1. Mac Opening Dmg Only Has Aliases In Mac
  2. Mac Opening Dmg Only Has Aliases Meaning
  3. Mac Opening Dmg Only Has Aliases 2

In Mac OSSystem 7 and later, an alias is a small file that represents another object in a local, remote, or removable[1]file system and provides a dynamic link to it; the target object may be moved or renamed, and the alias will still link to it (unless the original file is recreated; such an alias is ambiguous and how it is resolved depends on the version of macOS). In Windows, a 'shortcut', a file with a .lnk extension, performs a similar function.

It is similar to the Unixsymbolic link, but with the distinction of working even if the target file moves to another location on the same disk (in this case it acts like a hard link, but the source and target of the link may be on different filesystems, and the target of the link may be a directory). As a descendant of BSD, macOS supports Unix symbolic (and hard) links as well.

Function[edit]

An alias acts as a stand-in for any object in the file system, such as a document, an application, a folder, a hard disk, a network share or removable medium or a printer. When double-clicked, the computer will act the same way as if the original file had been double-clicked. Likewise, choosing an alias file from within a 'File Open' dialog box would open the original file. The purpose of an alias is to assist the user in managing large numbers of files by providing alternative ways to access them without having to copy the files themselves. While a typical alias under the classic Mac OS was small, between 1 and 5 KB, under macOS it can be fairly large, more than 5000 KB for the alias to a folder.

Preventing alias failure[edit]

An alias is a dynamic reference to an object. The original may be moved to another place within the same filesystem, without breaking the link. The operating system stores several pieces of information about the original in the resource fork of the alias file. Examples of the information used to locate the original are:

  • path
  • file ID
  • directory ID
  • name
  • file size

Since any of these properties can change without the computer's knowledge, as a result of user activity, various search algorithms are used to find the most plausible target. This fault-tolerance sets the alias apart from similar functions in some other operating systems, such as the Unixsymbolic link or the Microsoft Windowsshortcut, at the expense of increased complexity and unpredictability. For example, an application can be moved from one directory to another within the same filesystem, but an existing alias would still launch the same application when double-clicked.

Mac Opening Dmg Only Has Aliases In Mac

The question can arise of how an alias should work if a file is moved, and then a file is created with the same name as the original moved file, since the alias can be used to locate both the original name and the new location of the original file. With symbolic links the reference is unambiguous (soft links refer to the new file, hard links to the original). Before Mac OS X 10.2, however, such an ambiguous alias would consistently find the original moved file, rather than the recreated file. In Mac OS X 10.2 and later releases, the new file is found, matching the behaviour of symbolic links [1]. macOS applications can programmatically use the old behavior if required.

May 23, 2013 In response to hotwheels22. When you download software for the Mac it usually arrives as either a.dmg or.zip file. If you double-click on the.dmg file it 'mounts' on your Desktop with a disk icon. Sometimes a Finder window opens automatically, sometimes it doesn't and you have to double-click on the disk icon.

Aliases are similar in operation to shadows in the graphical Workplace Shell of the OS/2 operating system.

Dmg

Distinguishing marks[edit]

In System 7 through Mac OS 9, aliases distinguished themselves visually to the user by the fact that their file names were in italics. To accommodate languages that don't have italics (such as Japanese), in Mac OS 8.5 another distinguishing mark was added, badging with an 'alias arrow'—a black arrow with a small white border—similar to that used for shortcuts in Microsoft Windows.

In macOS, the filenames of aliases are not italicized, but the arrow badge remains.

