1. Mount CentOS/RHEL 6.9 installation iso into /media/RHEL6.9;
# mkdir /media/RHEL6.9 # mount -o ro /dev/cdrom /media/RHEL6.9
2. Create a new folder /opt/make_iso;
# mkdir /opt/make_iso
3. Copy all files of CentOS/RHEL 6.9 installation iso to /opt/make_iso;
# tar cf - /media/RHEL6.9 | ( cd /opt/make_iso/; tar xpvf - )
4. Copy uefi kickstart config file to the root directory of iso image:
# cp uefi_ks.cfg /opt/make_iso/ks.cfg
5. Copy efiboot.img to the root directory of iso image:
# cp /opt/make_iso/images/efiboot.img /opt/make_iso
6. Run below command to generate UEFI bootable iso image:
# mkisofs -b isolinux/isolinux.bin -no-emul-boot -boot-load-size 4 -boot-info-table -eltorito-alt-boot -e efiboot.img -no-emul-boot -no-iso-translate -r -l -T -J -o /tmp/uefi_boot.iso /opt/make_iso
File /tmp/uefi_boot.iso is the UEFI-bootable ISO image.