Is It Safe To Keep Dmg Files Mac
Dec 27, 2006 Well, after installation I tend to keep the.dmg file in the same folder where the application was installed. Then if the application is ever corrupted I can just delete it, and do a reinstallation from the.dmg without having to go back and download it again. I have two Macs with me: one is my personal, the other my office has given. Instead of downloading the installer twice (10 GB), It would be great to download the copy and once use it to upgrade multiple devices (iMacs/Mac minis). I have tried to find the dmg file but I haven't been able to find it, instead I was redirected to the App Store.
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The icon represents an internal hard drive within a generic file icon. | |
| Filename extension | .dmg, .smi, .img |
|---|---|
| Internet media type | application/x-apple-diskimage |
| Uniform Type Identifier (UTI) | com.apple.disk-image |
| Developed by | Apple Inc. |
| Type of format | 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.
- Some people create a “Games” directory, to keep games separate from other applications. But Applications is the most convenient place to put things, so we suggest you just put everything there. DMG files are mounted by your system, like a sort of virtual hard drive.
- Jan 12, 2008 If you're a Windows switcher, a.dmg is the same thing as an.iso file basically. It's a disk image. Mac appears to like to use image files for programs downloaded through the internet, while Windows usually use.zip files or direct.exe files. So I would say treat those.dmg files as you would.zip files in Windows.
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.
You can also seeThat being the case, it becomes essential to perform the conversion of this nature. Download dmg software. You can also seeWhat is a DMG to ISO Converter?A software is considered to be a DMG to ISO converter when it is able to turn DMG files to the ISO format. The DMG is used on the Mac platform while ISO is popular on the Windows platform. Typically, the software is easy to use, and the same is experienced when it comes to the conversion of files from DMG to ISO. Essentially, the two are the default disk image formats.
- 3File format
Features[edit]
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.
History[edit]
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).
Is It Safe To Keep Dmg Files Mac 2017
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.
Trailer[edit]
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 |
|---|---|---|
| 000 | 4 | Magic bytes ('koly'). |
| 004 | 4 | File version (current is 4) |
| 008 | 4 | The length of this header, in bytes. Should be 512. |
| 00C | 4 | Flags. |
| 010 | 8 | Unknown. |
| 018 | 8 | Data fork offset (usually 0, beginning of file) |
| 020 | 8 | Size of data fork (usually up to the XMLOffset, below) |
| 028 | 8 | Resource fork offset, if any |
| 030 | 8 | Resource fork length, if any |
| 038 | 4 | Segment number. Usually 1, may be 0 |
| 03C | 4 | Segment count. Usually 1, may be 0 |
| 040 | 16 | 128-bit GUID identifier of segment |
| 050 | 4 | Data fork checksum type |
| 054 | 4 | Data fork checksum size |
| 058 | 128 | Data fork checksum |
| 0D8 | 8 | Offset of XML property list in DMG, from beginning |
| 0E0 | 8 | Length of XML property list |
| 0E8 | 120 | Reserved bytes |
| 160 | 4 | Master checksum type |
| 164 | 4 | Master checksum size |
| 168 | 128 | Master checksum |
| 1E8 | 4 | Unknown, commonly 1 |
| 1EC | 8 | Size of DMG when expanded, in sectors |
| 1F4 | 12 | Reserved bytes (zeroes) |
Utilities[edit]
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]
References[edit]
Is It Safe To Keep Dmg Files Mac Os
- ^ abcdefg'hdiutil(1) Mac OS X Manual Page'. Archived from the original on 2016-05-14. Retrieved 2016-05-14.
- ^ ab'Mac OS X: Using Disk Copy disk image files'. Archived from the original on 2013-12-19. Retrieved 2013-04-25.
- ^
hdiutil(1)– Darwin and macOS General Commands Manual - ^'Re: Some apps refuse to launch in 10.2.8! (OT, but very important)'. Archived from the original on 2014-01-17.
- ^'Guides'. Apple. Archived from the original on 2009-03-06. Retrieved 2010-10-27.
- ^'DART 1.5.3: Version Change History'. Archived from the original on 2013-12-19. Retrieved 2013-04-25.
- ^'Software Downloads: Formats and Common Error Messages'. Archived from the original on 2010-12-24. Retrieved 2009-05-06.
- ^'VileFault'. 2006-12-29. Archived from the original on 2007-01-09. Retrieved 2010-10-27.
- ^Michael Tsai (2015-10-07). 'LZFSE Disk Images in El Capitan'. Archived from the original on 2017-04-09. Retrieved 2017-04-09.
- ^'Demystifying the DMG File Format'. Archived from the original on 2013-03-17.
- ^'dmg2img'. Archived from the original on 29 November 2010. Retrieved 2010-10-27.
- ^'DMGExtractor'. Archived from the original on 2011-01-02. Retrieved 2011-01-03.
- ^MacDrive Features / Boot Camp / System Requirements /. 'MacDrive Home page'. Mediafour. Archived from the original on 4 October 2010. Retrieved 2010-10-27.
- ^Olivia Dehaviland (2015-03-03). 'Apple DMG Disk Image Viewer'. DataForensics.org. Archived from the original on 2015-04-02. Retrieved 2015-03-10.
- ^'How To Convert DMG To ISO in Windows, Linux & Mac'. Archived from the original on 2010-03-07.
- ^'Convert DMG To ISO using PowerISO'. Archived from the original on 2009-05-02. Retrieved 2009-02-15.
- ^'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