Post History

How to add a file to a >5GB bootable UDF ISO?

I have a moderately large ISO image (>5 GB)[^1] to which I want to add a single file[^2], and I want to do that on Linux (preferably using only software which is available in Debian's *main* and *contrib* sections). I also need to do so without breaking the bootability of the image.

After a lot of web searching, I found out that `xorriso` should be able to do exactly that, using either its `-add` or `-map` commands in combination with `-dev` or `-indev` to start from the existing ISO image, and I eventually settled on:

    $ xorriso -dev ./original.iso -update autounattend_specific.xml autounattend.xml -outdev /tmp/modified.iso -commit

This appears to successfully read the original ISO:

    Drive current: -dev './original.iso'
    Media current: stdio file, overwriteable
    Media status : is written , is appendable
    Boot record  : El Torito
    Media summary: 1 session, 2852630 data blocks, 5572m data, 4091g free
    Volume id    : 'CCCOMA_X64FRE_EN-US_DV9'

It also reports that the file is added, but then:

    Drive current: -outdev '/tmp/modified.iso'
    Media current: stdio file, overwriteable
    Media status : is blank
    Media summary: 0 sessions, 0 data blocks, 0 data, 15.5g free

and the output file created becomes 458752 bytes, which is clearly nowhere near large enough to contain the more than 5 GB of data from the original image. `xorriso` does note some issues relating to El-Torito and warns about them, but I get the feeling that my current problems aren't even related to that.

I do strongly suspect that I'm missing something, and that it's probably something obvious; but what?

More generally: **On Linux, how do I add a file to a bootable UDF ISO image and get a complete image file as output, while keeping the resulting image bootable?**


 [^1]: Specifically a Microsoft Windows 11 installation DVD image
 [^2]: Specifically the `autounattend.xml` file to automate installation