Mac OS X: Apple Double Format Creates File Name With the Prefix '._'

  • Last Modified: September 18, 2003
  • Article: TA20578
  • Old Article: 106510
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In some cases involving the Apple Double format, moving a file to a different file system will cause the prefix "._" to appear on a file name.

Products Affected

Mac OS X 10.2, Mac OS X 10.0

Symptom

The prefix "._" appears on a file name.


Solution

Before Mac OS X, the Mac OS used 'forked' files, which have two components: a data fork and a resource fork. The Mac OS Standard (HFS) and Mac OS Extended (HFS Plus) disk formats support forked files. When you move these types of files to other disk formats, the resource fork can be lost.

With Mac OS X, there is a mechanism called "Apple Double" that allows the system to work with disk formats that do not have a forked file feature, such as remote NFS, SMB, WebDAV directories, or local UFS volumes. Apple Double does this by converting the file into two separate files. The first new file keeps the original name and contains the data fork of the original file. The second new file has the name of the original file prefixed by a "._ " and contains the resource fork of the original file. If you see both files, the ._ file can be safely ignored. Sometimes when deleting a file, the ._ component will not be deleted. If this occurs you can safely delete the ._ file.
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