File structure[edit]

  • Open DMG File on Mac OS Since DMG is a native Mac OS disk image format opening DMG file is as easy as double clicking on it in Finder. When you open DMG file this way, disk image stored inside DMG file will be mounted, and then opened in a separate Finder window.
  • Nov 18, 2019  Again, just because you can extract a DMG file in Windows, or even convert a DMG to a Windows-readable format, doesn't always mean that the contents of the DMG file will suddenly become compatible with Windows. The only way to use a Mac program or a Mac video game in Windows is to download the Windows-equivalent version.
  • Nov 18, 2019 DMG files are for Mac and EXE files are for Windows, so the only way to use a DMG program on Windows is to download its equivalent from the developer (if one exists); there aren't any DMG file to EXE file converters.
  • Sep 19, 2018  To make aliases of macOS Unix commands in your bash or zsh shell on macOS and earlier versions, it is done via your.bashprofile or.zsh file which lives in your home account directory, if the file does not already exist, just create one. As of macOS 10.6 Catalina, Apple has made the zsh shell the default shell, previously it was the bash shell.
  • Aside from the Finder application, you can open DMG files through Apple Disk Utility, Roxio Toast, and Dare to be Creative iArchiver for Mac platform. On the other hand, additional applications such Acute Systems TransMac, DMG2IMG, and DMG2ISO can be installed on Windows to fully support the files.

The alias files in macOS start by the magic number62 6F 6F 6B 00 00 00 00 6D 61 72 6B 00 00 00 00 which is in ASCIIbook␀␀␀␀mark␀␀␀␀ (␀ representing the Null character).

Following the magic number, it has been reported that an alias has a set of records inside it, each record is 150 bytes long and consists of the fields shown below.[2] However, alias files are far larger than this would explain, and include other information at least including icons.[3][4]

  1. 4 bytes user type name/app creator code = long ASCII text string (none = 0)
  2. 2 bytes record size = short unsigned total length
  3. 2 bytes record version = short integer version (current version = 2)
  4. 2 bytes alias kind = short integer value (file = 0; directory = 1)
  5. 1 byte volume name string length = byte unsigned length
  6. 27 bytes volume name string (if volume name string < 27 chars then pad with zeros)
  7. 4 bytes volume created mac date = long unsigned value in seconds since beginning 1904 to 2040
  8. 2 bytes volume signature = short unsigned HFS value
  9. 2 bytes volume type = short integer mac os value (types are Fixed HD = 0; Network Disk = 1; 400kB FD = 2;800kB FD = 3; 1.4MB FD = 4; Other Ejectable Media = 5 )
  10. 4 bytes parent directory id = long unsigned HFS value
  11. 1 bytes file name string length = byte unsigned length
  12. 63 bytes file name string (if file name string < 63 chars then pad with zeros)
  13. 4 bytes file number = long unsigned HFS value
  14. 4 bytes file created mac date = long unsigned value in seconds since beginning 1904 to 2040
  15. 4 bytes file type name = long ASCII text string
  16. 4 bytes file creator name = long ASCII text string
  17. 2 bytes nlvl From (directories from alias thru to root) = short integer range
  18. 2 bytes nlvl To (directories from root thru to source) = short integer range (if alias on different volume then set above to -1)
  19. 4 bytes volume attributes = long hex flags
  20. 2 bytes volume file system id = short integer HFS value
  21. 10 bytes reserved = 80-bit value set to zero
  22. 4+ bytes optional extra data strings = short integer type + short unsigned string length (types are Extended Info End = -1; Directory Name = 0; Directory IDs = 1; Absolute Path = 2; AppleShare Zone Name = 3; AppleShare Server Name = 4; AppleShare User Name = 5; Driver Name = 6; Revised AppleShare info = 9; AppleRemoteAccess dialup info = 10)
  23. string data = hex dump
  24. odd lengths have a 1 byte odd string length pad = byte value set to zero

Alias record structure outside of size length[edit]

The following is for use with the Apple's Alias Resource Manager.

  1. 4 bytes resource type name = long ASCII text string
  2. 2 bytes resource ID = short integer value
  3. 2 bytes resource end pad = short value set to zero

Java code to flag an alias file

Managing aliases[edit]

In System 7, the only way to create an alias was to select the original and choose 'Make Alias' from the 'File' menu. An alias, with the same name and ' alias' appended would then be created in the same folder. In later versions, it became possible to create aliases by drag-and-drop, while holding down the command and option modifier keys.

