computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes, and development of both hardware and software. Computing has scientific, e ...

, a symbolic link (also symlink or soft link) is a file whose purpose is to point to a file or directory (called the "target") by specifying a

path A path is a route for physical travel – see Trail. Path or PATH may also refer to: Physical paths of different types * Bicycle path * Bridle path, used by people on horseback * Course (navigation), the intended path of a vehicle * Desire p ...

thereto. Symbolic links are supported by

POSIX The Portable Operating System Interface (POSIX) is a family of standards specified by the IEEE Computer Society for maintaining compatibility between operating systems. POSIX defines both the system- and user-level application programming interf ...

and by most

Unix-like A Unix-like (sometimes referred to as UN*X or *nix) operating system is one that behaves in a manner similar to a Unix system, although not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Unix-li ...

operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also in ...

s, such as

FreeBSD FreeBSD is a free and open-source Unix-like operating system descended from the Berkeley Software Distribution (BSD), which was based on Research Unix. The first version of FreeBSD was released in 1993. In 2005, FreeBSD was the most popular ...

Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, which ...

, and

macOS macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac computers. Within the market of desktop and lapt ...

. Limited support also exists in

Windows 7 Windows 7 is a major release of the Windows NT operating system developed by Microsoft. It was released to manufacturing on July 22, 2009, and became generally available on October 22, 2009. It is the successor to Windows Vista, released nearly ...

and

Windows Vista Windows Vista is a major release of the Windows NT operating system developed by Microsoft. It was the direct successor to Windows XP, which was released five years before, at the time being the longest time span between successive releases of ...

, and to some degree in

Windows 2000 Windows 2000 is a major release of the Windows NT operating system developed by Microsoft and oriented towards businesses. It was the direct successor to Windows NT 4.0, and was Software release life cycle#Release to manufacturing (RTM), releas ...

and

Windows XP Windows XP is a major release of Microsoft's Windows NT operating system. It was released to manufacturing on August 24, 2001, and later to retail on October 25, 2001. It is a direct upgrade to its predecessors, Windows 2000 for high-end and ...

in the form of shortcut files. CTSS on

IBM 7090 The IBM 7090 is a second-generation transistorized version of the earlier IBM 709 vacuum tube mainframe computer that was designed for "large-scale scientific and technological applications". The 7090 is the fourth member of the IBM 700/7000 se ...

had files linked by name in 1963. By 1978 minicomputer operating systems from DEC, and in Data General's RDOS included symbolic links.

Overview

A symbolic link contains a text string that is automatically interpreted and followed by the operating system as a path to another file or directory. This other file or directory is called the "target". The symbolic link is a second file that exists independently of its target. If a symbolic link is deleted, its target remains unaffected. If a symbolic link points to a target, and sometime later that target is moved, renamed or deleted, the symbolic link is not automatically updated or deleted, but continues to exist and still points to the old target, now a non-existing location or file. Symbolic links pointing to moved or non-existing targets are sometimes called ''broken'', ''orphaned'', ''dead'', or ''dangling''. Symbolic links are different from hard links. Hard links do not link paths on different

volumes Volume is a measure of occupied three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch). The defi ...

file system In computing, file system or filesystem (often abbreviated to fs) is a method and data structure that the operating system uses to control how data is stored and retrieved. Without a file system, data placed in a storage medium would be one larg ...

s, whereas symbolic links may point to any file or directory irrespective of the volumes on which the link and target reside. Hard links always refer to an existing file, whereas symbolic links may contain an arbitrary path that does not point to anything. Symbolic links operate transparently for many operations: programs that read or write to files named by a symbolic link will behave as if operating directly on the target file. However, they have the effect of changing an otherwise hierarchic filesystem from a

tree In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are ...

into a directed graph, which can have consequences for such simple operations as determining the current directory of a process. Even the Unix standard for navigating to a directory's parent directory no longer works reliably in the face of symlinks. Some shells

heuristic A heuristic (; ), or heuristic technique, is any approach to problem solving or self-discovery that employs a practical method that is not guaranteed to be optimal, perfect, or rational, but is nevertheless sufficient for reaching an immediate, ...

ally try to uphold the illusion of a tree-shaped hierarchy, but when they do, this causes them to produce different results from other programs that manipulate pathnames without such heuristic, relying on the operating system instead. Programs that need to handle symbolic links specially (e.g., shells and backup utilities) thus need to identify and manipulate them directly. Some Unix as well as Linux distributions use symbolic links extensively in an effort to reorder the file system hierarchy. This is accomplished with several mechanisms, such as variant, context-dependent symbolic links. This offers the opportunity to create a more intuitive or application-specific

directory tree In computing, a directory is a file system cataloging structure which contains references to other computer files, and possibly other directories. On many computers, directories are known as folders, or drawers, analogous to a workbench or the t ...

and to reorganize the system without having to redesign the core set of system functions and utilities.

