C-Command Software Forum

Images still read-only after converting ISO files to DMG (RW) format

I’m trying to burn an ISO image with a small change by converting it to a read/write DMG image. However, the DMG files that DropDMG creates by converting an ISO file are always read-only, even when the format is set to “.dmg (RW)” in configuration. Am I missing something, or is it not possible to create a writable DMG from an ISO file?


The filesystem on an ISO image is read-only. When DropDMG converts the image to read-write .dmg format, it creates a read-write image with the same read-only filesystem. In other words, converting changes the format of the .dmg container, but it doesn’t change the filesystem. Sorry, that’s just how OS X’s imaging engine works.

A workaround is to mount the ISO image. Then drag the mounted icon from the desktop onto DropDMG. Then it will create a new read-write .dmg image with a Mac filesystem. You can then make your changes and burn the .dmg image using DropDMG. You would have to use “hdiutil makehybrid” if you need to get the image back to ISO format, however.

Thanks, this explains the behavior I was seeing. Would the workaround you suggested preserve a bootable ISO image?

I think so, although I haven’t tried it.