Undeletion

Undeletion is a feature for restoring s which have been removed from a by . 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. Undeletion can both help prevent users from accidentally losing data, or can pose a computer security risk, since users may not be aware that deleted files remain accessible. Not all file systems or operating systems support undeletion. Undeletion is possible on all file systems, with undeletion utilities provided since MS-DOS 5.0 and DR DOS 6.0 in 1991. 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 utilities like ext4magic, extundelete, PhotoRec and ext3grep were written to automate the undeletion on ext3 volumes. Undelete was proposed in ext4, but is yet to be implemented. 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. List of DOS commands Norton UNERASE was an important component in Norton Utilities version 1.0 in 1982. Microsoft included a similar UNDELETE program in versions 5.0 to 6.22 of MS-DOS, but applied the Recycle Bin approach instead in later operating systems using FAT. DR DOS 6.0 and higher support UNDELETE as well, but optionally offer additional protection utilizing the FAT snapshot utility DISKMAP and the resident DELWATCH deletion tracking component, which actively maintains deleted files' date and time stamps and keeps the contents of deleted files from being overwritten unless running out of disk space. DELWATCH also supports undeletion of remote files on file servers. Since Novell DOS 7 the kernel will store the first letter of deleted files in the directory entries in order to further assist undeletion tools in recovering the original name.