POSIX and Unix-like operating systems

-compliant operating systems, symbolic links are created with the symlink system call. The ln shell command normally uses the link system call, which creates a hard link. When the ln ''-s'' flag is specified, the symlink() system call is used instead, creating a symbolic link. Symlinks were introduced in 4.1c.1 BSD Unix from

U.C. Berkeley The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California) is a public land-grant research university in Berkeley, California. Established in 1868 as the University of California, it is the state's first land-grant univ ...

. The following command creates a symbolic link at the

command-line interface A command-line interpreter or command-line processor uses a command-line interface (CLI) to receive commands from a user in the form of lines of text. This provides a means of setting parameters for the environment, invoking executables and pro ...

(shell):

 ln -s target_path link_path

is the relative or absolute path to which the symbolic link should point. Usually the target will exist, although symbolic links may be created to non-existent targets. is the path of the symbolic link. After creating the symbolic link, some operations can be used to treat it as an alias for the target. However, the lstat, lchown and readlink operations are unique to symbolic links and do not apply to the target; by using those system calls, programs that examine the file system (e.g., ls,

find 
Find, FIND or Finding may refer to:
 Computing
*  find (Unix), a command on UNIX platforms
* find (Windows), a command on DOS/Windows platforms
 Books
* ''The Find'' (2010), by  Kathy Page
* ''The Find'' (2014), by William Hope Hodgson

 Film and t ...

) can report on symbolic links (instead of their targets, if any). Because the rename and

unlink 




In the mathematics, mathematical field of knot theory, an unlink is a Link (knot theory), link that is equivalent (under ambient isotopy) to finitely many disjoint circles in the plane.
  Properties 
* An ''n''-component link ''L'' ⊂&nbs ...

system calls are coded to operate directly on symbolic links, file system management commands (e.g., rm, mv) affect the symbolic link itself (instead of being applied to the symbolic link target, if any). The rm (delete file) command removes the link itself, not the target file. Likewise, the mv command moves or renames the link, not the target. The cp command has options that allow either the symbolic link or the target to be copied. Commands which read or write file contents will access the contents of the target file. The POSIX directory listing application, ls, denotes symbolic links with an arrow after the name, pointing to the name of the target file (see following example), when the long directory list is requested (-l option). When a directory listing of a symbolic link that points to a directory is requested, only the link itself will be displayed. In order to obtain a listing of the linked directory, the path must include a trailing directory separator character ('/', slash). Note: In the example below do not create "three" directory before creation of link in /tmp directory. $ mkdir -p /tmp/one/two $ echo "test_a" >/tmp/one/two/a $ echo "test_b" >/tmp/one/two/b $ cd /tmp/one/two $ ls -l -rw-r--r-- 1 user group 7 Jan 01 10:01 a -rw-r--r-- 1 user group 7 Jan 01 10:01 b $ cd /tmp $ ln -s /tmp/one/two three $ ls -l three lrwxrwxrwx 1 user group 12 Jul 22 10:02 /tmp/three -> /tmp/one/two $ ls -l three/ -rw-r--r-- 1 user group 7 Jan 01 10:01 a -rw-r--r-- 1 user group 7 Jan 01 10:01 b $ cd three $ ls -l -rw-r--r-- 1 user group 7 Jan 01 10:01 a -rw-r--r-- 1 user group 7 Jan 01 10:01 b $ cat a test_a $ cat /tmp/one/two/a test_a $ echo "test_c" >/tmp/one/two/a $ cat /tmp/one/two/a test_c $ cat a test_c

Storage of symbolic links

Early implementations of symbolic links stored the symbolic link information as data in regular files. The file contained the textual reference to the link's target, and the file mode bits indicated that the type of the file is a symbolic link. This method was slow and an inefficient use of disk-space on small systems. An improvement, called fast symlinks, allowed storage of the target path within the

data structure In computer science, a data structure is a data organization, management, and storage format that is usually chosen for efficient access to data. More precisely, a data structure is a collection of data values, the relationships among them, a ...