Mac OS 8.5 added a feature for re-connecting aliases that had been broken for one reason or another (when the simple search algorithms failed to find a reliable replacement). This was done by selecting a new target through the standard Open File dialog.

In Mac OS 8.5 options were added for command-optiondragging an object in the Finder to create an alias at that location. This is where the alias cursor was added to the system. The cursor mirrors the appearance of the 'create shortcut' cursor on Windows systems.

Relation to BSD symbolic and hard links[edit]

Unix and similar operating systems provide 2 features very similar to macOS aliases: symbolic links and hard links. When using the macOS Finder, links are displayed and treated largely like macOS aliases, and even carry an identical 'Kind' attribute. However, when using the shell command line, macOS aliases are not recognized: for example, you cannot use the cd command with the name of an alias file. This is because an alias is implemented as a file on the disk that must be interpreted by an API while links are implemented within the filesystem and are thus functional at any level of the OS.

There is currently no pre-installed command to resolve an alias to the path of the file or directory it refers to. However, a freely available C program makes use of the Mac Carbon APIs to perform this task.[5] Given that, commands such as cd can be set up to check for aliases and treat them just like symbolic or hard links.

References[edit]

  1. ^Files: Chapter 4 - Alias Manager; Search Strategies — Inside Macintosh developer documentation
  2. ^Some information about MacOS aliases collected from the web. (reverse engineering effort)
  3. ^Forum discussion of the large size of aliases.
  4. ^'Further details, including changes with various Mac OS versions'. Archived from the original on 2013-04-30. Retrieved 2018-10-11.
  5. ^Davis, Thos. 'getTrueName.c'. Mac OS X Hints. IDG. Retrieved 24 October 2016.

Mac Opening Dmg Only Has Aliases Meaning

External links[edit]

  • Alias Manager Reference — Inside Macintosh developer documentation
  • System 7 aliases — Article about System 7 aliases, from 1992


Retrieved from 'https://en.wikipedia.org/w/index.php?title=Alias_(Mac_OS)&oldid=931313045'

Open DMG File

DMG is used for disk image files on Macintosh computers running Mac OS X. This file extension replaces the older file extension IMG which was discontinued during the release of later series of Mac operating systems. You can open DMG file on Mac, Linux, and Windows operating systems but it will require additional software to be installed on Windows. Note that on Windows and Linux you cannot open every DMG file, since there are certain software limitations on DMG format variation.

DMG files are used by Apple for software distribution over the internet. These files provide features such as compression and password protection which are not common to other forms of software distribution file formats. DMG files are native to Mac OS X and are structured according to Universal Disk Image Format (UDIF) and the New Disk Image Format (NDIF). They can be accessed through the Mac OS Finder application by either launching the DMG file or mounting it as a drive.

DMG is also referred to as the Apple’s equivalent to MSI files in Windows PC. Non-Macintosh systems may access DMG files and extract or convert them to ISO image files for burning. Several applications are designed to offer this solution for Windows systems.

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7-Zip and DMG Extractor are the best options to open DMG file on Windows because they are compatible with the most DMG variations. For Linux a built-in 'cdrecord' command can be issued to burn DMG files to CD's or DVD's.

Aside from the Finder application, you can open DMG files through Apple Disk Utility, Roxio Toast, and Dare to be Creative iArchiver for Mac platform. On the other hand, additional applications such Acute Systems TransMac, DMG2IMG, and DMG2ISO can be installed on Windows to fully support the files.

Mac Opening Dmg Only Has Aliases 2

Read how you can open DMG files on Mac OS, Windows and Linux.

DMG files are transferred over e-mail or internet using application/x-apple-diskimage multipurpose internet mail extensions (MIME) type.

Following file types are similar to DMG and contain disk images:

  • ISO File - ISO disk image file
  • IMG File - IMG disk image file
  • VHD/VHDX File - Virtual Hard Drive image file