Modifying A Netinstall ISO Image

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I want to make a very minor change to the netinstall ISO image, namely adding a few parameters to the boot line to automatically kick off a kickstart installation. Here is my approach:

mount -o loop CentOS-6.2-i386-netinstall.iso /mnt
cp -pr /mnt /tmp
cd /tmp/mnt
vi isolinux/isolinux.cfg # Add some stuff to the default append line and reduce timeout
mkisofs -o /tmp/CentOS-6.2-i386-netinstall-ks.iso -b isolinux/isolinux.bin -c isolinux/ -no-emul-boot -boot-load-size 4 -boot-info-table -R -J -v -T .

I got the mkisofs command line from (I couldn’t find anything similar in the CentOS/RHEL 6.X documentation).

This appears to work just fine, but the resulting ISO image is about 20% bigger (194M vs. 162M) and has an extra TRANS.TBL file at the top level. Any ideas what is causing this? It’s no big deal as I’ve got things working, but I’m curious nonetheless…


4 thoughts on - Modifying A Netinstall ISO Image

  • Hello Alfred,

    man mkisofs should give you an explanation of the used options. The directory record options used (-J, -R and -T) probably increase the ISO
    size compared to when those aren’t used.

    Regards, Leonard.

  • And that is just about the size of the duplicate initrd.img file.

    If you are going to ignore the manual page you posted and include the images directory, hard link the duplicate file and re-author :)


  • Good point, but since I don’t know how the original ISO image was created, I used this command which I found in the CentOS/Red Hat documentation (I
    assumed that a similar command was used to create the original ISO image).


  • Good catch!

    Yes, it does say that you only need to copy the isolinux directory, and that appears to work and make the ISO image much smaller to boot! So no rescue mode, but that’s OK with me as I only need it to start a network kickstart installation.