s used for storing file information on disk (

inode The inode (index node) is a data structure in a Unix-style file system that describes a file-system object such as a file or a directory. Each inode stores the attributes and disk block locations of the object's data. File-system object attribute ...

s). This space normally stores a list of disk

block Block or blocked may refer to: Arts, entertainment and media Broadcasting * Block programming, the result of a programming strategy in broadcasting * W242BX, a radio station licensed to Greenville, South Carolina, United States known as ''96.3 ...

addresses allocated to a file. Thus, symlinks with short target paths are accessed quickly. Systems with fast symlinks often fall back to using the original method if the target path exceeds the available inode space. The original style is retroactively termed a slow symlink. It is also used for disk compatibility with other or older versions of operating systems. Although storing the link value inside the inode saves a disk block and a disk read, the operating system still needs to parse the path name in the link, which always requires reading additional inodes and generally requires reading other, and potentially many, directories, processing both the list of files and the inodes of each of them until it finds a match with the link's path components. Only when a link points to a file in the same directory do "fast symlinks" provide significantly better performance than other symlinks. The vast majority of POSIX-compliant implementations use fast symlinks. However, the

standard does not require the entire set of file status information common to regular files to be implemented for symlinks. This allows implementations to use other solutions, such as storing symlink data in directory entries. The

file system permissions Most file systems include attributes of files and directories that control the ability of users to read, change, navigate, and execute the contents of the file system. In some cases, menu options or functions may be made visible or hidden depending ...

of a symbolic link are not used; the access modes of the target file are controlled by the target file's own permissions. Some operating systems, such as FreeBSD, offer the ability to modify file permissions and filesystem attributes of a symbolic link, through lchmod and lchflags system calls respectively. The reported size of a symlink is the number of characters in the path it points to.

Error handling

A traditional

Unix filesystem In Unix and operating systems inspired by it, the file system is considered a central component of the operating system. It was also one of the first parts of the system to be designed and implemented by Ken Thompson in the first experimental ...

has a tree structure, however symbolic links allow it to contain loops.

Microsoft Windows

NTFS symbolic link

NTFS New Technology File System (NTFS) is a proprietary journaling file system developed by Microsoft. Starting with Windows NT 3.1, it is the default file system of the Windows NT family. It superseded File Allocation Table (FAT) as the preferred fil ...

3.1 introduced support for symbolic links for any type of file. It was included with

, but was only enabled by default for kernel mode programs;

and later versions of Windows enabled support for symbolic links to user mode applications, as well, and supplied the command line utility mklink for creating them. Third-party drivers are required to enable support for NTFS symbolic links in Windows XP. Unlike

junction point The NTFS file system defines various ways to redirect files and folders, e.g., to make a file point to another file or its contents without making a copy of it. The object being pointed to is called the target. Such file is called a hard or symbo ...

s, a symbolic link can also point to a file or remote

Server Message Block Server Message Block (SMB) is a communication protocol originally developed in 1983 by Barry A. Feigenbaum at IBM and intended to provide shared access to files and printers across nodes on a network of systems running IBM's OS/2. It also provides ...

(SMB) network path. Additionally, the NTFS symbolic link implementation provides full support for cross-filesystem links. However, the functionality enabling cross-host symbolic links requires that the remote system also support them. Symbolic links are designed to aid in migration and application compatibility with

operating systems. Microsoft aimed for Windows Vista's symbolic links to "function just like UNIX links". However, the implementation differs from Unix symbolic links in several ways. For example, Windows Vista users must manually indicate when creating a symbolic link whether it is a file or a directory. Windows 7 and Vista support a maximum of 31

reparse point An NTFS reparse point is a type of NTFS file system object. It is available with the NTFS v3.0 found in Windows 2000 or later versions. Reparse points provide a way to extend the NTFS filesystem. A reparse point contains a reparse tag and data that ...

s (and therefore symbolic links) for a given path (i.e. any given path can have at most 31 indirections before Windows gives up). Only users with the new ''Create Symbolic Link'' privilege, which only administrators have by default, can create symbolic links. If this is not the desired behavior, it must be changed in the Local Security Policy management console. Additionally, NTFS symbolic links to files are distinct from NTFS symbolic links to directories and therefore cannot be used interchangeably, unlike on POSIX where the same symbolic link can refer to either files or directories. In Windows Vista and later, when the working directory path ends with a symbolic link, the current parent path reference, , will refer to the parent directory of the symbolic link rather than that of its target. This behaviour is also found at the shell level in at least some POSIX systems, including

, but never in accessing files and directories through operating system calls. For instance, bash builtin commands and operate on the current logical directory. is often used in scripts to determine the actual current working directory. When any path is used with a system call, any use of will use the actual filesystem parent of the directory containing the pseudo-directory entry. So, and may return completely different results.

