Trying to add a single file to an existing ISO I ran into a bit of hiccup I can't see through. Here it is:

Having never done it before but encouraged by reading the advice from this question: Add/Delete/Modify files within a Disk Image (.dmg)?

I ran:

hdiutil convert -format UDRW -o EditableImage.dmg givenImage.ISO

and although it created a DMG that was was "mount-able" - I was not able to edit it in any way. Trying to run

hdiutil resize -size 400m EditableImage.dmg

gave me a failure with Resource temporarily unavailable. (I rebooted just to be sure there was nothing using it)


hdiutil imageinfo EditableImage.dmg 

indicated it was of Format: UDRW

but I couldn't actually write to it.. and this led me to asking here the question: what am I doing wrong?
[Runnning Catalina on a less than 1 yr old Mac with all updates]

  • Please add the output of hdiutil imageinfo filename.iso to your question, or post it to e.g. https://paste.ee and provide the link. Dec 23, 2020 at 14:52

1 Answer 1


This might help people who are still running into this issue. In my case, the DMG was mounted which gave the error "Resource temporarily unavailable", when I tried to use "hdiutil convert" on it. So, after simply ejecting it, the error went away, and I could use the command with no issues.

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