Editing NTFS (section)

=== Hard links ===
The [[hard link]] feature allows different file names to directly refer to the same file contents. Hard links may link only to files in the same volume, because each volume has its own [[#Master File Table|MFT]].
Hard links were originally included to support the [[POSIX]] subsystem in Windows NT.<ref>{{cite web|title=Chapter 29 – POSIX Compatibility|url=https://learn.microsoft.com/en-us/previous-versions//cc768080(v=technet.10)|work=MS Windows NT Workstation 4.0 Resource Guide|publisher=[[Microsoft]]|access-date=25 January 2025|year=1995}}</ref>

Although hard links use the same MFT record ([[inode]]) which records file metadata such as file size, modification date, and attributes, NTFS also caches this data in the directory entry as a performance enhancement. This means that when listing the contents of a directory using FindFirstFile/FindNextFile family of APIs, (equivalent to the POSIX opendir/readdir APIs) you will also receive this cached information, in addition to the name and inode. However, you may not see up-to-date information, as this information is only guaranteed to be updated when a file is closed, and then only for the directory from which the file was opened.<ref>{{cite web|title=Hard Links and Junctions|url=https://learn.microsoft.com/en-us/windows/win32/fileio/hard-links-and-junctions|website=[[Microsoft Learn]]|publisher=[[Microsoft]]|access-date=25 January 2025|date=21 June 2024}}</ref> This means where a file has multiple names via hard links, updating a file via one name does not update the cached data associated with the other name. You can always obtain up-to-date data using GetFileInformationByHandle (which is the true equivalent of POSIX stat function). This can be done using a handle which has no access to the file itself (passing zero to CreateFile for dwDesiredAccess), and closing this handle has the incidental effect of updating the cached information.

Windows uses hard links to support [[8.3 filename|short (8.3) filenames]] in NTFS. Operating system support is needed because there are legacy applications that can work only with 8.3 filenames, but support can be disabled. In this case, an additional filename record and directory entry is added, but both 8.3 and long file name are linked and updated together, unlike a regular hard link.

The NTFS file system has a limit of 1023 [[hard link]]s on a file.<ref>{{cite web |title=CreateHardLinkA function (winbase.h) |date=June 2023 |url=https://learn.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-createhardlinka|access-date=25 January 2025}}</ref>{{clarify|is this a limitation of the NTFS on-disk data structure or of Windows NT for all file systems that support hard links?|date=December 2024}}