Manipulate disk images (attach, verify, burn, etc).

Disk images are containers that emulate disks. Like disks, they can be partitioned and formatted. Many uses of disk images blur the distinction between the disk image container and its content, but this distinction is critical to understanding disk images. The terms 'attach' and 'detach' are used to distinguish the way disk images are connected to and disconnected from the system.
For example, when you double-click a disk image in the macOS Finder, two separate things happen. First, the image is 'attached' to the system just like an external drive. Then, the kernel and Disk Arbitration probe the new device for recognized file structures. If any file structures are understood, the associated volumes will mount and appear in the
Finder.
Always consider whether a 'disk image' operation applies to the blocks of the disk image device or to the (often file-oriented) content of the image. For example, verify verifies that the blocks stored in a read- only disk image have not changed since it was created. On the other hand, create -srcfolder creates a disk image container, puts a filesystem
in it, and then copies the specified files to the new filesystem.

Fixes an issue that prevented some users from deleting custom snap areas which had keyboard shortcuts assigned. Vmware tools dmg.

As of macOS 10.5, a more reliable, efficient, and scalable sparse format, UDSB (SPARSEBUNDLE), is recommended for persistent sparse images as long as a backing bundle (directory) is acceptable. macOS 10.5 also introduced
F_FULLFSYNC over AFP (on client and server), allowing proper journal flushes for HFS+J-bearing images. Critical data should never be stored in sparse disk images on file servers that don't support F_FULLFSYNC.
SPARSE (UDSP) images and shadow files were designed for intermediate use when creating other images (e.g. UDZO) when final image sizes are unknown. As of macOS 10.3.2, partially-updated SPARSE images are properly handled and are thus safe for persistent storage. SPARSE images are not recommended for persistent storage on versions of macOS earlier than 10.3.2 and should be avoided in favor of SPARSEBUNDLE images or UDRW
images and resize.
If more space is needed than is referenced by the hosted filesystem, hdiutil resize or diskutil(8) resize can help to grow or shrink the filesystem in an image. compact reclaims unused space in sparse images. Though they request that hosted HFS+ filesystems use a special 'front first' allocation policy, beware that sparse images can enhance the
effects of any fragmentation in the hosted filesystem.
To prevent errors when a filesystem inside of a sparse image has more free space than the volume holding the sparse image, HFS volumes inside sparse images will report an amount of free space slightly less than the amount of free space on the volume on which image resides. The image filesystem currently only behaves this way as a result of a direct attach action and will not behave this way if, for example, the filesystem is unmounted and remounted.

Nov 11, 2019  It would be nice if you could resize volumes without having to delete a volume and lose any information you have stored there. With the new Disk Utility, that isn't directly possible, but under the right circumstances, you can resize without losing data, although in a somewhat complicated manner.

/dev Entry Access

Since any /dev entry can be treated as a raw disk image, it is worth noting which devices can be accessed when and how. /dev/rdisk nodes are character-special devices, but are 'raw' in the BSD sense and force block-aligned I/O. They are closer to the physical disk than the buffer cache. /dev/disk nodes, on the other hand, are buffered block-special
devices and are used primarily by the kernel's filesystem code.
It is not possible to read from a /dev/disk node while a filesystem is mounted from it, but anyone with read access to the appropriate /dev/rdisk node can use hdiutil verbs such as fsid or pmap with it. The DiskImages framework will attempt to use authopen(1) to open any device which it can't open (due to EACCES) for reading with open(2). This might cause apparent hangs while trying to access /dev entries while logged in remotely (an authorization panel is waiting on console).
Generally, the /dev/disk node is preferred for imaging devices (e.g. convert or create -srcdevice operations), while /dev/rdisk is usable for the quick pmap or fsid. In particular, converting the blocks of a mounted journaled filesystem to a read-only image will prevent the volume in the image from mounting (the journal will be permanently dirty).

