C-Command Software Forum

Can't create a read only .dmg disk image

I set up a configuration for a read only .dmg disk image without compression. But when I try to create a new blank disk image using that configuration, I can only choose a read/write, sparse disk, or sparse bundle disk image. How do I create a new blank disk image that is read only (so I can use Verify) and that has a fixed size that I designate? Thank you.
I am using Mac running 11.5.2.

Could you explain more about what you are trying to do? DropDMG doesn’t let you create a read-only blank disk image because you would not be able to add anything to it (since it’s read-only). If you want to be able to Verify Image…, could either create a read-only disk image from a folder or create a read-write blank disk image, add your files, and then convert it to read-only.

Yes, that makes sense. Both of the options you mention could work for what I want to do (have encrypted files that have their integrity tested). I just created one from a folder, and when I opened it, it verified it, so I must have succeeded in making it read only. I have another question now. I understand it can only verify a read only disk image. But what about in the case of an Eaglefiler library? Those are effectively read/write, and have a checksum run on them, don’t they? Is that different from Verify Image? If I have a group of files that I want to encrypt, is it better to use a DropDMG disk image, or an encrypted Eaglefiler library? The latter allows me to add and delete while still allowing checksums, doesn’t it? Sometimes read only is fine, but sometimes it would be nice to be able to add and delete. Thanks again.

Yes, it’s different. A read-only disk image stores a single checksum (in the disk image) for the entire contents of the image. An EagleFiler library stores checksums (in the .eflibrary file) for each file in the library. These are verified using the Verify command in EagleFiler, not via DropDMG.

If you want to add or delete, EagleFiler is much easier. Even if not, having per-file checksums is nice because in the event of damage you can easily see which files are damaged and which are OK, rather than just knowing there was a failure “somewhere.” On the other hand, it’s fewer steps to batch verify a bunch of encrypted .dmg files.

OK, that is good to know. Is there a way to encrypt an Eaglefiler library that didn’t start out that way, or is it better to just create a new encrypted library and move my files in to it from the unencrypted one? Thanks!

You could use DropDMG to create an encrypted blank disk image and move the whole EagleFiler library folder into it.

Thank you. How do I move an encrypted disk image from one computer to another? When I try to copy it to a usb drive, it either copies the files unencrypted, or just copies an alias for the disk image, that does nothing. What should I be doing? Thanks.

It sounds like you are dragging the mounted volume. First, eject it. Then drag the .dmg file.

Yes, thank you; that worked.

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