Instructions: Create a .dmg from an .app file on the Mac

Convert .app to .dmg

This is again a manual that I just had to collect myself in an English forum. The reason why I want to turn an .app into a .dmg file is as follows: If you try to copy a macOS installer to a friend over the Internet because he needs it for an old Mac, you have the problem that this is over Dropbox or FTP is not working properly. This is because an .app file on the Mac is actually not a single file, but a folder with many files it contains. The Finder only shows the folder as a file with the extension .app - provided that the file extensions have been shown.

If you copy an .app file into the Dropbox or via FTP to a server, it happens, for example, that Dropbox displays a file that is 0 KB in size. Virtually nothing has been loaded from the installer, just a faulty file that has no content.

On the other hand, on a server that is supplied with the installer file via FTP, one has the problem that a folder with a lot of content is displayed and the acquaintance cannot simply download a single file. So this path is not expedient either.

Converting an app file into a DMG image - helpful and quite easy to do.

Converting an app file into a DMG image - helpful and quite easy to do.

My first detour: create a zip archive

For the last few months I have always solved this problem by making a ZIP file from the macOS Installer.app. However, due to the size of the file, this takes a long time and I often got the feedback that the other person could not load the file completely because it was supposedly incomplete. But even if the transfer works: A macOS installer is around 5 to 10 GB and unzipping a file of this size is a real challenge for older Macs.

A problem that occurs more often when you have loaded huge zip files: The browser refuses to cooperate (thanks to Stefan for the screenshot).

A problem that occurs more often when you have loaded huge zip files: The browser refuses to cooperate (thanks to Stefan for the screenshot).

The best way: create a DMG image

Only today did I get the idea to see if the Installer.app could not be turned into a .dmg file, because DMGs are used as the method of choice for almost all software downloads for Macs, if you Want to make apps available on the Internet.

Instructions in short form:

  1. Create and name folders in the Finder
  2. Drag the app file into the folder
  3. Open Disk Utility
  4. Under File> New Image> Image from Folder choose
  5. Select the folder with the app file
  6. Create image using the "Save" button
With the hard disk service program you can create a DMG file on the Mac using the command "Image from folder".

With the hard disk service program you can create a DMG file on the Mac using the command "Image from folder".

More features for stylish folders

If you want to spruce up the folder view of the DMG archive a bit, you can, for example, copy an alias of the programs folder so that users can put an app directly into the program folder.

The appearance of the folder can be set using the display options.

The appearance of the folder can be set using the display options.

For further options you can either use the gear symbol at the top of the folder's menu bar or the Finder menu "View".

The "Display options" window can be displayed using the gear symbol. With this you can set the font size, the folder background, the icon size and much more for the corresponding folder.

Here you can see the alias of the programs folder, as well as the options for hiding the sidebar and showing the display options. For me it says "hide" because the window was already shown.

Here you can see the alias of the programs folder, as well as the options for hiding the sidebar and showing the display options. For me it says "hide" because the window was already shown.

If you also want to hide the sidebar in the folder, click on the folder window and go to the "View" menu in the Finder and find the item "Hide sidebar" there. All things that you do with the folder are also backed up with the creation of the DMG file.

Success message: We now have the DMG image for the Mojave installer in our pocket or on the disk.

Success message: We now have the DMG image for the Mojave installer in our pocket or on the disk.

The advantages of the DMG format

Creating the image took a good 2018 to 10 minutes even on my MacBook Pro 15, but opening the DMG archive takes seconds and hardly requires any computing power. In addition, the DMG files can be easily exchanged via cloud services such as Dropbox, OneDrive or similar. Even shipping with Droppy.ch, FileMail or wetransfer is not a problem if you do not exceed the maximum file size.

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8 comments

  1. Beatrix Willius says:

    So this is how it works by hand. DropDMG (https://c-command.com/dropdmg/) or DMGCanvas (https://www.araelium.com/dmgcanvas) cost a little money. But creating a DMG file is a bit more comfortable.

    • Sir Apfelot says:

      Hello Beatrix! You always have good additions. Thanks for that! : D
      I don't need any software for the three clicks, but doing it more often would be a good investment.
      LG!

  2. Michael says:

    Hi, I recently noticed that you can also create a USB installation disk with a few commands that you can find in Apple Support when you search for "Create installation medium". All you have to do is load the desired OSX version in the app store and the .app file is converted accordingly. In my opinion the best solution because downloading the files with any other operating system and creating an installation disk turned out to be very difficult.

    • Sir Apfelot says:

      Hi Michael! Yes, thank you for your hint! I think there is already a post on the blog. Anyway, it sounds kind of familiar to me. : D

  3. Jojo says:

    "Creating the image took a good 2018 to 10 minutes even on my MacBook Pro 15 ..."

    But I'm a bit surprised. On my 2014 MacBook Pro, converting Majave took exactly 9 minutes.

    Question:
    By default, the image format in the "Save As" dialog is "Compressed". If you change that to "read only", the conversion only takes 7 minutes.
    Does anyone know the consequences of "read only"?

  4. Jojo says:

    OK, just found out for myself. Apple has z. Sometimes really good documentaries:

    "Read only: The image file is write-protected and faster to create and open."

    "Compressed: The data is compressed so that the image file is smaller than the original data. The image file is write-protected."

    Compressing an .app file is of course pointless. You can tell that afterwards the size of the .dmg file is exactly the same as the .app file.

    • Sir Apfelot says:

      Hello Jojo! Thanks for your advice. This is a good addition to the article! I don't know why it took so long on my MacBook Pro 2017. Maybe I shouldn't have done so much on the side. : D

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