Compatibility

macOS 10.0 supported the disk images of Disk Copy 6 on Mac OS 9. macOS 10.1 added sparse, encrypted, and zlib-compressed images. These images will not be recognized on macOS 10.0 (or will attach read/write, possibly allowing for their destruction). As the sparse, shadow, and encrypted formats have evolved, switches have been added to facilitate the creation of images that are compatible with older OS versions (at the expense of the performance and reliability improvements offered by the format enhancements). In particular, sparse images should not be expected to attach on versions of macOS older than that which created them.
With macOS 10.2, the most common image formats went 'in-kernel' (i.e. the DiskImages kernel extension served them without a helper process), image meta-data began being stored both as XML and in the embedded resource fork, and the default Disk Copy.app 'compressed' format became UDZO (breaking compatibility with 10.0). macOS 10.4 introduced bzip2 compression in the UDBZ format which provides smaller images (especially when combined with makehybrid) at the expense of backwards compatibility.
In macOS 10.4.7, the resource forks previously embedded in UDIF images were abandoned entirely to avoid metadata length limitations imposed by resource fork structures. As a result, UDIF images created on 10.4.7 and later will not, by default, be recognized by either macOS 10.1 or macOS 10.0. flatten can be used to customize the type of metadata stored in the image.
macOS 10.5 introduced sparse bundle images which compact quickly but are not recognized by previous OS versions. macOS 10.6 removed support for attaching SPARSEBUNDLE images from network file servers that don't support F_FULLFSYNC.
macOS 10.7 removed double-click support for images using legacy metadata; these can be rehabilitated using flatten and unflatten, or convert.

History

Disk images were first invented to electronically store and transmit representations of floppy disks for manufacturing replication. These images of floppies are typically referred to as 'Disk Copy 4.2' images, in reference to the application that created and restored them to floppy disks. Disk Copy 4.2 images were block-for-block representations of a floppy
disk, with no notion of compression. DART is a variant of the Disk Copy 4.2 format that supported compression.
NDIF (New Disk Image Format) images were developed to replace the Disk Copy 4.2 and DART image formats and to support images larger than a floppy disk. With NDIF and Disk Copy version 6, images could be'attached' as mass storage devices under Mac OS 9. Apple Data Compression (ADC) -- which carefully optimizes for fast decompression -- was
used to compress images that were typically created once and restored many times during manufacturing.
UDIF (Universal Disk Image Format) device images picked up where NDIF left off, allowing images to represent entire block devices and all the data therein: DDM, partition map, disk-based drivers, etc. For example, it can represent bootable CDs which can then be replicated from an image.
To ensure single-fork files (NDIF was dual-fork), it began embedding its resource fork in the data fork. UDIF is the native image format for OS X.
Raw disk images from other operating systems (e.g. .iso files) will be recognized as disk images and can be attached and mounted if macOS recognizes the filesystems. They can also be burned with hdiutil burn.

What's New

In macOS 10.12 Apple will provide an updated hdutil command able to work with the new file system.

macOS 10.7 added the ability to quickly render encrypted images inaccessible using the new erasekeys verb, which saves time versus securely overwriting the entire image.
In macOS 10.6, pmap was rewritten to use MediaKit's latest reporting routines so that it can properly support GPT partition maps. Also -debug now implies -verbose for all verbs.
macOS 10.5 changed the behavior of attach when run on an existing image or /dev node: if the image was attached but no volume was mounted, the volume would be mounted. Prior systems would return the /dev without mounting the volume. This change effectively removes the ability to create a second /dev node from an existing one.

Examples

Mount a Disk Image:
$ hdiutil attach /path/to/diskimage.dmg

Unmount a Disk Image:
$ hdiutil detach /dev/disk2s1

Create a Disk Image from a folders contents:
$ hdiutil create -volname 'Volume Name' -srcfolder /path/to/folder -ov diskimage.dmg 5e dmg must read sections book.

Create an encrypted Disk Image from a folders contents:
$ hdiutil create -encryption -stdinpass -volname 'Volume Name' -srcfolder /path/to/folder -ov encrypted.dmg

The required password can be piped into the hdiutil command:
echo -n SEcurePa$$w0rd | hdiutil..

Burn a Disk Image file (.iso, .img or .dmg) to a DVD:
$ hdiutil burn /path/to/image_file

“The beginning of wisdom is to call things by their right names” - Chinese Proverb

Related macOS commands:

asr - Apple Software Restore.
dd - Convert and copy a file, clone disks.
diskutil - Disk utilities - Format, Verify, Repair.
ditto - Copy files and folders.
authopen(1), hdid(8), ioreg(8), drutil(1), msdos.util(8), hfs.util(8), diskarbitrationd(8), /System/Library/CoreServices/DiskImageMounter.app.

