You can create a disk image that includes the data and free space on a physical disk or connected device, such as a USB device. For example, if a USB device or volume is 80 GB with 10 GB of data, the disk image will be 80 GB in size and include data and free space. You can then restore that disk image to another volume.
Just downloaded and installed Monterey. A short while later I download a free trial of Logic Pro after the Monterey upgrade and clicking on the downloaded DMG file does not open the disk image mounter. The DMG icon 'blinks' like it's going to open but nothing happens. I've tried restarting the computer, didn't change anything. I tried clicking while holding 'control' to use the 'open with > DiskImageMounter' and nothing happened.
A disk image on Mac is a file format that mimics a physical disk. Like physical disks, it can be mounted in Finder, where it looks like any other volume, have files and folders copied to and from it, and can be cloned or burned onto physical media like a CD or DVD. Disk images are ejected in the same way as physical disks and show up in Disk Utility. You can also use Disk Utility to create disk images of your own.
The error was as the screenshot above shows; trying to open a dmg (disk image), macOS showed the error "no mountable file systems". If you see the "no mountable file systems error" while opening a dmg, here's what you should try:
macOS Sierra (10.12) and earlier is not able to mount the new Apple File System (APFS). So if you're on macOS Sierra (10.12) or earlier and you ran hdiutil and see references to Apple_APFS or error 112, the issue is likely legitimate incompatibility, and this disk image won't open on this Mac without an update to the operating system.
Another suggestion added by a reader (thank you, Markus!) is that filesystem errors on your main Mac drive could be the cause of the disk image mounting errors. Here are instructions from Apple for scanning and repairing errors using Disk Utility. Note that in order to scan and repair errors on your main Macintosh HD drive, you'll need to reboot your Mac into recovery mode. You'll want to choose Disk Utility in the utilities listed in the recovery mode menu.
An Apple Disk Image can be structured according to one of several proprietary disk image formats, including the Universal Disk Image Format (UDIF) from Mac OS X and the New Disk Image Format (NDIF) from Mac OS 9. An Apple disk image file's name usually has ".dmg" as its extension. A disk image is a compressed copy of the contents of a disk or folder. Disk images have .dmg at the end of their names. To see the contents of a disk image, you must first open the disk image so it appears on the desktop or in a Finder window.
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. Some of the file systems supported include Hierarchical File System (HFS), HFS Plus (HFS+), File Allocation Table (FAT), ISO9660, and Universal Disk Format (UDF).
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.
In Mac OS X v10.2.3, Apple introduced Compressed Disk Images 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 multilingual software license agreement before mounting a disk image. The image will not be mounted unless the user indicates agreement with the license.
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.
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. A similar format that supported compression of floppy disk images is called DART.
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 extension. Files with the .smi extension are actually applications that mount an embedded disk image, thus a "Self Mounting Image", intended only for Mac OS 9 and earlier.
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.
Most dmg files are unencrypted. Because the dmg metadata is found in the end, a program not understanding dmg files can nevertheless read it as if it was a normal disk image, as long as there is support for the file system inside. Tools with this sort of capacity include:
One of the problems retro Mac enthousiasts face nowadays is figuring out how to mount old/random disk images in order to access the game or app in it. First of all, you have to know that there were at least a dozen disk image formats back then (altough only a handful of them were widely used) and fortunately for you, there is a very nice disk image mounting tool for classic Mac called Virtual DVD-ROM/CD Utility that mounts just about all of them (tough, NOT ALL of them).
Around the mid 90's, Toast came into play with CD imaging. So if your image is big (e.g. 100MB or more) or ends with .iso, .cdr or if it did not come stuffed (.sit) or encoded (.hqx) then it most probably will mount using Toast. As a matter of fact, if you're unsure and your disk image is bigger than 800KB, Toast will 99% of the time successfully mount it. Try this software if you're stuck with a blank icon that doesn't open with any other application. First, install Toast 5 Titanium if you have Mac OS 8.6 to Mac OS 9.2.2. For Mac OS 8.5 and below (down to Mac OS 7.5.1), install Toast 4.
DiskCopy, bundled with late classic Mac OS versions, opens Apple's own distribution disk images such as file names that end with ".img". It's worth noting that just because you could once mount a .img file with DiskCopy does not mean that you can mount all of them with it nor with the same version of DiskCopy. Two very important notes about DiskCopy: First, altough DiskCopy will successfully mount 400KB (MFS formated) single sided floppy disk images under Mac OS 7 and older, it will NOT mount them under Mac OS 8.1 to 9.2.2, so if you've got a very old 400KB disk image, the only option is to mount it under Mac OS 7 or older. Second, disk image files created with DiskCopy *CANNOT* be copied/transfered to a non-Macintosh partition. They will get damaged and lose their resource fork, rendering them useless. So, do not unzip or expand DiskCopy images on Windows or Linux. Expand them under Mac OS to be safe. With all of that said, the rule of thumb is: DiskCopy is good to mount small (e.g. floppy or zip) disk images (often ending with .dsk or .img) that you found stuffed (.sit) or encoded (.hqx) on the internet and it's good also for all Apple disk images such as software updates and installers. DiskCopy is also responsible for file names ending with ".smi" (self mounting image) altough they're actually a standalone application and so, they will auto-mount their contents by themselves.
Tough, if you run across a .img file that DiskCopy does not recognize, then it's probably a ShrinkWrap or DiskDup disk image. ShrinkWrap was Aladdin's (the author of Stuffit) proprietary format that DiskCopy could not mount, so make sure you keep a copy of ShrinkWrap handy to mount some of the 90's floppy disk images.
DiskCopy and ShrinkWrap were pretty much the standard in disk imaging from mid 80's to mid 90's, except for some fancy users who made disk images using DiskDoubler so if you have a 90's disk image about the size of a floppy or less and it doesn't mount with aforementioned tools, then try DiskDoubler.
3) It's very well possible that Toast does not recognize the file type, in which case it will show a warning message like the following. It's totally fine and 99% of the time it will mount the disk image perfectly fine, so make sure you click "Continue" on this warning. Next, if you saw the warning message, it will then ask you to define the pregap and postgap. Don't touch any of those numbers and simply click "OK".
4) Then click the "Mount" button on the Toast window and your disk image will mount on the desktop next to your main hard disk volume. If it does not, then Toast will output an error message like this. When you see this, it almost always means this is a ShrinkWrap image or a DiskCopy image. Try ShrinkWrap as it does both.
5) Launch ShrinkWrap and pull the top menu named "Image" and choose "Mount Image..." then select your disk image file. If a window very briefly appears and disappears but then nothing else happens, it means that ShrinkWrap cannot mount this disk image. Your only hope is then DiskCopy.
It's because the sparseness is handled at a different level of abstraction for a sparse image vs. a sparse file. If you're storing a file "directly" on disk, the filesystem (e.g. HFS+) handles mapping the sequence of bytes that make up the file into a sequence of bytes on disk. A sparse file is one that has gaps in its sequence of bytes, and a filesystem that supports this will skip those missing bytes when it maps the file to disk. 2b1af7f3a8