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?

posted 6 months ago

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Canina‭

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