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Encyclopedia > NTFS junction point

An NTFS junction point (JP) is a feature of the NTFS file system version 3.0 or later. It is a type of NTFS reparse point. Junction Points can be used in a similar way to symbolic links — allowing the creation of a link to a folder that is, for most intents and purposes, the same as the folder itself. This has many benefits over a Windows shell shortcut (.lnk) file, such as allowing you to access files within the shortcut via explorer, the console, etc. NTFS is the standard file system of Windows NT, including its later versions Windows 2000, Windows XP, Windows Server 2003, and Windows Vista. ... In computing, a file system (often also written as filesystem) is a method for storing and organizing computer files and the data they contain to make it easy to find and access them. ... An NTFS reparse point (JP) is a type of NTFS file system object. ... In computing, a symbolic link (often shortened to symlink and also known as a soft link) consists of a special type of file that serves as a reference to another file. ...


Junction points can only link to folders and volumes. You can create a similar link to a file, but with the restriction that the file must belong to the same logical volume, using hard links. In computing, a hard link is a reference, or pointer, to physical data on a storage volume. ...

Contents

Warning

  • Microsoft strongly recommends:
    • Use NTFS ACLs to protect junction points from inadvertent deletion.
    • Use NTFS ACLs to protect files and directories targeted by junction points from inadvertent deletion or other file system operations.
    • Never delete a junction point using Explorer, a del /s command, or other file system utilities that walk recursively into directory trees. These utilities will affect the target directory and all subdirectories. Instead, use the utilities described below to delete junction points.
    • Use caution when applying ACLs or changing file compression in a directory tree that includes NTFS Junction Points.
    • Do not create namespace cycles with NTFS or DFS junction points.
    • Place all your junction points at a secure location in a namespace where you can test them out in safety, and other users will not mistakenly delete them or walk through them.
  • Obscure: There are issues relating to junction points on MS Windows 2000 domain controllers & certain Active Directory files.[1]

Microsoft Corporation, (NASDAQ: MSFT, HKSE: 4338) is a multinational computer technology corporation with global annual revenue of US$44. ... NTFS is the standard file system of Windows NT, including its later versions Windows 2000, Windows XP, Windows Server 2003, and Windows Vista. ... In computer security, an access control list (ACL) is a list of permissions attached to an object. ...

Examples of use

Program redirection

By setting a JP that points to a directory containing a particular version of a piece of software, you can, in most cases, seamlessly add another version of the software and redirect the JP to point to the version you wish to use.

Space saving

If you are running out of space on a drive, you can move those files to a new drive - but this can cause some problems with old links, configuration files, registry, etc. By creating a JP at the previous location (pointing to the new location) Windows will treat it the same as if the directory still exists there, redistributing the load to the filesystem with more space.

Convenience

To avoid issues caused by the space in directory names such as C:Program Files, a link, such as C:Progs can be created. This can simplify the command line. Similarly, C:MyDocs could be created to redirect to C:Documents and SettingsUsernameMy Documents.

Drive letters

In a corporate environment, the users can easily run out of drive letters. Nowadays lots of people have all sorts of extra drives locally from flash card readers and USB devices. Adding that to the fact that alot of companies have a few network drives on all users computer, makes junction points a perfect solution for making one network drive for each person and just setting up junction points on the server to make the right folders available for them from there.

Issues

Often it is difficult to delete JPs.


Observed effects

Windows XP Professional

Windows Explorer

  • Deleting a JP using explorer is not safe — it will delete the targeted files immediately as if using shift-delete.
  • Beware: if the JP is sent to the recycle bin, the targeted files will look safe, but will be deleted when the recycle bin is emptied.
  • Moving the JP to a different location on the same drive only moves the JP, however moving to another drive turns the JP into a normal folder and moves all files there (leaving the targeted directory empty).
  • Whilst walking through the directory with explorer, it seems impossible to delete folders, however files can be deleted.
  • A solution for these issues is installing NTFS Link, which makes Windows Explorer handle junctions correctly. One can also use the fsutil application to delete and query reparse points (administration privileges are required).

