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As the title says I would like to know how the guys at Canonical generate the release ISO file for this version of the Ubuntu OS. Above all I'm interested in how they create the isohybrid image.

How can I replicate the process starting from the files contained in the ISO file? Cleary the derived image should be bootable in EFI/UEFI based systems.

Also, I would like to know why, when I try to display the partition contents of the ISO image with fdisk, one of the two partitions (the first one) its type is "Empty" when it contains all the Ubuntu files for the install media, isn't it a ISO9660 like partition?

I would also be interested in replicating the partition structure of the ISO file on a USB drive.

Could someone point me in the right direction?

Are the answers to my questions documented somewhere? Or at least some?

Thank you very much!

digitalboy
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  • Voted to close as IMO the question is too broad. There are several components to building an iso. See http://live.debian.net/manual/3.x/html/live-manual/index.en.html . From there you need to understand the various components. See https://help.ubuntu.com/community/LiveCDCustomizationFromScratch . Understand how each tool works (squashfs, mkiso, boot process - https://help.ubuntu.com/community/LiveCDCustomizationFromScratch#Make_a_bootable_USB_image ) – Panther Sep 15 '15 at 19:57

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Thank you for the suggestions guys but I think I've found the answer to my own question, also it was (at least partially) answered here: How do I create an EFI-bootable ISO of a customized version of Ubuntu? in great detail, with the exception of the isohybrid portion.

In fact that guide produce a bootable ISO9660 (Rock Ridge) EFI/UEFI image but when I try to write the resulting image to a USB drive with the low level dd utility all I get is an unbootable drive (it works however when I burn it to a DVD)

The trick here is to use the isohybrid utility to modify the image: isohybrid --uefi output.iso, this will add a small FAT partition to the structure of the ISO image, making it capable of booting via USB on EFI/UEFI systems.

digitalboy
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