Support GRUB 2 BIOS by mika · Pull Request #98 · grml/grml2usb

mika · 2026-03-10T16:31:33Z

grml2usb: use GRUB for BIOS boot, support ISOs without syslinux
grml2iso: use GRUB for BIOS boot, support ISOs without syslinux
grml2iso: drop mkisofs/genisoimage support, require xorriso
grml2iso: drop xorriso version check
grml2iso: various cleanups

(Was sitting on this way to long already and I finally need to stop further optimizing/reworking this 8-) Hope I got things right, or at least we're moving into the right direction! :))

Note: note sure how we want to handle the warnings in grml2iso and whether to exit early or warn about those.

github-actions · 2026-03-10T16:32:11Z

📦 Built packages are ready! Download here.

grml2usb

zeha · 2026-03-10T16:36:56Z

grml2usb


+    # Detect arm64 ISOs and switch to EFI-only mode
+    if grml_flavour.endswith("-arm64") or "-arm64-" in grml_flavour:
+        if options.bootloader in ("syslinux", "grub"):


please merge the two if lines

can we make this conditional on the files present in the iso instead of matching on the name?

done

good idea, hmmm

ok, first one broke ruff :p

tried something(tm) to address 2), while at it

grml2iso

zeha · 2026-03-10T16:40:43Z

grml2iso

+      cp boot/grub/i386-pc/cdboot.img boot/grub/i386-pc/eltorito.img
+      GRUB_BIOS_AVAILABLE=true
+    elif [ -d "/usr/lib/grub/i386-pc" ] ; then
+      # Try to generate GRUB BIOS boot image (requires i386-pc modules)


could investigate dropping this fallback

yeah, not sure about this yet, happy to take any recommendations how to handle/proceed! :)

i wonder what the code block here tries to do. on the 2025.12 PC ISO, we don't have any /boot/grub/i386-pc/*img.
Maybe we should have? is this something to fix in grml-live?

But on our current daily ISOs with GRUB-only we have (example from grml-small-daily20260310build642testing-amd64.iso):

/boot/grub/i386-pc/cdboot.img

/boot/grub/i386-pc/core.img

/boot/grub/i386-pc/eltorito.img

FTR, 2025.12 wasn't GRUB-only yet (as in: we didn't use GRUB for BIOS boot)

github-actions · 2026-03-10T16:57:57Z

📦 Built packages are ready! Download here.

github-actions · 2026-03-10T17:11:21Z

📦 Built packages are ready! Download here.

mika · 2026-03-10T17:13:53Z

Not sure what to do about the DOS/MBR boot sector; partition 1 issue or whether it's really blockdev --rereadpt /dev/loop0 that's failing GitHub actions :-/

zeha · 2026-03-10T17:14:49Z

Not sure what to do about the DOS/MBR boot sector; partition 1 issue or whether it's really blockdev --rereadpt /dev/loop0 that's failing GitHub actions :-/

yeah I was wondering if that is a real or an unrelated failure. It might mean the partition 1 is not marked correctly in the partition table, or something else goes wrong.

Modern Grml ISOs no longer ship isolinux/syslinux files and use GRUB for both BIOS and EFI boot. Update grml2usb to handle this: - Auto-detection now prefers GRUB over syslinux (if grub-install is available) - GRUB installs directly to MBR for simpler + more reliable BIOS boot - Skip legacy mbrldr chainloader when using GRUB - Detect arm64 ISOs by flavour name and auto-switch to EFI-only mode - Gracefully fall back when syslinux files (logo.16) are missing: - To GRUB if grub-install is available - To EFI-only mode otherwise - Deprecate --grub-mbr option (GRUB now always uses MBR) Backwards compatibility: - ISOs with syslinux files still work (--bootloader=syslinux) - Explicit --bootloader= options are honored - All existing command-line options remain functional Support matrix: Host | ISO | ISO has syslinux | Result --------|-------|------------------|--------------------------- amd64 | amd64 | yes | GRUB BIOS+EFI (or syslinux if requested) amd64 | amd64 | no | GRUB BIOS+EFI amd64 | arm64 | no | EFI-only (auto-detected) arm64 | amd64 | yes/no | EFI-only (BIOS N/A on arm64 host) arm64 | arm64 | no | EFI-only See grml/grml-live#483

