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Undeletion is a feature for restoring computer files which have been removed from a file system by file deletion. Deleted data can be recovered on many file systems, but not all file systems provide an undeletion feature. Recovering data without an undeletion facility is usually called data recovery, rather than undeletion. Although undeletion can help prevent users from accidentally losing data, it can also pose a computer security risk, since users may not be aware that deleted files remain accessible. ==Support== Not all file systems or operating systems support undeletion. Undeletion is possible on FAT16 file systems, with Microsoft providing undeletion utilities for both MS-DOS 5-6.22 and 16-bit Windows operating systems. It is not supported by most modern UNIX file systems, though AdvFS is a notable exception. The ext2 file system has an add-on program called (e2undel ) which allows file undeletion. The similar ext3 file system does not officially support undeletion, but ext3grep was written to automate the undeletion of ext3 volumes. Undelete was proposed in ext4, but is yet to be implemented.〔(New ext4 features )〕 However, a trash bin feature was posted as a patch on December 4, 2006. The Trash bin feature uses undelete attributes in ext2/3/4 and Reiser file systems. Graphical user environments often take a different approach to undeletion, instead using a "holding area" for files to be deleted. Undesired files are moved to this holding area, and all of the files in the holding area are deleted periodically or when a user requests it. This approach is used by the ''Trash can'' in Macintosh operating systems and by the recycle bin in Microsoft Windows. This is a natural continuation of the approach taken by earlier systems, such as the limbo group used by LocoScript. This approach is not subject to the risk that other files being written to the filesystem will disrupt a deleted file very quickly; permanent deletion will happen on a predictable schedule or with manual intervention only. Another approach is offered by programs such as ''Norton GoBack'' (formerly ''Roxio GoBack''): a portion of the hard disk space is set aside for file modification operations to be recorded in such a way that they may later be undone. This process is usually much safer in aiding recovery of deleted files than the undeletion operation as described below. Similarly, file systems that support "snapshots" (like ZFS or btrfs), can be used to make snapshots of the whole file system at regular intervals (e.g. every hour), thus allowing recovery of files from an earlier snapshot. 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「Undeletion」の詳細全文を読む スポンサード リンク
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