Whether it's a mac or Windows computer, the error occurs sometimes and if you are a Mac user, then definitely you should create a bootable macOS USB installer when the Mac failed to work at that point. The solution is to use the macOS bootable USB to install a fresh OS on your Mac. So the question is how to create such a bootable disk on a Windows PC? Honestly, TransMac is a great tool for this but sometimes brings up several issues such as the USB failed to boot. In here, you will get to know about TransMac, the reasons behind the major issues, and the best alternative of TransMac for creating bootable USB from DMG file.

If you see the 'no mountable file systems error' while opening a dmg, here's what you should try: How To Open Dmg File On Mac In most cases, the downloaded dmg file is actually corrupt or had an error downloading. My hunch is that inside that.dmg is a file for which Safari is designated as the default opening/reading app (most likely an HTML or PDF file, although Safari can open numerous different filetypes). I suspect that, on a previous occasion when accessing the contents of that.dmg, somehow you've managed to set one particular file as Safari's. You cannot open disk image file (.dmg) on your Mac and get the “no mountable file systems” error message? ISumsoft BitLocker Reader for Mac can.

About TransMac

TransMac is a very popular application to access DMG volume and make bootable USB from macOS DMG file on Windows. Through this application, the users can easily create a macOS bootable USB on Windows by burning the dmg file to USB. In the past, it is the only application for thoese types of tasks and that's why it is a big name in this industry.

Bootable USB Not Working Created by TransMac?

Like we said above, TransMac is a great Windows tools and helped a lot of Mac users to repair their device by a clean reinstall. However, you might come across issues by your own especially on latest Windows 10 because the software has no update for a long time. The most noticable one is that the USB drive created by TransMac not bootable!

Usually, you will see the USB drive name in startup manager on Mac listed as a bootable device when trying to boot Mac from external drives. Below is an example. The volume labe 'Install macOS Catalina' is the name of USB drive burned from Catalina DMG file. If the USB drive name not showing up, it means the USB drive is not working or bootable.

How to fix 'TransMacBootable USB Not Working' issue? First, make sure the macOS dmg file is downloaded from legal sources. Usually, the dmg file wrapped in a torrent file is not safe and the file is broken sometimes. Here is the detailed tutorial for downloading macOS Big Sur, Catalina or Mojave from legit website.

Secondly, make sure the USB drive is large than 16GB. If not, then the storage is not enough to hold all the installation files from a macOS dmg file.

Thirdly, TransMac is not trial mode. You should purchase a license ($59.95) after the free-to-try period.

From our observation, the issue should be fixed after trying out the above suggestions. If the error pops up again, then it has something wrong with the current OS or potential bugs in TransMac software.And the developers are still working on these issues to fix it asap, but till then you can't stop your work. So, there is a powerful alternative tool that can easily create macOS bootable USB on Windows, called UUByte DMG Editor.

TransMac Not Working? Give a Try on UUByte DMG Editor

UUByte DMG Editor is a great replacement of TransMac when it comes to create a macOS bootable USB. It has a much better user interface and the burning speed is faster than TransMac according to our test. Moreover, through this application, you can extract content from DMG file on Windows OS. The developers have done a great job and made the interface so simple that even a mere novice can easily perform the bootable task. Now, you must be more curious to know about the steps to make macOS bootable USB from dmg file. Here is the details.

Step 1: Prepare for Software Installation

Download and Install UUByte DMG Editor on your Windows computer and for your convenience, the official link is listed above that will help you to get the install file effectively.

Step 2: Connect USB and Import DMG File

Once the installation has been done, launch the application and insert an USB drive into the same computer. On the home page of UUByte DMG Editor, you will get the 'Burn' button, click on it.

Step 3: Settings

Soon, a new window will open and click on the 'Browse' button to load the DMG file stored on this computer. Next to the Browse button, you will find your USB drive and the respected volume label where your USB drive is located.

Step 4: Use Bootable USB Drive

Ensure that the dmg file path is correct and further click on the 'Burn; button. Thereafter, the burning process will start and the progress bar will show the status of the process. The burning process will take a few minutes and once it is completed, you will get a successful message on your computer screen. Now, eject the USB and insert it on your Mac to install the OS from USB drive created by UUByte DMG Editor.

As you can see the steps are so simple and most of the task is performed by UUByte DMG Editor and the only tricky part is to download the DMG file in advance. This application reduces the human effort and stress and gives the utmost result in a short period.