Examples

# PS > mklink /D "$env:LOCALAPPDATA\Plex Media Server" "G:\Plex Media Server" # PS > New-Item -Path C:\TargetPath -ItemType SymbolicLink -Value F:\SourcePath

NTFS junction points

The

version of

introduced reparse points, which enabled, among other things, the use of

Volume Mount Point NTFS volume mount points are specialized NTFS filesystem objects which are used to mount and provide an entry point to other volumes. Description NTFS volume mount points are NTFS filesystem objects—implemented as NTFS reparse points—whi ...

s and junction points. Junction points are for directories only, and moreover, local directories only; junction points to remote shares are unsupported. The Windows 2000 and XP Resource Kits include a program called ' to create junction points; a more powerful one named ''Junction'' was distributed by

Sysinternals Windows Sysinternals is a website that offers technical resources and utilities to manage, diagnose, troubleshoot, and monitor a Microsoft Windows environment. Originally, the Sysinternals website (formerly known as ntinternals) was created in 19 ...

Mark Russinovich Mark Eugene Russinovich (born December 22, 1966) is a Spanish-born American software engineer and author who serves as CTO of Microsoft Azure. He was a cofounder of software producers Winternals before it was acquired by Microsoft in 2006. Ea ...

. Not all standard applications support reparse points. Most noticeably, Backup suffers from this problem and will issue an error message 0x80070003 when the folders to be backed up contain a reparse point.

Shortcuts

Shortcuts, which are supported by the graphical file browsers of some operating systems, may resemble symbolic links but differ in a number of important ways. One difference is what type of software is able to follow them: * Symbolic links are automatically resolved by the file system. Any software program, upon accessing a symbolic link, will see the target instead, whether the program is aware of symbolic links or not. * Shortcuts are treated like ordinary files by the file system and by software programs that are not aware of them. Only software programs that understand shortcuts (such as the Windows shell and file browsers) treat them as references to other files. Another difference are the capabilities of the mechanism: *

Microsoft Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for serv ...

shortcuts normally refer to a destination by an absolute path (starting from the root directory), whereas POSIX symbolic links can refer to destinations via either an absolute or a

relative path A path is a string of characters used to uniquely identify a location in a directory structure. It is composed by following the directory tree hierarchy in which components, separated by a delimiting character, represent each directory. The del ...

. The latter is useful if both the symlink and its target share some common ancestor path which is not known at creation (e.g., in an

archive file In computing, an archive file is a computer file that is composed of one or more files along with metadata. Archive files are used to collect multiple data files together into a single file for easier portability and storage, or simply to compre ...

that can be unpacked anywhere). * Microsoft Windows application shortcuts contain additional metadata that can be associated with the destination, whereas POSIX symbolic links are just strings that will be interpreted as absolute or relative pathnames. * Unlike symbolic links, Windows shortcuts maintain their references to their targets even when the target is moved or renamed. Windows domain clients may subscribe to a

Windows service In Windows NT operating systems, a Windows service is a computer program that operates in the background. It is similar in concept to a Unix daemon. A Windows service must conform to the interface rules and protocols of the Service Control Manage ...

called
Distributed Link Tracking
' to track the changes in files and folders to which they are interested. The service maintains the integrity of shortcuts, even when files and folders are moved across the network. Additionally, in Windows 9x and later,

Windows shell The Windows shell is the graphical user interface for the Microsoft Windows operating system. Its readily identifiable elements consist of the desktop, the taskbar, the Start menu, the task switcher and the AutoPlay feature. On some versions of W ...

tries to find the target of a broken shortcut before proposing to delete it.

