I am using grub-mkrescue and xorriso to create a bootable Linux ISO and facing some issues.
Please suggest what i might be doing wrong or missing. (The reason i need to create a bootable
ISO is that the application i am using is based of an old Debian version and it provides a .img
containing the vmlinuz, initrd and root filesystem including the application binaries. I need to
create the ISO to deploy the application in the cloud as a cloud instance)

I am following 2 step process:

Step1: grub-mkrescue

        sudo grub-mkrescue --modules ="part_msdos, part_gpt, gzio, ext2, iso9660" -o final.iso -d img0

img0 is my working folder.

Step2: xorriso
sudo xorriso -as mkisofs -c boot.catalog -volid “MY_CUSTOM_LINUX” -eltorito-boot boot/grub/i386-pc/eltorito.img -no-emul-boot -boot-load-size 4 -boot-info-table -isohybrid-mbr /usr/lib/ISOLINUX/isohdpfx.bin -partition-offset -append_partition 2 0x83 disk.img -output final.iso -partition_cycl_align out-combine

I copy the contents of step1 to out-combine my second working folder. out-combine is where I have the vmlinuz (debian linux), initrd, grub.cfg.

disk.img is an ext2 partition I created with the intention of using it as my root file system.

The problem I am facing. when i boot the ISO in virtual box, grub comes up with the following filesystems:

(hd0), (cd), (cd,msdos2) (cd,msdos1)

Only the filesystem type for (cd) is recognized.
Since the filesystem (cd,msdos*) is not recognized, root filesystem type is not known, grub is unable to load linux and initrd. I don’t understand why it makes msdos1 a partition under cd rather than hd0.

also, when i run fdisk on the resulting iso, i get the output:

Device Boot Start End Sectors Size Id Type
final.iso1 * 64 61439 61376 30M 17 Hidden HPFS/NTFS
final.iso2 61440 2158591 2097152 1G 83 Linux

Just for comparison, i downloaded a pre-built Debian linux ISO, booted in Virtual box as a VM and checked the grub prompt and find the filesystems

(hd0), (hd0,msods5), (hd0,msdos1)

(hd0,msdos1) is recognized as an ext* filesystem.

Please help.

I downloaded debian linux pre-built iso and booted it in Virtual box for comparison.