The NTFS file system provides the ability to create a system representation of a file or directory in a location in the directory structure that is different from the file or directory object that is being linked to. This process is called linking.There are three types of file links supported in the NTFS file system: hard links, junctions, and symbolic links.
A symbolic link is a file-system object that points to another file system object. The object being pointed to is called the target.
Symbolic links are transparent to users; the links appear as normal files or directories, and can be acted upon by the user or application in exactly the same manner.
Symbolic links are designed to aid in migration and application compatibility with UNIX operating systems. Microsoft has implemented its symbolic links to function just like UNIX link.
Symbolic links can point to non existent targets because the operating system does not check to see if the target exists.
Hard Links and Junctions
There are three types of file links supported in the NTFS file system: hard links, junctions, and symbolic links. This topic is an overview of hard links and junctions. For information about symbolic links, see Creating Symbolic Links.
A hard link is the file system representation of a file by which more than one path references a single file in the same volume. To create a hard link, use the CreateHardLink function. Any changes to that file are instantly visible to applications that access it through the hard links that reference it. However, the directory entry size and attribute information is updated only for the link through which the change was made. Note that the attributes on the file are reflected in every hard link to that file, and changes to that file's attributes propagate to all the hard links. For example if you reset the READONLY attribute on a hard link to delete that particular hard link, and there are multiple hard links to the actual file, then you will need to reset the READONLY bit on the file from one of the remaining hard links to bring the file and all remaining hard links back to the READONLY state.
For example, in a system where C: and D: are local drives and Z: is a network drive mapped to \\fred\share, the following references are permitted as a hard link:
- C:\dira\ethel.txt linked to C:\dirb\dirc\lucy.txt
- D:\dir1\tinker.txt to D:\dir2\dirx\bell.txt
- C:\diry\bob.bak linked to C:\dir2\mina.txt
The following are not:
- C:\dira linked to C:\dirb
- C:\dira\ethel.txt linked to D:\dirb\lucy.txt
- C:\dira\ethel.txt linked to Z:\dirb\lucy.txt
To delete a hard link, use the DeleteFile function. You can delete hard links in any order regardless of the order in which they are created.
A junction (also called a soft link) differs from a hard link in that the storage objects it references are separate directories, and a junction can link directories located on different local volumes on the same computer. Otherwise, junctions operate identically to hard links. Junctions are implemented through reparse points.
Assuming the same conditions in the Hard Links section, the following references are permitted as junctions:
- C:\dira linked to C:\dirb\dirc
- C:\dirx linked to D:\diry
The following are not:
- C:\dira\one.txt linked to C:\dirb\two.txt
- C:\dir1 linked to Z:\dir2