...
sudo mkisofs -q -disable-deep-relocation -rational-rock -cache-inodes -joliet -full-iso9660-filenames -no-emul-boot -boot-load-size 4 -boot-info-table -e
ltorito-boot isolinux/isolinux.bin -eltorito-catalog isolinux/boot.cat -o ubuntu-pre.iso preseed_ubuntu
We use debian-installer preseed to achieve no-attended installation.