Dmg Files Not Mounting On Mac

Apple Disk Image
The icon represents an internal hard drive within a generic file icon.
Filename extension.dmg, .smi, .img
Internet media typeapplication/x-apple-diskimage
Uniform Type Identifier (UTI)
Developed byApple Inc.
Type of formatDisk image

These days, most software is downloaded over the internet. Mac OS X has popularized the use of Disk Images (.dmg files) as a means of transferring software. They're easy to use once you get how they work. The.dmg file is the actual file that contains all the data. When you double click the.dmg file, it mounts a 'virtual' disk to your desktop. Are you facing Mac OS X DMG no mountable file system error? Do you get any errors while trying to mount an image? Well, here are the solutions to try out! Nov 12, 2019 After the software stored in the DMG file is installed, the DMG file is no longer needed. Therefore, DMG files can be deleted after installing the software. While DMG files are Mac-specific and not intended for use in Windows, there are several Windows programs that can extract their contents or convert them to other formats. And that's why it is very necessary to fix DMG no mountable file system to regain access your data. By using DMG file system you can manage and mount the complete file system easily as a normal hard drive partitioning. Besides, it allows you to lock your Mac volume in order to unknown users could not view stored file and data. OS X El Capitan suddenly can't open DMG files. Ask Question. Restoring your Mac using a Time Machine backup may be. And managed to open.dmg files by going into.

Apple Disk Image is a disk image format commonly used by the macOS operating system. When opened, an Apple Disk Image is mounted as a volume within the Macintosh Finder.

An Apple Disk Image can be structured according to one of several proprietary disk image formats, including the Universal Disk Image Format (UDIF) and the New Disk Image Format (NDIF). An Apple disk image file's name usually has '.dmg' as its extension.


Apple Disk Image files are published with a MIME type of application/x-apple-diskimage.

Different file systems can be contained inside these disk images, and there is also support for creating hybrid optical media images that contain multiple file systems.[1] Some of the file systems supported include Hierarchical File System (HFS), HFS Plus, File Allocation Table (FAT), ISO9660 and Universal Disk Format (UDF).[1][2]

Apple Disk Images can be created using utilities bundled with Mac OS X, specifically Disk Copy in Mac OS X v10.2 and earlier and Disk Utility in Mac OS X v10.3 and later. These utilities can also use Apple disk image files as images for burning CDs and DVDs. Disk image files may also be managed via the command line interface using the hdiutil utility.[3]

In Mac OS X v10.2.3, Apple introduced Compressed Disk Images[4] and Internet-Enabled Disk Images for use with the Apple utility Disk Copy, which was later integrated into Disk Utility in 10.3. The Disk Copy application had the ability to display a multi-lingual software license agreement before mounting a disk image. The image will not be mounted unless the user indicates agreement with the license.[5]

An Apple Disk Image allows secure password protection as well as file compression, and hence serves both security and file distribution functions; such a disk image is most commonly used to distribute software over the Internet.

Mac Dmg File Download


Apple originally created its disk image formats because the resource fork used by Mac applications could not easily be transferred over mixed networks such as those that make up the Internet. Even as the use of resource forks declined with Mac OS X, disk images remained the standard software distribution format. Disk images allow the distributor to control the Finder's presentation of the window, which is commonly used to instruct the user to copy the application to the correct folder.

A previous version of the format, intended only for floppy disk images, is usually referred to as 'Disk Copy 4.2' format, after the version of the Disk Copy utility that was used to handle these images.[1] A similar format that supported compression of floppy disk images is called DART.[1][6]

New Disk Image Format (NDIF) was the previous default disk image format in Mac OS 9,[1] and disk images with this format generally have a .img (not to be confused with raw .img disk image files) or .smi file extension. Files with the .smi extension are actually applications that mount an embedded disk image, thus a 'Self Mounting Image', and are intended only for Mac OS 9 and earlier.[7][2]

Universal Disk Image Format (UDIF) is the native disk image format for Mac OS X. Disk images in this format typically have a .dmg extension.[1]

File format[edit]

Apple has not released any documentation on the format, but attempts to reverse engineer parts of the format have been successful. The encrypted layer was reverse engineered in an implementation called VileFault[8] (a spoonerism of FileVault).

Apple disk image files are essentially raw disk images (i.e. contain block data) with some added metadata, optionally with one or two layers applied that provide compression and encryption. In hdiutil these layers are called CUDIFEncoding and CEncryptedEncoding.[1]

UDIF supports ADC (an old proprietary compression format by Apple), zlib, bzip2 (as of Mac OS X v10.4), and LZFSE (as of Mac OS X v10.11)[9] compression internally.


The trailer can be described using the following C structure.[10] All values are big-endian (PowerPC byte ordering)

Here is an explanation:

Position(in Hex)Length (in bytes)Description
0004Magic bytes ('koly').
0044File version (current is 4)
0084The length of this header, in bytes. Should be 512.
0188Data fork offset (usually 0, beginning of file)
0208Size of data fork (usually up to the XMLOffset, below)
0288Resource fork offset, if any
0308Resource fork length, if any
0384Segment number. Usually 1, may be 0
03C4Segment count. Usually 1, may be 0
04016128-bit GUID identifier of segment
0504Data fork checksum type
0544Data fork checksum size
058128Data fork checksum
0D88Offset of XML property list in DMG, from beginning
0E08Length of XML property list
0E8120Reserved bytes
1604Master checksum type
1644Master checksum size
168128Master checksum
1E84Unknown, commonly 1
1EC8Size of DMG when expanded, in sectors
1F412Reserved bytes (zeroes)


There are few options available to extract files or mount the proprietary Apple Disk Image format. Some cross-platform conversion utilities are:

  • dmg2img was originally written in Perl; however, the Perl version is no longer maintained, and the project was rewritten in C. Currently, without additional tools, the resulting images may be mounted only under Mac OS X and under Linux (provided hfsplus support has been enabled). UDIF ADC-compressed images have been supported since version 1.5.[11]
  • DMGEXtractor is written in Java with GUI, and it supports more advanced features of dmg including AES-128 encrypted images but not UDCO images.[12]
  • 7-Zip, including the free cross-platform port of its command-line interface, p7zip.

In Windows, most dmg images can be opened using several other programs such as UltraISO and IsoBuster. MacDrive can also mount simple dmg files as drives under windows, but not sparse disk or encrypted dmgs.[13] A free Apple DMG Disk Image Viewer also exists.[14]

In Linux and possibly other Unix flavors, most .dmg files can be burned to CD/DVD using any CD-burner program (using cdrecord directly or a front-end such as K3B or Brasero) or directly mounted to a mountpoint (e.g. mount -o loop,ro -t hfsplus imagefile.dmg /mnt/mountpoint).[15][16] darling-dmg is a FUSE module enabling easy DMG file mounting on Linux.[17]

See also[edit]


  1. ^ abcdefg'hdiutil(1) Mac OS X Manual Page'. Archived from the original on 2016-05-14. Retrieved 2016-05-14.
  2. ^ ab'Mac OS X: Using Disk Copy disk image files'. Archived from the original on 2013-12-19. Retrieved 2013-04-25.
  3. ^hdiutil(1) – Darwin and macOS General Commands Manual
  4. ^'Re: Some apps refuse to launch in 10.2.8! (OT, but very important)'. Archived from the original on 2014-01-17.
  5. ^'Guides'. Apple. Archived from the original on 2009-03-06. Retrieved 2010-10-27.
  6. ^'DART 1.5.3: Version Change History'. Archived from the original on 2013-12-19. Retrieved 2013-04-25.
  7. ^'Software Downloads: Formats and Common Error Messages'. Archived from the original on 2010-12-24. Retrieved 2009-05-06.
  8. ^'VileFault'. 2006-12-29. Archived from the original on 2007-01-09. Retrieved 2010-10-27.
  9. ^Michael Tsai (2015-10-07). 'LZFSE Disk Images in El Capitan'. Archived from the original on 2017-04-09. Retrieved 2017-04-09.
  10. ^'Demystifying the DMG File Format'. Archived from the original on 2013-03-17.
  11. ^'dmg2img'. Archived from the original on 29 November 2010. Retrieved 2010-10-27.
  12. ^'DMGExtractor'. Archived from the original on 2011-01-02. Retrieved 2011-01-03.
  13. ^MacDrive Features / Boot Camp / System Requirements /. 'MacDrive Home page'. Mediafour. Archived from the original on 4 October 2010. Retrieved 2010-10-27.
  14. ^Olivia Dehaviland (2015-03-03). 'Apple DMG Disk Image Viewer'. Archived from the original on 2015-04-02. Retrieved 2015-03-10.
  15. ^'How To Convert DMG To ISO in Windows, Linux & Mac'. Archived from the original on 2010-03-07.
  16. ^'Convert DMG To ISO using PowerISO'. Archived from the original on 2009-05-02. Retrieved 2009-02-15.
  17. ^'darling-dmg'. darling-dmg. Retrieved 29 March 2015.

External links[edit]

  • Apple Developer Connection A Quick Look at PackageMaker and Installer
  • O'Reilly Mac DevCenter Tip 16-5. Create a Disk Image from a Directory in the Terminal
Retrieved from ''

DMG files are containers for apps in macOS, from which you can install software fast. Installing software simply requires you to open the .dmg file and then drag the application to your Mac’s Application folder. That’s much easier than using an Install Wizard in Windows. However, some of Mac newbies have no idea how to mount .dmg files in macOS or for some reason the .dmg file cannot be opened. Now this page will show you three methods to open and mount .dmg files on macOS.

Method 1: Open .dmg file with DiskImageMounter

DiskImageMounter is the utility that handles mounting disk images in Mac OS X. Normally you can mount a .dmg file on Mac by simply double-clicking it or right-clicking on it and selecting Open With > DiskImageMounter (default). However, some people report that .dmg files cannot be opened on Mac in this way. If that’s the case, move on to another method.

Method 2: Mount .dmg file from Mac OS Terminal

Place the .dmg file on your Mac’s desktop and then follow the steps.

Step 1: Open Terminal on your Mac. If Terminal is not on the Dock, open it from Finder > Applications > Utilities.

Step 2: Type cd ~/Desktop and press Enter key.

Step 3: Type hdiutil attach googlechrome.dmg and press Enter key. Replace googlechrome with your .dmg file name.

That’s it. After you execute the two command lines, the .dmg file will be mounted on your Mac.

Method 3: Mount .dmg file using iSumsoft Bitlocker Reader for Mac

If you cannot open .dmg files on your Mac using either of the first two methods, it’s a good idea to use a third-party utility like iSumsoft Bitlocker Reader for Mac. iSumsoft Bitlocker Reader for Mac is mainly to help unlock BitLocker-encrypted drive on Mac, but it also comes with the Attach feature that can attach disk image on Mac. Here are the simple steps you can take to mount .dmg file using iSumsoft Bitlocker Reader for Mac.

Dmg Files Not Mounting On Mac Windows 10

Dmg installer for mac

Step 1: Download and install iSumsoft Bitlocker Reader for Mac on your Mac computer. After the installation is complete, launch it from the Launchpad.

Step 2: Click the Attach button.

Step 3: Browse for the .dmg file and select it, and then click Open.

Dmg Files Not Mounting On Mac Download

That’s it. The .dmg file is now mounted successfully on your Mac and you can open it. You can also click the Unmount button to unmount the disk image from your Mac if you want.

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