C-Command Software Forum

Mounted DMG doesn’t grow in size automatically

I wanted to copy files into a mounted dmg but get always the error message that there is not enough space.
I thought I could use a mounted dmg like a normal drive adding (as well as deleting) files.

Are my settings wrong?

(I created a “.dmg Read-write (can be modified)”, use a passphrase to encrypt it; I use 10.5.2)



Each .dmg has a fixed capacity. With DropDMG, this is based on the size of the file/folder that you drop onto it. It will typically create the .dmg large enough to hold the source items, with a little bit of extra space so that you can add a background image or other small files. A future version of DropDMG will let you create a blank .dmg with a capacity that you choose. For now, you would need to do that using Disk Utility.

Michael, thank you very much for your quick reply.
Now I think I understand how it works.
I could create a dmg with – let’s say – a 500MB-file, delete this after the dmg was created and use the space to copy into the dmg as many files as I wanted to as long as their total sum doesn’t exceed 500 MB.
Is this right?
(If dmgdrop works this way then it would be fine with me!)


Thanks again :slight_smile:

Hi Michael, Any update on this feature? I am interested in this and in a related feature, which is the ability to simply resize an existing dmg. (I couldn’t find any information on resizing dmgs in the help, so I assume this feature isn’t implemented.) I know this can be done via command line. I just downloaded DropDMG and was hoping this cute little program could take care of my other DMG needs as well. Thanks!

It will be in DropDMG 3.0, which will be a free update for those who purchase DropDMG 2.8.5 today.

What are you trying to do, exactly? The hdiutil tool does have a resize command, but I haven’t found it particularly useful.

Oh goodie! Glad to hear it’s still planned and that there’s no reason to wait. Thanks.

I have a DMG that I want to add a number of files to, though the size is unknown as of right now. I was going to make the DMG large and then shrink it down once I am finished fiddling with it. I am a recent Mac convert from Linux, so I can rock the command line a little better than I care to talk about. I just don’t know the Mac specific commands (eg hdiutil) very well and was trying to avoid a visit to the man pages. Cheers!

OK, that is a case where the resize command would be useful. Another, perhaps easier, option would be to create a sparse image (so that the logical size can be large, while the physical size on disk only increases as-needed). DropDMG doesn’t currently support creating sparse images; that will also be added in 3.0.

DropDMG 3.0 is now available and includes the ability to create new blank disk images.

Great! Thanks.