fix(archiso): document/automate block-level USB write to fix ldlinux.c32 error
"failed to load ldlinux.c32" when booting from USB is caused by writing the isohybrid ISO at file level (drag-and-drop, Rufus "ISO" mode, UNetbootin), which destroys the MBR/isolinux layout. The ISO build itself is correct — archiso's bios.syslinux mode installs isolinux.bin + isohdpfx.bin + the c32 modules and applies the isohybrid MBR, and the profile's bootmodes match upstream releng. Add archiso/write-usb.sh: a safe block-level (dd) writer that lists removable disks, refuses partitions and the system/root disk, requires an all-caps YES, unmounts the target, then writes with conv=fsync. build.sh's completion output now points at it and warns that file-level copies cause exactly this error. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>main
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@ -228,6 +228,23 @@ else
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echo "No answerfile — guided (manual) installer will start automatically on boot."
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echo "No answerfile — guided (manual) installer will start automatically on boot."
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fi
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fi
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# ── How to write the ISO to USB ────────────────────────────────────────────────
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# This is an isohybrid image: it MUST be written block-for-block. Copying the
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# file onto a mounted USB, or using Rufus "ISO" mode / UNetbootin, rewrites the
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# layout and the BIOS bootloader then fails with "failed to load ldlinux.c32".
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# Glob (not ls) so filenames are handled safely; date-named ISOs sort ascending,
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# so the last match is the newest build.
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_isos=("$OUT_DIR"/*.iso)
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_built_iso="${_isos[-1]}"
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if [[ -e "$_built_iso" ]]; then
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echo
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echo "To write it to a USB stick (block-level — required for BIOS boot):"
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echo " bash $SCRIPT_DIR/write-usb.sh \"$_built_iso\" /dev/sdX"
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echo " or directly: sudo dd if=\"$_built_iso\" of=/dev/sdX bs=4M conv=fsync status=progress"
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echo " Do NOT drag-and-drop the .iso onto the USB, and avoid Rufus 'ISO' mode"
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echo " (use 'DD' mode) — those cause 'failed to load ldlinux.c32' at boot."
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fi
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# ── Netboot artifacts ──────────────────────────────────────────────────────────
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# ── Netboot artifacts ──────────────────────────────────────────────────────────
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# mkarchiso's 'netboot' build mode (set in profiledef.sh) produces a tarball
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# mkarchiso's 'netboot' build mode (set in profiledef.sh) produces a tarball
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# containing the kernel, initramfs, and airootfs.sfs ready for HTTP-based PXE
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# containing the kernel, initramfs, and airootfs.sfs ready for HTTP-based PXE
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@ -0,0 +1,85 @@
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#!/usr/bin/env bash
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# write-usb.sh — write the M-Archy ISO to a USB stick with a raw, block-level copy.
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#
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# WHY THIS EXISTS:
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# The ISO produced by build.sh is an *isohybrid* image: the BIOS bootloader
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# (isolinux) and its .c32 modules live at fixed offsets referenced by an MBR
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# embedded in the first sectors. A block-level write (dd) reproduces those
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# sectors exactly. Copying the .iso file onto a mounted USB, or using Rufus
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# "ISO" mode / UNetbootin / similar "ISO-to-USB" tools, rewrites the layout and
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# the firmware then fails at boot with: "failed to load ldlinux.c32".
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# Writing the whole device verbatim is the only reliable method, and it boots
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# on both BIOS (isolinux) and UEFI (systemd-boot) machines.
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#
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# USAGE:
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# bash write-usb.sh <iso> <device>
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# e.g. bash write-usb.sh ~/m-archy-out/m-archy-2026.06.26-x86_64.iso /dev/sdb
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# Run with the ISO but no device to list candidate removable disks.
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# -e: abort on error; -u: error on unset vars; -o pipefail: catch pipe failures.
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set -euo pipefail
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ISO="${1:-}"
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DEV="${2:-}"
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die() { printf '\n Error: %s\n\n' "$1" >&2; exit 1; }
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# List whole disks so the operator can identify the USB stick. RM=1 marks a
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# removable device, which is almost always the stick (and never the system disk).
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list_disks() {
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echo "Block devices on this machine (RM=1 means removable — usually your USB):"
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lsblk -dn -o NAME,SIZE,TYPE,RM,MODEL \
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| awk '$3=="disk" {model=""; for(i=5;i<=NF;i++) model=model (i>5?" ":"") $i;
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printf " /dev/%-8s %7s RM=%s %s\n", $1, $2, $4, model}'
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}
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[[ -n "$ISO" ]] || { echo "Usage: bash write-usb.sh <iso> <device>"; echo; list_disks; exit 1; }
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[[ -f "$ISO" ]] || die "ISO not found: $ISO"
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if [[ -z "$DEV" ]]; then
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echo "No target device given for ISO: $ISO"; echo; list_disks
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echo; echo "Re-run as: bash write-usb.sh \"$ISO\" /dev/sdX"; exit 1
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fi
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# ── Safety checks (this operation is destructive) ─────────────────────────────
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[[ -b "$DEV" ]] || die "$DEV is not a block device."
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# Must be a whole disk, not a partition like /dev/sdb1 — dd to a partition would
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# not produce a bootable stick and could corrupt an existing filesystem.
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[[ "$(lsblk -dn -o TYPE "$DEV" 2>/dev/null)" == "disk" ]] \
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|| die "$DEV is not a whole disk. Pass the disk (e.g. /dev/sdb), not a partition."
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# Refuse the disk that currently backs the root filesystem — never overwrite the
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# running system. PKNAME of the root source resolves the parent disk name.
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_root_src=$(findmnt -no SOURCE / 2>/dev/null || true)
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_root_disk=$(lsblk -no PKNAME "$_root_src" 2>/dev/null | head -n1 || true)
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[[ -n "$_root_disk" && "/dev/$_root_disk" == "$DEV" ]] \
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&& die "$DEV holds your root filesystem — refusing to overwrite the running system."
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# A non-removable target is suspicious; warn but allow (some USB enclosures
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# report RM=0). The explicit YES prompt below is the real safeguard.
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[[ "$(lsblk -dn -o RM "$DEV" 2>/dev/null)" == "1" ]] \
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|| echo "WARNING: $DEV is NOT flagged removable — make absolutely sure it is your USB stick."
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echo
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lsblk "$DEV"
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echo
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_size=$(lsblk -dn -o SIZE "$DEV")
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_model=$(lsblk -dn -o MODEL "$DEV" | xargs)
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echo "About to ERASE $DEV (${_size}${_model:+, $_model}) and write:"
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echo " $ISO"
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echo
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read -rp "Type YES (all caps) to proceed: " _ans
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[[ "$_ans" == "YES" ]] || { echo "Aborted."; exit 1; }
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# Unmount any mounted partitions of the target so dd has exclusive access.
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while read -r _part; do
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sudo umount "/dev/$_part" 2>/dev/null || true
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done < <(lsblk -ln -o NAME,TYPE "$DEV" | awk '$2=="part"{print $1}')
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echo "Writing (block-level)…"
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# bs=4M: large blocks for throughput; conv=fsync: flush to the device before dd
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# exits so "Done" really means written; status=progress: live byte counter.
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sudo dd if="$ISO" of="$DEV" bs=4M conv=fsync status=progress
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# Final flush of any remaining kernel buffers for the device.
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sync
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echo
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echo "Done — $DEV is now bootable (BIOS + UEFI)."
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echo "Eject it safely (e.g. 'udisksctl power-off -b $DEV') before unplugging."
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