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I'm trying to add a file to an ISO then reburn it. In Disk Utility, I mount the original ISO, choose "Create From ..." to create a new image file with "read/write" access and save it. When I mount the new image file, it's read-only and I can't change it or add files.

What am I doing wrong? Why can't I mount the image with write permissions?

  • Why not copy the files from the iso to a folder, add your new files, then reburn? – David Anderson Mar 5 at 17:11
  • The ISO is bootable. I'm not confident that it would still work when I'm done. The benefit of the ISO is that it keeps the boot information. – user1209675 Mar 5 at 18:03
  • You may have to use the hdiutil command to create the new iso file. Basically, I do not think you can accomplish your task using the Disk Utility application. Do you know how the current iso file is configured to boot? – David Anderson Mar 5 at 18:13
  • Yes, I'm trying to make an ISO for unattended installs of Windows. – user1209675 Mar 5 at 18:47
  • Windows? Why didn't you say? Are you doing a legacy eltorito boot or EFI boot? You can do this using macOS, but would it not be better to do this using Windows? – David Anderson Mar 5 at 18:50
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Let's assume you have a physical or virtual FAT32 or ExFAT formatted drive. You could mount the ISO file and then copy all the files to this drive. I would recommend using the Terminal application to do the copy. Using the Finder application may result in the creation of ._* files. Although these files can be removed by using dot_clean.

To create a legacy bootable ISO file, use the command given below.

hdiutil makehybrid -o windows10.iso /Volumes/ESD-USB -no-emul-boot -boot-load-size 8 -eltorito-boot /Volumes/ESD-USB/boot/etfsboot.com

In this example, the name of the drive shown in the finder was ESD-USB. The -boot-load-size was set to 8 sectors, because the size of the etfsboot.com file was 4096 bytes and the sector size is 512 bytes. ( 8 * 512 = 4096 )

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You cannot modify ISO files using Disk Utility, nor using diskutil on the commandline. This is not built in to those programs.

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