Hi,
are you trying to preseed something?
then just extract a debian standard install disc like netinstall to
/opt/isobuild/debian/image/
do your changes
and the script should rebuild the disk.
unfortunately UEFI only systems wont boot it.
#!/bin/bash
IMAGE=/opt/isobuild/debian/debian-9.3-auto.iso
BUILD=/opt/isobuild/debian/image/
xorriso -as mkisofs \
-r -V "Debian Auto NetInstall" \
-cache-inodes \
-J -l -b isolinux/isolinux.bin \
-c isolinux/boot.cat -no-emul-boot \
-boot-load-size 4 -boot-info-table \
-isohybrid-mbr /opt/isobuild/debian/isohdpfx.bin \
-o $IMAGE $BUILD
Cheers
Markus