Your Mac has a native application called Disk Utility to create a or partition. A disk image is a file that emulates a drive or volume whose image it contains. Also, the disk image file stores other files & folders just like a virtual drive and can be mounted as a volume within Finder. Generally, the native disk image format of macOS has the .dmg file extension.
The booter mounts this volume (it attaches as /dev/disk1), and transfers to OS X running on it. This is the Mac OS X Base System. Notice that the Recovery HD is only 650MB, but Mac OS X Base System is 1.4GB? That's because it's a compressed disk image (and I'm pretty sure that compression is the reason they bother with all this disk image. 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. How to Open Disk Image (DMG) Files That Are Not Allowed on a Mac. If you've got a disk image file (.dmg) that you want to open but can't because you're not an admin, this workaround can help. Download the file.
In this blog, we’ll share the Disk Utility method to create a disk image file of your Mac startup disk. We’ll also share how to restore your startup disk by using the already created image file.
The Apple Disk Image format is a MacOS, OS X, and Apple II disk image format family (which may be stored in DSK (Apple II) or nibblized disk image format) preceded by a prefix giving format information, and often a trailer with comments and other metadata. Give the disk image a name and select a destination, if you don’t have the local storage capacity for such a large disk image be sure to choose an external or network drive as the image destination Pull down the “Image Format” menu and choose “Read-only disk image”, this saves the image as the familiar DMG format.
The need for Creating Disk Image of Mac Startup Disk
You can create a disk image of your Mac startup disk:
·To burn the startup disk’s data to CDs or DVDs
·To back up your startup disk’s apps and settings
·To restore your Mac from the recovery image file
·To compress the startup disk’s data for archival purpose
·To protect startup disk’s files and folders through encryption
·To transfer startup disk’s files and folders between Macs
·To store the startup disk’s data in NAS or a different volume
Apple Disk Image Media
Prerequisite
To create a disk image of your Mac startup drive, you need any one of the following save locations with sufficient space:
·Additional volume on your Mac
·Mounted external storage drive
·Connected network storage drive
Methods to Create Disk Image of Startup Disk
First Method
First off, quit or stop any apps and services to minimize writing on to the startup drive during the image creation process. Subsequently, perform the following steps to create a disk image of your Mac startup disk:
1.Go to Applications > Utilities > Disk Utility.
2.On the Menu bar, select File > New Image > Image from Folder.
3.On the dialog window, select your startup disk (Macintosh HD) then click Open.
4.Provide a name for the disk image, add tags if needed, and specify a save location.
5.If you wish to encrypt the disk image, then click the Encryption pop-up menu and choose an encryption option.
6.Click the Image Format pop-up menu, then specify an image format. You can choose from Read-only, Compressed, Read/write, DVD/CD master, Hybrid image (HFS+/ISO/UDF)
7.Click Save then Done.
Second Method
Apple Disk Image Mounter
Boot your Mac from a different startup drive, say macOS Recovery to create a disk image of your Mac startup disk. Steps are as follows:
1.Start or restart your Mac then immediately press and hold Command + R keys together.
2.Release the keys once you see the Apple logo. Mac starts in macOS Recovery mode.
3.From the macOS Utilities window, select Disk Utility then click Continue.
4.After Disk Utility opens, perform the steps listed in the first method.
Third Method
You can create and manage your disk image file through terminal commands. Steps to create a disk image file of your Mac startup disk by using Terminal are as described below:
1.Open Terminal.
2.Type hdiutil create –volname N –srcfolder P –ov N.dmgthen press Return.
Note: Here replace N with the name of the disk image file and P with the path of the source volume.
3.Quit Terminal.
Steps to Restore a Startup Disk Image
You can restore your startup disk image file to your startup disk. But, first off, save any important files and folders present on your startup disk to another volume or storage drive to avoid data loss that will ensue due to disk erasure.
Steps to restore startup disk image file to startup disk are as follows:
1.Open Disk Utility on your Mac from macOS Recovery mode.