Folder shortcuts

Almost like shortcuts, but transparent to the Windows shell. They are implemented as ordinary folders (which need to have the ''read only'' and/or ''system'' attribute) containing a shortcut named ''target.lnk'' which refers to the target and a (hidden) ''desktop.ini'' with (at least) the following contents: ShellClassInfo CLSID2= Folder shortcuts are created and used from the Windows shell in the ''network neighborhood'' for example.

Shell objects

The ''shell objects'' or ''shell folders'' are defined in the Windows registry and can be used to implement a sort of symbolic link too. Like folder shortcuts, they are transparent to the Windows shell. A minimal implementation is (the CLSID ' is used as a placeholder): KEY_CLASSES_ROOT\CLSID\ @="display name" KEY_CLASSES_ROOT\CLSID\\DefaultIcon @="..." ; path to icon KEY_CLASSES_ROOT\CLSID\\InProcServer32 @="%SystemRoot%\\System32\\ShDocVw.Dll" "ThreadingModel"="Apartment" KEY_CLASSES_ROOT\CLSID\\Instance "CLSID"="" KEY_CLASSES_ROOT\CLSID\\Instance\InitPropertyBag "Attributes"=hex:15,00,00,00 "Target"="..." ; absolute (WITHOUT "TargetKnownFolder" or "TargetSpecialFolder" only) ; or relative path to target "TargetKnownFolder"="" ; GUID of target folder, Windows Vista and later "TargetSpecialFolder"="0x00xy" ; CSIDL of target KEY_CLASSES_ROOT\CLSID\\ShellFolder "Attributes"=hex:00,00,00,00 The ''My Documents'' folder on the ''Desktop'' as well as the ''Fonts'' and the ''Administrative Tools'' folders in the ''Control Panel'' are examples of ''shell objects'' redirected to file-system folders.

Cygwin symbolic links

Cygwin simulates POSIX-compliant symbolic links in the Microsoft Windows file system. It uses identical programming and user utility interfaces as Unix (see above), but creates Windows shortcuts (.lnk files) with additional information used by Cygwin at the time of symlink resolution. Cygwin symlinks are compliant with the POSIX standard in terms of how they are resolved, and with Windows standards in terms of their on-disk representation. Additionally, Cygwin can be set up to support native Windows symbolic links which can be used out of Cygwin without restrictions. This requires: # Changing the CYGWIN environment variable to contain ; # Running the Cygwin with elevated rights because Windows restricts the creation of symbolic links to privileged users Some differences exist, however. Cygwin has no way to specify shortcut-related information – such as working directory or icon – as there is no place for such parameters in ln -s command. To create standard Microsoft .lnk files Cygwin provides the mkshortcut and readshortcut utilities. The Cygwin User's Guide has more information on this topic.

MSYS2 Mingw-w64 is a free and open source software development environment to create ( cross-compile) Microsoft Windows PE applications. It was forked in 2005–2010 from MinGW (''Minimalist GNU for Windows''). Mingw-w64 includes a port of the GNU C ...

, which is based on Cygwin, has a similar set of settings but defaults to copying the files.

Comparison of POSIX and Windows symbolic links

Other implementations

Implementations of features similar to symbolic links.

Early MIT

MIT The Massachusetts Institute of Technology (MIT) is a private land-grant research university in Cambridge, Massachusetts. Established in 1861, MIT has played a key role in the development of modern technology and science, and is one of the m ...

Compatible Time-Sharing System The Compatible Time-Sharing System (CTSS) was the first general purpose time-sharing operating system. Compatible Time Sharing referred to time sharing which was compatible with batch processing; it could offer both time sharing and batch proces ...

c. 1963 and

Incompatible Timesharing System Incompatible Timesharing System (ITS) is a time-sharing operating system developed principally by the MIT Artificial Intelligence Laboratory, with help from Project MAC. The name is the jocular complement of the MIT Compatible Time-Sharing Sy ...

both have linked files where the name of the target file is specified in a directory entry.

Amiga

The command creating symbolic links is makelink, which is also used for hard links. Internally the dos.library returns an error code indicating that a target is a soft link if you try to perform actions on it that are only legal for a file, and applications that wish to follow the symbolic link then needs to explicitly make a call to follow the link and retry the operation. The AmigaDOS shell will follow links automatically.

Mac OS

In Mac OS, applications or users can also employ ''

aliases A pseudonym (; ) or alias () is a fictitious name that a person or group assumes for a particular purpose, which differs from their original or true name ( orthonym). This also differs from a new name that entirely or legally replaces an individu ...

