Disk Utility: Operation failed: error 432534

We really can't help with the information you have provided. Please let us know the exact set of steps you are using in Disk Utility for the intended result. Why are you converting a .dmg file to an .iso file? I don't believe you can do such a conversion using Disk Utility. You will need to find a third-party utility that can convert .dmg files to .iso files. As an example, Roxio's Toast should fit the bill but I'm sure there are others. You can search the App Store or MacUpdate.

I've used Etcher to burn the "BaseSystem.dmg" file contained within the macOS installers to USB and it boots just fine since this image file does contain the necessary blessed Apple bootloader. Of course the bootloader & version of macOS on this particular .dmg image is not your typical macOS boot process since it creates multiple virtual drives as it boots so data can be written to various locations macOS expects. There is no way to know if the file the OP is trying to use is any good or if it is even bootable and if it is bootable does it contain the boot files which will create virtual RAM disks.

FYI, To "burn" the .dmg file to USB with Windows or Linux first requires uncompressing the .dmg file and using the uncompressed image as a source for Etcher or "dd". AFAIK a .dmg file is just a raw disk image very much like many .iso files (of course there can be some differences as well). Apple's .dmg version adds in image compression.

I have seen methods to create a bootable USB drive from the original Snow Leopard DVDs, but I've never personally tried it or what is actually involved to make it. There are (or were) numerous websites or posting with instructions years ago. That would be the safer to way go if El Capitan is not an option for the computer.

No Windows machine can read them without added software to read Mac formats. But if you have a Mac, then there is no need to convert it to an .ISO. The Windows software to read Mac disks is called MacDrive. But I don't know if it is able to read disk images.

Don't know. Do you not have access to a Mac? What is on the disk image?

Kappy wrote:

We really can't help with the information you have provided. Please let us know the exact set of steps you are using in Disk Utility for the intended result. Why are you converting a .dmg file to an .iso file? I don't believe you can do such a conversion using Disk Utility. You will need to find a third-party utility that can convert .dmg files to .iso files. As an example, Roxio's Toast should fit the bill but I'm sure there are others. You can search the App Store or MacUpdate.

I know that "hdiutil" will convert a .dmg file to an .iso file, but requires using the Terminal command line.

However, trying to get a macOS image to boot is another matter. If the .dmg file the OP has is a bootable image, then the .dmg file can be used as a source for Etcher to "burn" it to a USB drive. Etcher must be run on macOS 10.10+.

My concern is where this Snow Leopard image came from as it could be damaged or could even contain malware since Apple only ever released Snow Leopard on DVD.

I don't know what is an image of, so I did ask above. You cannot boot from a .dmg file even if it has a bootable system because on startup the OS has to write to the startup disk. Disk image files are not writeable, hence you cannot boot from one. However, you can restore the image to a properly formatted disk. Of course, the computer in use would have to be old enough to be started from a Snow Leopard system. So, that sort of limits it to Macs from Mid-2011 and earlier depending on the version of Snow Leopard on the disk image.

Converting it to a .ISO image may not do much good because the files on the .dmg may not all show up on a .iso as they were on the .dmg. I think the OP needs to find a Mac in order to use the .dmg.

I think the Etcher expects to work with a .iso file, not a .dmg file unless you know otherwise. I've only used to work with Linux distros, and it doesn't always work with them.

Parallels will work with either .iso or .dmg files to create a VM, so it would work with the .dmg to make a VM of Snow Leopard.

The old OS X distributions consisted of a separate .dmg file within the distribution .dmg. One only needed to select the main image and CTRL- or RIGHT-click on it and select Show Package Contents from the context menu. Open the Contents folder, open the SharedSupport folder inside of which you will find the InstallESD.dmg image. Use Disk Utility to make a clone/copy of InstallESD.dmg to a formatted USB flash drive. Voila! That is it. Much easier than the hoop-jumping that's now needed but at least Apple provided a mechanism to do it. Before macOS there was no provision for doing this that came from Apple.