2.From the sidebar, select the startup disk (Macintosh HD) then click the Restore button. Note: Your startup disk will be erased and will become the replica of the image file.
3.Click the Image button then navigate to the startup disk image file.
4.Click Open then click Restore.
Conclusion
We hope this blog helped you to understand the nitty-gritty of how you can create a disk image of your Mac startup disk on your macOS Mojave. The best and safest method is to use Disk Utility—a GUI app that simplifies the image file creation process. Advanced users may try the Terminal method to create a startup disk image and manage it from there. The blog also shared the technique on how to restore a startup disk image to a startup disk by using Disk Utility.
It is a must that you back up your Mac before performing any critical troubleshooting process; for instance, when you restore from the image file to the startup drive. The wrong choice of the source and the destination drive could result in data loss. In such a dire situation, a Mac data recovery software can be your savior. The software can salvage your precious data that got lost due to accidental erasure or other logical data loss scenarios.
Apple Disk Images
Developer(s) | Apple Computer |
---|---|
Stable release | |
Operating system | Mac OS X |
Type | Disk image emulator |
Website | www.apple.com |
DiskImageMounter is the utility that handles mounting disk volume images in Mac OS X, starting with version 10.3. DiskImageMounter works by either launching a daemon to handle the disk image or by contacting a running dæmon and have it mount the disk.
Like BOMArchiveHelper, DiskImageMounter has no GUI when double-clicked; doing so does nothing. The only GUI the program ever displays is a window with a progress bar and mount options (cancel or skip verification) or an error report if it could not mount the image. It is found in /System/Library/CoreServices/DiskImageMounter.app.
Starting with version 10.7, Apple 'removed double-click support for images using legacy metadata.'[1] DiskImageMounter will not be able to open .img (NDIF only), .smi (self mounting), .dc42 (Disk Copy 4.2), and .dart (DART) disk image formats that was previously supported in version 10.6 and earlier.
Image formats supported[edit]
DiskImageMounter supports a variety of disk image file types:[2]
- Apple Disk Image (.dmg, com.apple.disk-image)
- UDIF disk images (.udif, com.apple.disk-image-udif); UDIF segment (.devs, .dmgpart, com.apple.disk-image-udif-segment)
- NDIF disk image[nb 1] (.ndif, .img, com.apple.disk-image-ndif); NDIF disk image segment (.imgpart, com.apple.disk-image-ndif-segment)
- self mounting image[nb 1] (.smi, com.apple.disk-image-smi)
- DVD/CD-R master image (.toast, .dvdr, .cdr, com.apple.disk-image-cdr, com.roxio.disk-image-toast)
- disk image segment (dmgpart)[2]
- Disk Copy 4.2 disk image[nb 1] (.dc42, .diskcopy42, com.apple.disk-image-dc42)
- DART disk image[nb 1] (.dart, com.apple.disk-image-dart)
- raw disk image (OSTypes: devr, hdrv, DDim, com.apple.disk-image-raw)
- PC drive container (OSTypes: OPCD, com.apple.disk-image-pc)
- ISO image (.iso, public.iso-image)
- sparse disk image (.sparseimage, com.apple.disk-image-sparse, .sparsebundle)
Notes[edit]
- ^ abcdMac OS Classic legacy disk image format supported by DiskImageMounter under Mac OS X versions 10.3—10.6[1] As of version 10.9, hdiutil can still convert these formats but unable to open or write them.
References[edit]
- ^ ab'hdiutil(1) Mac OS X Manual Page'. Apple Inc.Archived from the original on June 25, 2014. Retrieved September 3, 2014.
- ^ ab/System/Library/CoreServices/DiskImageMounter.app/Contents/Info.plist
See also[edit]
- Disk Copy - this program's predecessor.
- hdiutil - command line tool counterpart that ships with macOS
- FastDMG - free alternative replacement for DiskImageMounter
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