------------------------------------------------------
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echo "==> Installing Nebula binary"
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mkdir -p "${CHROOT}/usr/local/bin"
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cp /nebula/nebula "${CHROOT}/usr/local/bin/nebula"
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chmod +x "${CHROOT}/usr/local/bin/nebula"
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echo "==> Installing Nebula config and certificates"
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mkdir -p "${CHROOT}/etc/nebula"
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cp /nebula/config.yml "${CHROOT}/etc/nebula/config.yml"
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for f in /nebula/*.crt /nebula/*.key; do
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[[ -f "$f" ]] && cp "$f" "${CHROOT}/etc/nebula/"
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done
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# ---------------------------------------------------------------------------
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# 4. Bind-mount virtual filesystems for chroot
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# ---------------------------------------------------------------------------
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echo "==> Bind-mounting virtual filesystems"
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mount --bind /dev "${CHROOT}/dev"
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mount --bind /proc "${CHROOT}/proc"
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mount --bind /sys "${CHROOT}/sys"
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mkdir -p "${CHROOT}/run"
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mount --bind /run "${CHROOT}/run"
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cp /etc/resolv.conf "${CHROOT}/etc/resolv.conf"
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# Make scripts available inside chroot
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mkdir -p "${CHROOT}/scripts"
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mount --bind /scripts "${CHROOT}/scripts"
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# ---------------------------------------------------------------------------
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# 5. Run in-chroot configuration
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# ---------------------------------------------------------------------------
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echo "==> Running chroot-setup.sh inside chroot"
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chroot "$CHROOT" /bin/sh /scripts/chroot-setup.sh
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# ---------------------------------------------------------------------------
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# 6. Unmount virtual filesystems
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# ---------------------------------------------------------------------------
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echo "==> Unmounting virtual filesystems"
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umount "${CHROOT}/scripts" || true
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umount "${CHROOT}/run" || true
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umount "${CHROOT}/sys" || true
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umount "${CHROOT}/proc" || true
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umount "${CHROOT}/dev" || true
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# ---------------------------------------------------------------------------
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# 7. Pack the full system as a squashfs (xz compressed)
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# ---------------------------------------------------------------------------
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echo "==> Creating squashfs from chroot (xz — this may take a while)"
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mksquashfs "$CHROOT" "${ISOROOT}/rootfs.squashfs" \
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-comp xz -Xdict-size 100% -noappend \
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-e boot/initramfs-lts 2>/dev/null || \
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mksquashfs "$CHROOT" "${ISOROOT}/rootfs.squashfs" \
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-comp xz -noappend
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echo " squashfs size: $(du -sh "${ISOROOT}/rootfs.squashfs" | cut -f1)"
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# ---------------------------------------------------------------------------
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# 8. Copy kernel into ISO root
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# ---------------------------------------------------------------------------
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echo "==> Copying kernel"
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cp "${CHROOT}/boot/vmlinuz-lts" "${ISOROOT}/vmlinuz"
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# ---------------------------------------------------------------------------
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# 9. Build tiny initramfs: busybox + init script that mounts the squashfs
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# ---------------------------------------------------------------------------
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echo "==> Building tiny initramfs"
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INITRD="/tmp/initrd"
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rm -rf "$INITRD"
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mkdir -p "${INITRD}"/{bin,dev,proc,sys,mnt/boot,mnt/squash,mnt/upper,mnt/work,mnt/newroot}
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# Static busybox — no external library deps
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BBOX=$(find /bin /usr/bin /usr/sbin -name 'busybox.static' -o -name 'busybox' 2>/dev/null \
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| xargs -r file 2>/dev/null | grep -i 'statically linked' | cut -d: -f1 | head -1)
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[[ -z "$BBOX" ]] && { echo "ERROR: cannot find a statically linked busybox" >&2; exit 1; }
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echo " using static busybox: $BBOX"
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cp "$BBOX" "${INITRD}/bin/busybox"
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chmod +x "${INITRD}/bin/busybox"
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for cmd in sh mount umount mkdir mknod switch_root mdev sleep; do
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ln -sf busybox "${INITRD}/bin/${cmd}"
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done
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cat > "${INITRD}/init" <<'INIT_EOF'
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#!/bin/sh
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mount -t proc none /proc
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mount -t sysfs none /sys
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mount -t devtmpfs none /dev 2>/dev/null || mdev -s
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# Scan block devices for the ISO containing rootfs.squashfs
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found=0
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for try in 1 2 3 4 5; do
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for dev in /dev/sr0 /dev/sda /dev/sda1 /dev/sdb /dev/sdb1 /dev/sdc /dev/sdc1; do
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[ -b "$dev" ] || continue
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mount -t iso9660 -o ro "$dev" /mnt/boot 2>/dev/null || \
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mount -o ro "$dev" /mnt/boot 2>/dev/null || continue
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if [ -f /mnt/boot/rootfs.squashfs ]; then
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found=1
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break 2
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fi
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umount /mnt/boot 2>/dev/null
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done
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sleep 1
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done
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if [ "$found" != "1" ]; then
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echo "ERROR: rootfs.squashfs not found — dropping to shell"
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exec sh
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fi
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mount -t squashfs -o ro /mnt/boot/rootfs.squashfs /mnt/squash
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mount -t tmpfs tmpfs /mnt/upper
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mkdir -p /mnt/upper/rw /mnt/upper/work
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mount -t overlay overlay \
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-o lowerdir=/mnt/squash,upperdir=/mnt/upper/rw,workdir=/mnt/upper/work \
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/mnt/newroot
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exec switch_root /mnt/newroot /sbin/init
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INIT_EOF
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chmod +x "${INITRD}/init"
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( cd "$INITRD" && find . | cpio --quiet -oH newc | gzip -9 ) > "${ISOROOT}/initramfs.gz"
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echo " initramfs size: $(du -sh "${ISOROOT}/initramfs.gz" | cut -f1)"
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echo " initramfs contents:"
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zcat "${ISOROOT}/initramfs.gz" | cpio -t 2>/dev/null
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# ---------------------------------------------------------------------------
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# 10. Build ISO with grub-mkrescue (BIOS + UEFI hybrid)
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# grub-mkrescue uses its own file loader — no BIOS INT 13h size limits.
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# ---------------------------------------------------------------------------
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echo "==> Writing GRUB config"
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mkdir -p "${ISOROOT}/boot/grub"
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cat > "${ISOROOT}/boot/grub/grub.cfg" <<'EOF'
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set timeout=5
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set default=0
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menuentry "Alpine Linux USB Rescue" {
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linux /vmlinuz quiet init=/sbin/init
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initrd /initramfs.gz
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}
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EOF
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echo "==> Building hybrid ISO with grub-mkrescue: ${ISO}"
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grub-mkrescue -o "$ISO" "$ISOROOT" -- -V ALPINE_RESCUE
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# ---------------------------------------------------------------------------
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# Done
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# ---------------------------------------------------------------------------
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ISO_SIZE=$(du -sh "$ISO" | cut -f1)
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echo ""
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echo "================================================================"
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echo " Build complete!"
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echo " ISO : ${ISO} (${ISO_SIZE})"
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echo ""
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echo " Burn to USB:"
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echo " dd if=${ISO} of=/dev/sdX bs=4M status=progress && sync"
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echo ""
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echo " Burn to CD/DVD:"
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echo " cdrecord dev=/dev/sr0 ${ISO}"
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echo ""
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echo " Default login : root / alpine"
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echo " Nebula tunnel : auto-starts on boot (needs certs in nebula/)"
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echo "================================================================"
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