'', which have the added feature of following the target, even if it is moved to another location on the same volume. This is not to be confused with the shell command

alias Alias may refer to: * Pseudonym * Pen name * Nickname Arts and entertainment Film and television * ''Alias'' (2013 film), a 2013 Canadian documentary film * ''Alias'' (TV series), an American action thriller series 2001–2006 * ''Alias the ...

OS/2

In the

OS/2 OS/2 (Operating System/2) is a series of computer operating systems, initially created by Microsoft and IBM under the leadership of IBM software designer Ed Iacobucci. As a result of a feud between the two companies over how to position OS/2 ...

operating system, symbolic links somewhat resemble

shadows A shadow is a dark area where light from a light source is blocked by an opaque object. It occupies all of the three-dimensional volume behind an object with light in front of it. The cross section of a shadow is a two-dimensional silhouette, ...

in the graphical

Workplace Shell The Workplace Shell (WPS) is an object-oriented desktop shell (also called desktop environment) produced by IBM's Boca Raton development lab for OS/2 2.0. It is based on Common User Access and made a radical shift away from the Program Manager ...

. However, shadows, due to the fully object-oriented System Object Model, are considerably more powerful and robust than a simple link. For example, shadows do not lose their capabilities when renamed or when either the object or subject of the link is relocated.

Variable symbolic links

Symbolic links may be implemented in a context-dependent or variable fashion, such that the link points to varying targets depending on a configuration parameter, run-time parameter, or other instantaneous condition. A ''variable'' or ''variant symbolic link'' is a symbolic link that has a variable name embedded in it. This allows some flexibility in filesystem order that is not possible with a standard symbolic link. Variables embedded in a symbolic link may include user and environment specific information.

Operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also in ...

s that make use of variant symbolic links include

NetBSD NetBSD is a free and open-source Unix operating system based on the Berkeley Software Distribution (BSD). It was the first open-source BSD descendant officially released after 386BSD was forked. It continues to be actively developed and is a ...

DragonFly BSD DragonFly BSD is a free and open-source Unix-like operating system forked from FreeBSD 4.8. Matthew Dillon, an Amiga developer in the late 1980s and early 1990s and FreeBSD developer between 1994 and 2003, began working on DragonFly BSD in Ju ...

Domain/OS Domain/OS is the discontinued operating system used by the Apollo/Domain line of workstations manufactured by Apollo Computer. It was originally launched in 1981 as AEGIS, and was rebranded to Domain/OS in 1988 when Unix environments were added to ...

Tru64 Tru64 UNIX is a discontinued 64-bit UNIX operating system for the Alpha instruction set architecture (ISA), currently owned by Hewlett-Packard (HP). Previously, Tru64 UNIX was a product of Compaq, and before that, Digital Equipment Corporation (DE ...

uses a ''context dependent symbolic link'' where the context is the cluster member number.

Pyramid Technology Pyramid Technology Corporation was a computer company that produced a number of RISC-based minicomputers at the upper end of the performance range. It was based in the San Francisco Bay Area of California They also became the second company to s ...

's OSx

Operating System An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also in ...

implemented ''conditional symbolic links'' which pointed to different locations depending on which

universe The universe is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy. The Big Bang theory is the prevailing cosmological description of the development of the universe. Acc ...

a program was running in. The universes supported were AT&Ts's SysV.3 and the Berkeley Software Distribution (BSD 4.3). For example: if the ps command was run in the ''att'' universe, then the symbolic link for the directory ''/bin'' would point to ''/.attbin'' and the program ''/.attbin/ps'' would be executed. Whereas if the ps command was run in the ''ucb'' universe, then ''/bin'' would point to ''/.ucbbin'' and ''/.ucbbin/ps'' would be executed. Similar Conditional Symbolic Links were also created for other directories such as ''/lib'', ''/usr/lib'', ''/usr/include''.

References

External links

Q & A: The difference between hard and soft links
as applied to Linux
Junction
maintain NTFS junction points (for Windows 2000 and above)
FSUtil Hardlink
Microsoft Technet page on using the command-line tool FSUtil to create hardlinks (for Windows 2000 and above)

: file system drivers to enable Symbolic Links for Windows XP (also mirrored on Link Shell Extension site). Sources available. {{Computer files Computer file systems Unix file system technology