C-Command Software Forum

Converted DMG cannot be opened - DiskImageMounter: legacy image should be converted


i have here a DMG which i created with DropDMG yesterday. Now we need to replace the layout due to some last minute changes.
So i´ve converted the DMG using DropDMG. The new DMG is created, but cannot be mounted. I get the error: … - legacy image should be converted.

Any idea what could have gone wrong? Am i missing something?


That doesn’t make sense to me because, unless you were using a very old version of macOS to create the .dmg, a disk image should only be considered legacy if it was created more than 10 years ago. Such images need to be converted (to the same format, if you want) in order to update their internal structure. I can look into this more if you want to send in the original disk image file and screenshots showing what you did with it that caused the error.

However, if your goal is to update the layout, it’s probably better to just copy the files in the old disk image to a folder and create a new disk image from it with the new layout. Converting doesn’t change an existing layout, anyway—it only affects the compression/encryption/license of the disk image wrapper.

Thanks for replying.

The Mac on which i created the original DMG and did the conversion is running Mac OS 14.4.
I thought doing a conversion is the easiest and fastest way. :wink:

The DMG i wanted to convert with the new layout was signed and contained a notarized app. Is it possible that that caused it?

But anyway, i will create the DMG from scratch.



I don’t think so, as that’s normal for disk images these days. It’s possibly that there was some other fluke occurrence that caused DiskImageMounter to report the wrong error message.

Seems that i have to do the whole notarization process again: Create signed dmg, add app to it and upload dmg for notarization.

Becaue, when i create a DMG and add the notarized app to it, then i have to notarize the DMG again. At least i cannot staple the previous ID to the new DMG.

But maybe i am missing something about the whole notarizing process.

That sounds correct. I think you can either notarize the app itself (with Xcode) before making the .dmg or notarize the .dmg and staple it (without changing the .dmg).