Summary

TransMac is a nice tool to make bootable USB from macOS DMG file on Windows PC. But there are many flaws in TransMac as mentioned above. If the bootable USB not working and this issue could not be fixed, then you can go with UUByte DMG Editor as it has higher success rate and much easy to use. Through this tool, you can save your time and energy.

When you want to install a new app on a Mac, more often than not they will let you download a .dmg file. For a long time, I thought that dmg file is just a special install package, but when working on the post about hiding files on Mac I found out that it is not so simple and I decided to investigate more.

General Information

What DMG stands for?

Dmg Files Not Mounting On Mac

DMG stands for Disk iMaGe. macOS uses them to package multiple files and folders in one container which can be downloaded over the internet. Think of DMG files as virtual disks, they can be mounted and unmounted like any other drive. They do not have auto-run capabilities.

How to open a DMG file?

To start working with a DMG file it needs to be mounted. To mount the disk image double click on the DMG file. Double click on DMG files invokes DiskImageMounter app which is associated with these files by default. Once the image is mounted a new icon will appear on the Desktop.

Another way to mount DMG files is opening them from the Disk Utility in LaunchPad.

If the image contains an app installer you can see its contents by right-clicking on the app icon and selecting “Show Package Contents”.

Are DMG files safe to install?

Since DMG file is a disk image its safety depends on its contents. DMG files are neither safe or unsafe, but they may contain viruses or malware inside. When downloading from the internet always make sure that the web site you are downloading is from a trusted developer.

Downloading a DMG file does not compromise Mac security. To understand this better imaging someone packaged a virus in a compressed file, etc. zip file. Viruses get installed only when the container gets executed.

Downloading viruses or malware over the internet on the computer or copying files from one folder to another does not make any harm.

For instance, if you want to download Flash Player or QuickBooks from the internet go to their original web sites: Adobe and Intuit. Do not download software from unknown web sites.

How to check DMG files for a virus?

If you don’t have an antivirus installed on your Mac, you can try the site called Virus Total. The site was developed by a Spanish company, but later it was acquired by Google. It is totally free.

When a file is uploaded to the Virus Total it runs a number of different antivirus applications and prints the results of the scanning.

For instance, when I was working on my article See How Easy Is To Format External Hard Drive For Mac And PC I was able to identify that Minitool DMG contained a malware.

Is there a fake Adobe Flash Player?

I’ve seen many forum posts about fake Flash Players that install malware on Macs. The way they get installed is the web site pops up a warning message “Adobe Flash Player on your computer is outdated” and they provide a link to an updated version or immediately download Flash Player DMG on your Mac.

When this happens, Force Quit the browser and then delete the DMG file from the Downloads folder.

Flash Player (or any other app) will not install if DMG is not mounted and the installer app is not started.

Where do DMG files go?

When downloading DMG files go to the current user Downloads folder by default. However, the browsers may have other folders configured as Downloads, so if the browser didn’t download in the default folder check the browser settings.

If you can’t find the file, learn how to find files here. Just search for files with dmg extension.

When user double clicks on the DMG file the drive mounts and can be accessed either on the Desktop or from a sidebar in the Finder. If the drive is not visible in the Finder go to Finder’s Preferences and enable External disks box under Locations in the Sidebar tab.

Working with DMG files

How to create a DMG file

Anyone who has a Mac can create a DMG file using Disk Utility. With Disk Utility you have options to create a black image or an image from an existing folder. There is a number of things that can be configured for a blank disk image: size, file format, encryption method, partition type, and disk image format.

Let’s review some of the options:

Size: the maximum size of the disk image. Once the disk image is created its size can be changed with Resize option in the Disk Utility.

Format: Use the following rules when deciding which format type to choose:

• If the image will be used both in Mac and Windows choose MS-DOS (FAT) format for images less than 32GB, or ExFAT for images larger than 32GB
• If the macOS version is Sierra or earlier than choose Mac OS Extended
• If the macOS version is High Sierra or later, e.g. Mojave, choose APFS.

There are case-sensitive and case-insensitive options for macOS images. The safest approach is to stick to case-insensitive; they are defaults in macOS. Additionally, some applications may fail when accessing case-sensitive images.

Encryption: 128-bit is recommended, but no encryption provides a faster image.

Partition: Select Single Partition – Guid Partition Map. It is used with Intel-based MacBooks. Apple Partition Map is used with older PowerPC Macs. Master Boot Record Partition Map is used for bootable Windows images.

Image format: If you are not DVD/CD master, then you have a choice between read/write disk image and sparse images. When image format is set read/write then the new image will claim the entire size on disk as soon as it is created.

