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In computing, a hard link is a directory entry that associates a name with a file on a file system. (A directory is itself a special kind of file, that contains a list of such entries.) The term is used in file systems which allow multiple hard links to be created for the same file. This has the effect of creating multiple names (e.g. names with path, as identical file names for the same file can be created in distinct directories) for the same file, causing an aliasing effect: e.g. if the file is opened by one of its names, and changes are made to its content, then these changes will also be visible when the file is opened by an alternative name. By contrast, a soft link on such file systems is not a link to a file itself, but to a file name. This also creates aliasing, but in a different way. Directories are files, so multiple hard links to directories are possible; However, their unrestricted creation is usually avoided, because of the cyclic structures this may create. Hard links—that is, multiple directory entries to the same file—are supported by POSIX-compliant and partially POSIX-compliant operating systems, such as Linux, Android, Mac OS X, Windows NT4 and later Windows NT operating systems. Support also depends on the type of file system being used. For instance, the NTFS file system supports hard links, while FAT and ReFS do not. ==Usage== On POSIX-compliant and partially POSIX-compliant operating systems, such as all Unix-like systems, additional hard links to existing files are created with the system call, or the ln and link command-line utilities. The stat command can reveal how many hard links point to a given file. The link count is also included in the output of ls -l.On Microsoft Windows, hard links can be created using the mklink /H command on Windows NT 6.0 and later systems (such as Windows Vista), and in earlier systems (Windows XP, Windows Server 2003) using fsutil.exe hardlink create.The Windows API from Windows 2000 onwards includes a CreateHardLink() call to create hard links, DeleteFile() is used to remove them, and GetFileInformationByHandle() can be used to determine the number of hard links associated with a file.〔(【引用サイトリンク】title=NTFS Hard Links, Directory Junctions, and Windows Shortcuts )〕 Hard links require an NTFS partition. Starting with Windows Vista, hard links are used by Windows Component Store (WinSxS) to keep track of different versions of DLLs stored on the hard disk drive. Unix-like emulation or compatibility software running on Windows, such as Cygwin and Subsystem for UNIX-based Applications, allow the use of POSIX interfaces under Windows. The process of ''unlinking'' dissociates a name from the data on the volume without destroying the associated data. The data is still accessible, as long as at least one link that points to it still exists. When the last link is removed, the space is considered free. A process ambiguously called undeleting allows the recreation of links to data that are no longer associated with a name. However, this process is not available on all systems and is often not reliable. When a file is deleted, it is added to a free space map for re-use. If a portion of the deleted file space is claimed by new data, undeletion will be unsuccessful, because some or all of the previous data will have been overwritten, and may result in cross-linking with the new data and leading to filesystem corruption. Additionally, deleted files on solid state drives may be erased at any time by the storage device for reclamation as free space. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Hard link」の詳細全文を読む スポンサード リンク
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