For example:$ java -versionjava version ' 13'Java(TM) SE Runtime Environment (build 13)Java HotSpot(TM) 64-Bit Server VM (build 23.2-b04, mixed mode)To run a different version of Java, either specify the full path, or use the javahome tool. For example:$ /usr/libexec/javahome -v 13 -exec javac -version. Download mac os x dmg. If the installed version is 13 Interim 0, Update 0, and Patch 0, then you see a string that includes the text 13. After installing Java for macOS 2012-006, can I continue to use Apple's Java 6 alongside the macOS JDK for Java 13?If you want to continue to develop with Java 6 using command-line, then you can modify the startup script for your favorite command environment.

In computing world, DMG or (Disk Image File) is a file extension that belongs to Mac OS X. DMG file can also be termed as Apple Disk Image. The icon used equivalent to this file is an Internal Hard-drive. Disk Images are generally used worldwide in-order to distribute applications and software across the Internet. DMG file provides some attractive features that allow securing password along with file compression.
These virtual or physical Apple disks can be cloned from one to another. This is one of the powerful features of Mac.

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Tip: If you want to open and view DMG files of Apple Mac OS X so, you can try DMG Viewer tool.

Why DMG Files Are Created?

Earlier, Mac applications made use of Resource fork. These are the part of file system on Mac Operating System, which consists of both the structured data and non-structured data. Mac could not transfer these Resource forks over the mixed networks. Hence, the usage of Resource fork dwindled and this was the reason that Apple created disk image formats(DMG). The Resource forks are very important as they contain Meta data regarding the file.

Mounting and Dismounting on Mac OS

It is equivalent to plugging in a removable drive, where E drive is automatically created and while removing one chooses ‘Safely Remove Device’. Similarly, you have to eject the Mac drive for both the virtual and physical.
Two Disk Formats supported are:

• NDIF
  This was previously used as the default format of Mac, also known as New Disk Format. These files generally have an .img file extension.
• UDIF
  The native disk format of Apple Mac DMG file is UDIF (Universal Disk Image Format) with a file extension of .dmg.

MIME Type of DMG File:
application/x-apple-diskimage.

Supported File Systems

• Hierarchical File System (HFS) – This was developed by Apple Inc. for the systems supporting Mac OS. Earlier, these file systems were used in floppy disks and hard disks but later were used to read CD-ROM as well. It is known as Mac OS Standard.
• HFS Plus – It was developed after HFS, which is an extension of the same. It is known as Mac OS Extended.
• File Allocation Table (FAT) – It is a file system generally compatible with all file systems and helps in exchange of data between systems.
• ISO9960 – This is also a file system which was issued by ISO (International Organization for Standard) supporting various OS and helps in exchange of data.
• Universal Disk Format –This is a file system usually used to store broadcast media like DVD and optical disk formats.

How to Open DMG Files?

In Mac:

• When you download a Disk image, all the applications in it must be copied to the Application files, because many of these files will be in read-only format. Running these files inside the drives may produce some erroneous results.
• Double clicking the DMG File will open the file and you can view the contents in it. It might be images, documents, programs, etc.
• The DMG File consists of an application file. You can simply drag and drop to install them. If there is a possibility of having an installer, you can run these files instead of installing.
• Right-click on the File >> “Eject” (click on virtual disk instead of, original file)
  Delete the old DMG Files after installing. The reason is old files may take more space when we install new programs.

Resize DMG Files

• Right click DMG File >> Click Get Info (View the original size).
• Open Disk Utility >>Select Images Tab>Click on Resize>>Select the DMG file to be resized.
• Click on Open >>Type the file size to be reduced>>Select Resize>>Done

In Windows:
Originally, DMG files are the default Disk Image file for Mac. Hence, they can be opened only on Mac OS.
Since there are no manual methods available to view the DMG Files in Windows, users can install external third-party software available online on Internet. DMG Viewer is one of the tools from such category.
The software provides you with the following features:

Resize Dmg File Remove Empty Space Video

• Open DMG File in Windows OS based machine
• Read: Corrupt, Password Protected & Encrypted DMG
• Recover permanently deleted files from DMG
• Search a specific file type in large DMG Format Files

Conclusion

Resize Dmg File Remove Empty Spaces

Considering the ongoing necessity to view DMG files, we have described a manual process to let the users understand how to open & view DMG files. Else, users can take the help of a reliable third-party tool named as DMG Viewer. It is the best application that helps to read .dmg files in Windows OS. Users can use any approach as per their choice.