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Syslinux Replacement — Mini-Project Notes

Background

Syslinux 6.03 is the last release (2016). The project is dead — no upstream patches, no security fixes, no new hardware support. LibreELEC currently uses syslinux for Generic x86_64 to provide dual-mode boot: BIOS (via gptmbr.bin + mtools install) and UEFI 64-bit (via bootx64.efi / ldlinux.e64). GRUB 2.x is built alongside it to provide bootia32.efi for boards with 32-bit EFI firmware (older Intel Atom).

Discussed in the LE13 planning issue: LibreELEC#8184

Decision: UEFI-only for LE13

The team agreed (CvH, HiassofT, chewitt, heitbaum — Aug/Sep 2024) that UEFI-only is acceptable for LE13:

  • UEFI CSM covers anything less than ~10 years old
  • Users on ancient BIOS-only hardware can install LE12 first; LE13 updates only replace KERNEL and SYSTEM and leave the boot partition untouched, so the existing BIOS boot setup continues to work post-update
  • Going forward without UEFI is not a real option

Candidates Evaluated

Barebox (u-boot fork)

Syslinux UEFI-only

  • The existing syslinux package already ships bootx64.efi / ldlinux.e64
  • Hack-tested UEFI-only mode on BeeLink SER7 — works
  • Avoids replacing the bootloader entirely while dropping dead BIOS code
  • Downside: syslinux is still dead upstream; eventually needs replacing anyway

systemd-boot (sd-boot)

  • Part of systemd; already maintained as part of the systemd project
  • LibreELEC already builds it: commit 3c8c56c8 (2024-08-31) added -Dbootloader=enabled to the systemd meson build for Generic x86_64
  • systemd-boot.efi (installed as bootx64.efi) is built but not yet wired into the image
  • systemd-boot requires a UEFI System Partition and uses Type 1 Boot Loader Specification entries (.conf files in /loader/entries/)
  • The systemd project also has additional UEFI utilities to investigate (e.g. systemd-stub, unified kernel images)
  • Most likely path forward

Current Tree State

What is already in place

File Role
packages/tools/syslinux/package.mk syslinux 6.03 — builds bootx64.efi, ldlinux.e64, gptmbr.bin, syslinux.mtools
packages/tools/grub/package.mk grub 2.14 — builds bootia32.efi only (32-bit EFI for Atom boards)
packages/sysutils/systemd/package.mk:105 -Dbootloader=enabled + pyelftools:host dep for Generic — systemd-boot binary is built
scripts/mkimage Image assembly; see below
projects/Generic/options BOOTLOADER="syslinux"
packages/tools/installer/package.mk Depends on syslinux and grub

scripts/mkimage boot assembly (syslinux path)

Line 84:  dd gptmbr.bin → first 440 bytes of disk (BIOS MBR bootstrap)
Line 140: writes syslinux.cfg to FAT root (BIOS menu)
Line 166: writes grub.cfg to /EFI/BOOT (UEFI menu)
Line 187: syslinux.mtools -i part1.fat (installs BIOS bootloader to FAT)
Line 197: mcopy bootx64.efi  → /EFI/BOOT (syslinux UEFI 64-bit)
Line 198: mcopy ldlinux.e64  → /EFI/BOOT (syslinux UEFI 64-bit loader)
Line 199: mcopy bootia32.efi → /EFI/BOOT (grub UEFI 32-bit for Atom)
Line 200: mcopy grub.cfg     → /EFI/BOOT

Boot menu entries (both syslinux.cfg and grub.cfg): Installer, Live, Run

What is NOT yet done

  • systemd-boot .efi is built but not placed in the image
  • scripts/mkimage has no systemd-boot code path
  • projects/Generic/options still sets BOOTLOADER="syslinux"
  • packages/tools/installer still depends on syslinux/grub
  • No .conf loader entries written by mkimage
  • OVA image creation still patches syslinux.cfg / grub.cfg (lines 301-304)

Work Required to Switch to systemd-boot

  1. scripts/mkimage — add a systemd-boot code path:

    • Skip gptmbr.bin MBR write (UEFI-only; no BIOS bootstrap needed)
    • Skip syslinux.mtools install
    • Copy ${TOOLCHAIN}/usr/lib/systemd/boot/efi/systemd-bootx64.efi → /EFI/BOOT/bootx64.efi
    • Write /loader/loader.conf (timeout, default entry)
    • Write /loader/entries/libreelec-installer.conf, libreelec-live.conf, libreelec-run.conf (each: title, linux /KERNEL, options boot=UUID=… …)
    • Keep bootia32.efi (grub) for 32-bit EFI Atom boards, or drop once confirmed unnecessary

  2. projects/Generic/options — change BOOTLOADER="syslinux" to BOOTLOADER="systemd-boot" (or a new value that mkimage understands)

  3. packages/tools/installer/package.mk — update deps; remove syslinux/grub if no longer needed by the installer runtime

  4. packages/tools/syslinux — evaluate: retire entirely, or keep reduced (UEFI files only for any remaining use in installer flow)

  5. OVA image (lines 298-304 in mkimage) — update to patch loader entry instead of syslinux.cfg

  6. Testing matrix:

    • Fresh USB install → run from disk
    • Live/portable boot
    • Update from LE12 (BIOS boot install) — boot partition left intact, LE13 kernel/system loads
    • UEFI 32-bit Atom board (if keeping bootia32.efi)
    • VM (QEMU/VirtualBox) UEFI boot
    • Secure Boot (future — systemd-boot supports it; syslinux does not)

systemd-boot loader entry format

# /loader/entries/libreelec-run.conf
title   LibreELEC (Run)
linux   /KERNEL
options boot=UUID=<SYSTEM_UUID> disk=UUID=<STORAGE_UUID> quiet
# /loader/loader.conf
timeout 5
default libreelec-installer.conf

Notes

  • systemd-boot requires the EFI System Partition to be mounted at /efi or /boot at runtime for bootctl updates. LibreELEC mounts it at /flash — check if bootctl update flow is needed or if we just install the .efi during image build and never update it from the OS.
  • The grub_live / grub_portable kernel parameters in the current grub.cfg are LibreELEC-specific hooks in the init scripts. With systemd-boot the equivalent parameters need to be in the loader entry options line — confirm init scripts handle both or update them.
  • Secure Boot: systemd-boot can be signed; syslinux cannot. This is a future benefit of switching.