Windows Explorer running on Windows Vista Windows Explorer running on Windows XP Windows Explorer is an application that is part of modern versions of the Microsoft Windows operating system that provides a graphical user interface for accessing the file systems. ...

Console

On the cmd.exe command prompt:

  • The dir command in Windows 2000 or later recognizes junction points, displaying <JUNCTION> instead of <DIR> in directory listings.
  • Any commands that would normally affect files inside a normal directory will act the same here, so don't use del myjunction — this will just delete all the files in the targeted folder.
  • rmdir & move seem to work fine with junctions, with the caveat that move won't let you move the junction to another volume (as opposed to Windows Explorer, as mentioned above.)
  • rmdir seems safe in that it only deletes the JP, not the targeted files.
  • Whilst walking through the directory with the console, files can be deleted, but unlike explorer, directories can also be deleted (using rmdir/s dirname for example.)
  • Using the linkd command with the /d switch is a safe way to delete junction points.

Windows 2000 (also referred to as Win2K) is a preemptible, interruptible, graphical and business-oriented operating system that was designed to work with either uniprocessor or symmetric multi-processor 32-bit Intel x86 computers. ... Windows Explorer running on Windows Vista Windows Explorer running on Windows XP Windows Explorer is an application that is part of modern versions of the Microsoft Windows operating system that provides a graphical user interface for accessing the file systems. ...

General

  • Interesting tidbit: an infinite loop in the file structure can be created by placing a JP in the folder it targets. (Creating this is not recommended.)
  • ACL inheritance is by design based on volumes and not working across junctions.
  • Disk free space might not show up correctly. This depends on the API call the application is using. The old style GetDiskFreeSpace() function the Windows Explorer is using does only accept the root directory of a device and will therefore only show the amount of free space of the root volume. Reparse point-aware applications use GetDiskFreeSpaceEx() to determine the free disk space of the device of a specific directory.

An application programming interface (API) is a source code interface that a computer system or program library provides to support requests for services to be made of it by a Length. ... In computer file systems, the root directory is the first or top-most directory in a hierarchy. ...

Windows Vista

Windows Vista supports a new NTFS symbolic link capability that replaces junction points in Windows 2000 and Windows XP. Microsoft has implemented its symbolic links to function just like UNIX links. They are designed to aid in migration and application compatibility with UNIX operating systems. In computing, an NTFS symbolic link (symlink) is a file-system object that points to another file system object. ...


External links

Informative

  • Codeproject Article – discussion on the source code of a junction point utility, aimed at programmers
  • PC Mag Article about adding any folder to the start menu (so that you can view the contents as submenus).
  • Microsoft Knowledge Base Article – 'How to Create and Manipulate NTFS Junction Points'

Other

  • Junction Link Magic – Windows graphical interface for creating, updating and deleting junction points
  • Winbolic Link – Windows graphical interface for creating, updating and deleting junction points and shortcuts
  • NTFS-Link – Windows shell extension that allows creating junction points and hard links. Existing junction points and hardlinks get marked by a small additional icon in the explorer.
  • Junction – command line utility with source code
  • Hardlink Shell Extension – adds new entries for managing hardlinks and junctions into the Windows Explorer context menus
  • Link Creation Shell Extension – another windows shell extension that allows creating junction points and hard links.

  Results from FactBites:
 
How to create and manipulate NTFS junction points (606 words)
To delete the mydesktop junction point, at a command prompt, type linkd mydesktop /d or Delrp mydesktop.
Use NTFS ACLs to protect files and directories that are targeted by junction points from inadvertent deletion or other file system operations.
NTFS junction points are similar to the junction points in DFS because both are tools that are used to graft storage namespaces together.
  More results at FactBites »

 
 

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