The issue is that configfile ${cmdpath}/grub.cfg doesn't work since $cmdpath is (cd0)/EFI/Boot.

configfile (cd0)/EFI/Boot/grub.cfg

doesn't work,
while

configfile (cd0)/EFI/BOOT/grub.cfg

works.

P.S. Sorry, I made a copy-paste fail in the "steps to reproduce", the directory should be "isoroot/EFI/BOOT" in all occurrences.

When booting GRUB standalone (created following https://wiki.archlinux.org/title/GRUB/Tips_and_tricks#GRUB_standalone ) from an optical disc (an emulated one using IODD 2531), where it was placed at /EFI/BOOT/BOOTx64.EFI in both the ISO9660 and in an attached FAT image used as an EFI system partition, GRUB's $cmdpath was wrong. echo $cmdpath returned (cd0)/EFI/Boot. Notice that it's Boot not BOOT, but ls (cd0)/EFI/ showed that the directory is indeed called BOOT.

This only happens on my HP ProBook 450 G2 laptop. I can't reproduce it on another PC I own nor on the same laptop when the ISO is written to a USB flash drive.


OS: Arch Linux
Package versions:
grub 2:2.06.r261.g2f4430cc0-1
libisoburn 1.5.4-2
dosfstools 4.2-2
mtools 1:4.0.40-1


Steps to reproduce:

$ mkdir -p isoroot/BOOT/EFI

$ echo 'configfile ${cmdpath}/grub.cfg' > grub-embed.cfg

$ cat <<'EOF' > isoroot/BOOT/EFI/grub.cfg
insmod part_gpt
insmod part_msdos
insmod fat
insmod iso9660
insmod all_video
insmod font
if loadfont "${prefix}/fonts/unicode.pf2" ; then
    insmod gfxterm
    set gfxmode="auto"
    terminal_input console
    terminal_output gfxterm
fi

menuentry 'UEFI Firmware Settings' --id 'uefi-firmware' {
    fwsetup
}

menuentry "System shutdown" --class shutdown --class poweroff {
    echo "System shutting down..."
    halt
}

menuentry "System restart" --class reboot --class restart {
    echo "System rebooting..."
    reboot
}
EOF

$ grub-mkstandalone -O x86_64-efi \
        --modules="part_gpt part_msdos fat iso9660" \
        --locales="en@quot" \
        --themes="" \
        -o "isoroot/BOOT/EFI/BOOTx64.EFI" \
        "boot/grub/grub.cfg=grub-embed.cfg"

$ mkfs.fat -C efiboot.img 8192

$ mmd -i efiboot.img ::/EFI ::/EFI/BOOT

$ mcopy -i efiboot.img isoroot/BOOT/EFI/BOOTx64.EFI isoroot/BOOT/EFI/grub.cfg ::/EFI/BOOT/

$ xorriso -as mkisofs \
        -iso-level 3 \
        -full-iso9660-filenames \
        -joliet \
        -joliet-long \
        -rational-rock \
        -partition_offset 16 \
        -append_partition 2 0xef efiboot.img \
        -eltorito-alt-boot \
        -e '--interval:appended_partition_2:all::' \
        -no-emul-boot \
        -isohybrid-gpt-basdat \
        -output "grub-boot-test.iso" \
        isoroot/

Burn and boot grub-boot-test.iso.

archiso issue: https://gitlab.archlinux.org/archlinux/archiso/-/issues/183 . Currently archiso uses the following embeded grub configuration file to work around it:

if ! [ -d "$cmdpath" ]; then
    if regexp --set=1:isodevice '^(\([^)]+\))\/?[Ee][Ff][Ii]\/[Bb][Oo][Oo][Tt]\/?$' "$cmdpath"; then
        cmdpath="${isodevice}/EFI/BOOT"
    fi
fi
configfile "${cmdpath}/grub.cfg"