MAC Times - Change Time and Creation Time (ctime)

Change Time and Creation Time (ctime)

Unix and Windows file systems interpret 'ctime' differently:

  • Unix systems maintain the historical interpretation of ctime as being the time when certain file metadata, not its contents, were last changed, such as the file's permissions or owner (e.g. 'This file's metadata was changed on 05/05/02 12:15pm').
  • Windows systems use ctime to mean 'creation time' (also called 'birth time') (e.g. 'This file was created on 05/05/02 12:15pm').

This difference in usage can lead to incorrect presentation of time metadata when a file created on a Windows system is accessed on a Unix system and vice versa. Most Unix file systems don't store the creation time, although some, such as HFS+, ZFS, and UFS2 do. NTFS stores both the creation time and the change time.

The semantics of creation times is the source of some controversy. One view is that creation times should refer to the actual content of a file: e.g. for a digital photo the creation time would note when the photo was taken or first stored on a computer. A different approach is for creation times to stand for when the file system object itself was created, e.g. when the photo file was last restored from a backup or moved from one disk to another.

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