Recent Grml ISOs no longer ship isolinux/syslinux, as we switched to GRUB also for BIOS boot. Update grml2iso to create hybrid-bootable ISOs using GRUB for BIOS boot when isolinux is unavailable: - Detect available boot method after grml2usb populates the work directory - On arm64 hosts: prefer GRUB over isolinux (isohybrid unavailable) - Fall back to EFI-only boot with helpful warning if BIOS boot impossible - Check source ISO for GRUB boot images before attempting generation - Look for boot.img in ISO first, then system paths for hybrid MBR - Support three BIOS boot methods: 1. isolinux (if syslinux files present and not on arm64 host) 2. GRUB (using existing eltorito.img/cdboot.img from source ISO) 3. GRUB (generating eltorito.img if i386-pc modules available) Backwards compatibility: - ISOs with syslinux files work unchanged on x86 hosts - Older ISOs with isolinux still produce isolinux-based output ISOs Support matrix: Host | Source ISO | syslinux | GRUB BIOS imgs | Output ISO boots via -------|----------------|----------|----------------|---------------------- amd64 | amd64 (old) | yes | - | isolinux BIOS + EFI amd64 | amd64 (new) | no | yes | GRUB BIOS + EFI amd64 | amd64 (new) | no | no | GRUB BIOS + EFI (generated) amd64 | arm64 | no | no | EFI-only arm64 | amd64 (old) | yes | yes | GRUB BIOS + EFI (from ISO) arm64 | amd64 (old) | yes | no | EFI-only (warning) arm64 | amd64 (new) | no | yes | GRUB BIOS + EFI (from ISO) arm64 | amd64 (new) | no | no | EFI-only (warning) arm64 | arm64 | no | no | EFI-only Note: "GRUB BIOS imgs" means eltorito.img or cdboot.img + boot.img in ISO See grml/grml-live#483

xorriso is required for GRUB-based and UEFI boot support added recently, making the mkisofs/genisoimage fallback paths largely non-functional. Simplify by requiring xorriso unconditionally.

xorriso 1.1.6 is ancient (2011), so no need to check for it any longer. This also allows us to drop the check on UEFI_ENABLE, which is no longer needed.

- Remove duplicate VERSION in param loop - Remove extra closing brace in fold marker - Remove now redundant "Using xorriso" output - Remove redundant USE_GRUB=false assignment after it's no longer used - Remove unused ADD_OPTS variable - Replace $(($OPTIND - 1)) spacing with $(( OPTIND - 1 )) - Replace [ -e X -a ! -n Y ] and [ ! -z X ] with modern equivalents - Replace [ ! -n ] with [ -z ] - Replace `which` with `command -v` - Update Grml ISO name (having also new file naming schema)

The MirBSD-derived mbrldr/mbrmgr binaries offer no functional advantage over the syslinux MBR. Replace them with automatic syslinux MBR discovery (checking the same paths previously used by --syslinux-mbr), removing the need for a bundled MBR binary. FTR: - Remove mbr directory - Always use syslinux MBR when bootloader is syslinux - Remove ismirbsdmbr logic from install_mbr, always use the standard active partition flag (0x80) - Deprecate --syslinux-mbr and --mbr-menu as no-ops with warnings to preserve backwards compatibility - Update debian + tarball.sh files accordingly

zeha · 2026-03-13T09:07:34Z

Not sure what to do about the DOS/MBR boot sector; partition 1 issue or whether it's really blockdev --rereadpt /dev/loop0 that's failing GitHub actions :-/

yeah I was wondering if that is a real or an unrelated failure. It might mean the partition 1 is not marked correctly in the partition table, or something else goes wrong.

I looked at this yesterday and that resulted in #102. The file command is sensitive to the actual MBR code (!).

mika · 2026-03-13T09:12:19Z

We're continuing with this one in #104 now to keep things together

mika requested review from jkirk and zeha March 10, 2026 16:31

zeha reviewed Mar 10, 2026

View reviewed changes

mika force-pushed the mika/483 branch from 42ecf1a to 2a3fc9b Compare March 10, 2026 16:57

mika force-pushed the mika/483 branch from 2a3fc9b to b7b321a Compare March 10, 2026 17:10

mika requested a review from zeha March 10, 2026 17:22

mika mentioned this pull request Mar 10, 2026

Support GRUB 2 BIOS + replace mbrldr/mbrmgr with syslinux MBR #99

Closed

mika added 6 commits March 13, 2026 08:47

grml2iso: drop mkisofs/genisoimage support, require xorriso

a8470ad

xorriso is required for GRUB-based and UEFI boot support added recently, making the mkisofs/genisoimage fallback paths largely non-functional. Simplify by requiring xorriso unconditionally.

grml2iso: drop xorriso version check

28481c2

xorriso 1.1.6 is ancient (2011), so no need to check for it any longer. This also allows us to drop the check on UEFI_ENABLE, which is no longer needed.

mika force-pushed the mika/483 branch from b7b321a to 3d8142d Compare March 13, 2026 07:48

mika closed this Mar 13, 2026

mika mentioned this pull request Mar 13, 2026

Support GRUB 2 BIOS + replace mbrldr/mbrmgr with syslinux MBR #104

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mika deleted the mika/483 branch March 13, 2026 09:17

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mika commented Mar 13, 2026 •

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