How do I create a DMG file on linux Ubuntu for MacOS

There are several ways that this can be accomplished under Ubuntu and I describe here one technique that I have tested on Ubuntu 18.04 and also tested the resulting dmg file on a colleague's MacOS computer. Out of the several techniques that have been suggested online I believe this one is the better choice!

There are only a few relatively straightforward steps to follow:

1. Install some applications: First you will need to install hfsprogs which is a port of Apple's Open Source tools for HFS+ filesystems:

   sudo apt-get install hfsprogs
   

   This will provide the necessary tool to work with Apple's HFS+ filesystem.

2. Create the HFS+ file: Next you will create a 16MB dmg file and format it to HFS+ wih the following two command lines:

   dd if=/dev/zero of=/tmp/my_application.dmg bs=1M count=16 status=progress
   mkfs.hfsplus -v Install /tmp/my_application.dmg
   

   There are a few variables here which you should look at: you can alter the count=16 to reflect the size dmg file that you need and you can alter the volume label, given here as -v Install.

3. Mount the file, copy your program: Now you can create a mount point, mount your dmg file there, copy your program files to the mounted dmg files and then unmount it all:

   mkdir -pv /mnt/tmp
   sudo mount -o loop /tmp/my_application.dmg /mnt/tmp
   sudo cp -av my_program /mnt/tmp
   sudo umount /mnt/tmp
   

   The variable to alter here is of course the actual name of your application in the cp command which I have given above simply as my_program.

Now your completed dmg file is sitting in /tmp/my_application.dmg ready for deployment and testing on MacOS!

References:

• How to build a dmg Mac OS X file (on a non-Mac platform)? A coverage of some of the different techniques to create a working dmg file.