Sparse images allow creating a small initial image which will expand up to a predefined size. For instance, you can create a 100 MB file and upload only 5MB initially. The size of the image will be 5MB until you add more files. Note, however, the file will not shrink if you delete files. Once expanded it does not contract.

The difference between the sparse image and sparse bundle image is that the former consists of one giant file and bundle consist of a bunch of smaller files. When choosing between two options go with sparse bundle image (the other option is for compatibility with older Mac versions).

It is possible to change either encryption or image format after the image was created. To change encryption or image format start Disk Utility. In the menu go to Images -> Convert. Select the image, change the settings and click Convert.

The Disk Utility will create a new image, it will not override the existing one. So before converting make sure that you have enough storage for both images.

What Opens A Dmg File

Another way to create an image is from an existing folder. For instance, you may want to create a secret image to store personal files.

Installing apps with DMG files

Since DMG is a container for an app or its installer the process of installing can be one of two following scenarios:

1. When DMG file is mounted then it may ask to move the app to the Applications folder. All you need is to drag and drop the icon to the Applications folder icon.
2. If the file contains the app installer then double-clicking on the installer will start a wizard which will ask questions and eventually install the app in the Applications folder.
   Once the app is installed it is safe to delete the DMG file. In fact, it is recommended to delete unused DMG files to clean the space on Mac. First, unmount it by right-clicking and select Eject from the pop-up menu and then delete the image file.

Can’t delete DMG file?

If any file from DMG file is in use (open with another application) then macOS will not allow deleting the file. Close the application that uses the files from DMG. In case when it is not clear which application is using files from the image restarting Mac will unlock the files.

Additionally, make sure that the disk is unmounted before deleting its DMG file. Sometimes, macOS allows to delete the image file while disk is still mounted, but this is not a good practice.

Why developers use DMGs to install apps on Mac

There are multiple reasons for choosing this format to install the software. Among them are:

1. DMG files can be signed. macOS has an option to install software from the App Store only or from the App Store and identified developers. If a developer is a well-known company, e.g. Microsoft, then it gives the user additional assurances that the software came from the developer they trust.
2. DMG files cannot be tampered with. So if Microsoft has signed the Skype package it is safe to copy from another computer and install it.
3. DMG can be branded with custom icons and background images.
4. DMGs can be encrypted.

DMG on Windows

Do DMG files work on Windows?

By default, Windows does not support DMG format. If you want to create an image which can be used between Mac and Windows, then install an application such as 7-zip to open DMG files on Windows.

Note however that 7-zip will only open the image as read-only, you will not be able to add new files or change existing ones.

But make sure that selected configuration for the image file is supported with 7-zip on the Windows you are running. I was able to open an image file with Mac OS Extended and MS-DOS FAT formats, but couldn’t open the one in ExFAT.

There are other options which can extract from DMGs in multiple formats. One of the DMG extractor from reincubate. It’s a paid app, but they do have a free version. Another app is a DMG viewer from Data Forensics which works also with corrupt DMG files.

One thing to remember is that macOS and Windows are different operating systems and applications written for macOS will not work in Windows and the opposite is also true.

So, if you were hoping to install a Mac app on Windows by opening a DMG file on Windows then I have to disappoint you – this won’t work. You can exchange files that are supported on both systems, e.g. .docx or .txt, but binaries are not compatible.

DMG conversion

DMG file to ISO

ISO is another virtual disk image usually used to make a copy of a DVD/CD. It also has to be mounted just like DMG. If you need to convert DMG to ISO format you will need a third-party application.

An example of such application is dmg2iso, it’s free, but it was not maintained for a long time. Another example is AnyToISO – a paid application from Crystal Idea.

Using with VirtualBox

Oracle VirtualBox is virtualization software. The beauty of VirtualBox is that you can run the entire computer inside another computer. For instance, if you need to run Windows on Mac one option is to run a VirtualBox and install Windows OS on VirtualBox instance.

VirtualBox supports DMG formats as one of the external devices. In order to use DMG with VirtualBox add the image as a virtual optical drive. The image cannot be used a hard drive because it cannot write into it.

Using with VMware

Currently, VMware does not support the DMG format. If you want to use the image with VMware you have to convert it first to ISO.

Conclusion

DMG is not a self-extracting archive which runs and installs software on Mac. It is, however, a container which includes the software to be installed. Disk images by themselves are not dangerous, but they might carry malware inside, so be careful when downloading them over the internet.

Disk images can also be used for personal use, e.g. when you need to package personal files in one container.

Topics: