I've discovered a strange problem. If I have disk image files (DMGs) which reside on a read-only NFS share, I cannot open these in Mac OS X 10.7.5. The same files open fine when accessed over AFP. However, trying to open them using hdiutil attach when they're on the NFS share results in 'attach failed - Read-only file system'.

1. 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. New Disk Image Format (NDIF) was the previous default disk image format in Mac OS 9, and disk images with this format generally have a.img (not to be confused with raw.img disk image files) or.smi file.
2. Once Free DMG Extractor is fired up, click Open and use the built-in file browser to locate and open a.dmg file. You can explore the container's contents in the main window in a tree view.

• Feb 28, 2006 In the Disk Utility app on your Mac, choose Images Convert, select the disk image file you want to convert, then click Open. Click the Image Format pop-up menu, then choose a new image format. Read-only: The disk image can’t be written to, and is quicker to create and open.
• Jun 23, 2020 How to Install and Open.dmg Files on a Mac Software installation with Mac OS X is very different than in the Windows world. On a Windows PC you run an installer, tick off a few checkboxes, and wait for the progress meter to reach completion.
• Was trying to install virtualbox on mac os x leopard. But I can't open the.dmg-file I downloaded from the sun homepage. There's a message saying 'Keine aktivierbaren Dateisysteme', something like 'no active filesystems'. Where could be the problem?
• In attempting to use Disk Utility to make a.dmg image file archive of a volume on my Mac. Can't figure out why Apple would redesign Disk Utility to not unmount.

A file extension format like DMG Apple Mac OS X Disk Image is a standard way that information is encoded for storage in a computer file. The file extension DMG Apple Mac OS X Disk Image format specifies how bits are used to encode information in a digital storage medium. File formats may be either proprietary or free and may be either unpublished or open. Jan 06, 2016 Currently, the only way to open a.dmg disk image in Mac OS 9 is to use either the developer version of Disk Copy (version 6.4), or a beta version of the unreleased 6.5. However, both versions can only open uncompressed images; compressed Disk Images are unusable on Mac OS 9. The files replaced IMG files when Mac OS X was released. Extract any file from a DMG archive with just a few clicks! Open macOS DMG files on Windows. Extract any file from a DMG archive with just a few clicks! DMG EXtractor will open and extract Mac OS X dmg files on PC. Watch how it's done (1:04) Our users are saying 'I extracted a very important.dmg file! DMG Extractor worth every penny.'

One of the major differences between Windows and macOS is the way they read, write, and install files and applications. For example, Windows uses .exe files to execute programs while macOS uses a .pkg file to install an app or a .dmg file to clone existing drives. Some app installers also come in DMG format and the Mac user just needs to mount the file to extract the installer and run the package.

But for some reason, several Mac users have been experiencing issues with DMG files. For example, one user posted on Apple’s support website about his Mac not being able to recognize the DMG files he created as a backup. The user had to do a clean install of the entire operating system, so he saved the important data in a DMG format. Unfortunately, once his Mac was back up and running again, the DMG files he created were not recognized by the freshly installed operating system.

Other Mac users encountered the error when downloading files from the internet, such as app installers or software updates. The files seemed to be downloaded successfully, but when they try to mount the DMG file, they get a notification that the disk image can’t be opened because macOS can’t recognize the file. There are also instances when macOS says that the DMG file can’t be mounted because it is still being downloaded, but the file has been downloaded completely on the device.

This error can be quite irritating if you want to install a specific app on your Mac and the downloaded installer from the internet is not recognized by macOS. What’s even more frustrating is when the DMG files you want to mount are your backup files from your previous macOS installation and they contain important data and files.

If you are getting this error when opening your DMG files, this guide will be quite helpful for you to resolve this error and successfully run your problematic DMG files.

What is a DMG File?

Before discussing the error, let us first understand what a DMG file is and what it is used for. DMG is a file format that you usually encounter when using a Mac. A DMG file, also known as Apple Disk Image or macOS Disk Image file, is a digital reconstruction of your physical hard drive. It is the macOS version of Windows’ ISO files. If you’ve worked with Windows before, then you have a pretty good understanding of what an ISO file is. A DMG file works the same way as ISO files.

Just like ISO files, the DMG file format is often used to save compressed app installers instead of using physical disks. You’ll notice that most macOS software that is downloaded from the internet is in this format. The Apple Disk Image supports file compression, file spanning, and encryption. So don’t be afraid when you are asked for a password when you try to run a DMG file.

Free Dmg File Downloads

DMG files are available only for Macs that run OS X 9 and later versions. For those with older Macs, the IMG file format is used instead.

DMG files were created for macOS, so opening or running it on a Mac should be very simple. When you copy the DMG file or you connect the drive where the DMG file is saved, it is automatically mounted by macOS as a drive and is treated as an actual hard drive.

DMG File Not Recognized Error on Mac

Launching a DMG file should be a straightforward process, but that’s not the case for everyone. For some reason, some Mac users are getting the “DMG file not recognized” notification whenever they try to mount their files. An error window that lists down the problematic files pops up, along with the following error message:

The following disk images couldn’t be opened.

Reason: not recognized.

Because of this, users are not able to access their files or install the software in the DMG file. This error can be caused by several different factors, so users need to investigate closely to find out what went wrong.

One possible reason why macOS can’t recognize your DMG file is because it is corrupted. If you downloaded the file from the internet, it could be that the file itself is corrupted or something happened when you were downloading the file.

If you created the file as a backup from your existing files, it is possible that something went wrong during the conversion process. An outdated operating system can also cause your file system to not function properly, leading to errors such as this.

So what do you do when you get this error?

How to Fix the ‘DMG File Not Recognized’ Error

It can be frustrating when you get this error, especially if the DMG file contains your backup files and you can’t seem to retrieve them. When you get the “DMG file not recognized” error on Mac, you need to consider various factors to determine the cause of the problem. From there, you can easily fix the problem by referring to our guide below.

Step 1: Check Your Internet Connection.

When you download the DMG files from the internet, make sure that your internet connection is stable and strong. Switch to wired connection if possible. An incompletely downloaded DMG file will not run because of the missing components.When your download gets interrupted because of power interruption or poor internet connection, the file is not successfully downloaded, causing errors at the end.

Step 2: Download From Official Sources Only.

If you’re downloading an app, get the installer from official websites only or the Mac App Store. When you download from somewhere, you have no idea whether the app is fake or is bundled with malware. To make sure you’re downloading a clean and complete DMG file, get it from official sources only.

Can't Open Dmg File Mac

Step 3: Clear Out the Junk Files.

When you have too many unnecessary files on your Mac, the system gets cluttered and file system errors appear. Clean up your files and optimize your Mac using Outbyte MacRepair. Make it a habit to perform regular maintenance tasks to avoid future errors.

Step 4: Try to Open the File on Another Mac.

It is possible that the error has something to do with your Mac, so you might need to try it on a different Mac to rule this factor out. If the DMG file is successfully mounted on a different computer, then you can be sure that there is no problem with your file. What you need to figure out next is why your computer can’t recognize it.

The converse is also true: if the file doesn’t open on another Mac, then the file itself is the problem. If this is the case, redownload the file from another source and see if this makes any difference.

Step 5: Mount the DMG File Using DiskImageMounter.

Can't Open Dmg File Mac Sierra

The DiskImageMounter is the default app designed to automatically open DMG files. If you’re having problems mounting the DMG file, you can do it manually using the instructions below:

1. Right-click on the file, then choose Get Info.
2. In the Get Info window, scroll down to the Open with: section.
3. Click on Open with: and choose DiskImageMounter from the pop-up menu.
4. If you don’t see DiskImageMounter listed among the options in the pop-up menu, select Other instead.
5. When the Finder window appears, go to /System/Library/CoreServices/.
6. Locate the DiskImageMounter and click on it.
7. Click on the Change All button.
8. Click the Continue button when you see the confirmation message.

Open Dmg File With Windows

You should now be able to mount your DMG file using DiskImageMounter.

Step 6: Open the File Using Disk Utility.

When you can’t open the DMG file using ordinary means, another option is to use Disk Utility to open it and save the contents using a different format. To do this, follow the steps below:

1. Open Disk Utility by going to Finder > Go > Utilities.
2. Click on the DMG file you want to open from the list of drives on the left.
3. Click on 7-Zip or DMG Extractor to at the upper left portion of the window.
4. Rename the file to differentiate the old from the new version. For example, sample becomes samplenew.
5. Click on Save and wait for the file to be converted.

Unable To Open Dmg File On Mac

Once the process has been completed, you will now be able to open the contents of the DMG file.

Step 7: Extract the Content of the DMG File Using a Third-Party App.

If you can’t mount the DMG file on your Mac in the first place, you can’t use Disk Utility to open it. Your last option would be to use a third-party extractor to get access to the files. You can use 7-Zip or DMG Extractor to open the DMG file. Just install the app, right-click on the DMG file you’re having trouble with, extract the files and save them to a folder you can easily access.

Dmg2img

Summary

How To Open .dmg File

DMG files are great for installing apps on Mac and for creating backup images of your files. Its encryption and compression functions also make it a lot more secure compared to other file formats. However, it can also be troublesome when macOS fails to recognize the file because you can’t open it or access the contents. If this happens to you, don’t worry because you have several options. You can try any or all of the steps above to successfully mount your DMG file.

Cannot Open Dmg File On Mac

When you download an app or a piece of software on your Mac, the file is usually downloaded as a DMG file. DMG files serve as containers for apps in macOS. You just need to double-click the downloaded DMG file, drag the app to the Applications folder, then unmount the installer. This way, the installation process has been simplified and users don’t have to suffer the hassle of installation wizards that are plaguing Windows users.

Although the installation process sounds simple, it is much more complicated than that. The contents of the DMG goes through a checksum process to verify that the file is 100% intact and that it hasn’t been tampered with. Once the file has been verified, it is then decompressed. DMG files are designed for macOS and you can’t run them on Windows devices.

DMG files make app installations on macOS a lot quicker and easier. However, there have been several reports from users about the .dmg file not opening on Mac. There are different versions to this error, but the end scenario is the same: for some reason, users are unable to open the .dmg file on Mac. This guide will discuss why some users have trouble opening a DMG file and how to resolve this issue.

Unable to Open .DMG File on Mac

Installing a DMG file on Mac should be as easy as double-clicking the file and dragging the app to the Applications folder. However, the process is not as smooth for some Mac users because they are not able to open the DMG file to start with. According to user reports, the download process was completed and there were no issues with unzipping. But when it comes to opening the unzipped files, nothing happens. Some users who encounter this issue get the resource temporarily unavailable error while others noted no activity happening no matter how many times the file is clicked.

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Others encounter this error message when opening the DMG file:

There is no default application specified to open the document.

When the user tries to open it, either the options are grayed out or nothing happens when any of the options are clicked. This error has caused the affected Mac users to be frustrated. The users who encountered this error tried to redownload the file using a different Mac and the DMG file seems to be working fine, which means that the problem lies with the device itself. But what causes DMG files to not open on Mac?

Why Your .DMG File Is Not Opening on Mac

Some users noted that they cannot open the .dmg file on Mac after updating to Catalina, but there are also those who encountered this error when running an older version of macOS. This means that the problem is not unique to Catalina but it is something that affects the entire macOS system.

Here are some of the possible reasons why some users are having trouble opening DMG files:

• If your Mac is running Catalina, check the version of the app you are trying to open. Catalina no longer supports 32-bit apps. So if you’re trying to download and install a 32-bit app, then you might not be able to install it on Catalina.
• If you have poor or unstable internet connection, it is possible that the file was not downloaded completely, resulting in errors when accessing the file.
• If you downloaded the file from an untrustworthy source, it might be a fake DMG file or it could be loaded with malware.
• It is also likely that the DMG file you downloaded is corrupted. An interrupted download process and malware infection are the two leading causes of file corruption.

Hence, before you start the troubleshooting process, here are some things you need to consider:

• Download the file once again using a different internet connection. Try using a wired connection if possible.
• Scan the file for malware infection, especially if the file was downloaded from an untrustworthy source.
• Download the file from another source. If the app is not available on the Mac App Store, visit the developer’s website and download the installer from there instead.
• If you’re running macOS Catalina, make sure that you are downloading the 64-bit version of the app.

How to Open .DMG File on Mac

If you’re having trouble opening the DMG file on Mac, here are some of the things you can do:

Method #1. Use DiskImageMounter.

1. After downloading the DMG file, right-click or Command + click on the file.
2. Choose Open With from the menu, then select DiskImageMounter.
3. Depending on the size of your file, you should see the mounted Disk Image appear on your Desktop.
4. If you don’t see the Disk Image, choose Other from the right-click menu.
5. Navigate to /System/Library/CoreServices/DiskImageMounter.app
6. The DMG file should now be mounted.

Method #2. Mount the .DMG File via Terminal

If the right-click menu is grayed out or nothing happens when you click any of the Open With options, you can try mounting the file using Terminal instead. Drag the file to the Desktop and follow the steps below:

1. Open the Terminal app by going to Finder > Applications > Utilities.
2. In the Terminal window, type in the following command and press Enter: cd ~/Desktop
3. Next, type in this command, then press Enter: hdiutil attach filename.dmg
4. Replace filename.dmg with the actual .dmg file name.
5. After executing the two command lines, your .dmg file will now be mounted on your Mac.

Method #3: Use a Third-Party Tool.

If you cannot open the DMG file using the two methods above, you can try using a third-party utility instead. Here are some of the apps you can try:

Summary

Installing applications on macOS is a lot simpler compared to installing programs on Windows, thanks to the DMG file. However, it is normal to run into errors when opening a DMG file, especially if the file has been corrupted or has not been completely downloaded on your device. If this is the case, you can try any of the three methods listed above to open the problematic DMG file.