File deletion
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File deletion is a way of removing a file from a computer's file system.
The reasons for deleting files are
- Freeing the disk space
- Removing duplicate or unnecessary data to avoid confusion
- Making sensitive information unavailable to others
All operating systems include commands for deleting files (rm on Unix, delete/del in MS-DOS etc.). File managers also provide a convenient way of deleting files. Files may be deleted one-by-one, or a whole directory tree may be deleted.
[edit] Problem with accidental removal
The common problem with deleting files is accidental removal of information that later proves to be important. One way to deal with this is to backup files regularly. Erroneously deleted files may then be found in archives.
Another strategy is not to delete files instantly, but to move them to a temporary directory whose contents can then be deleted at will. This is how the "recycle bin" (also known as "trash folder") works.
In MS-DOS, one can use the undelete command. In MS-DOS the deleted files are not really deleted, but only marked as deleted — so they could be undeleted during some time, until the disk blocks they used are eventually taken up by other files. Defragging a drive will prevent undeletion, as the blocks used by deleted file will be overwritten since they are marked as "empty".
Another precautionary measure is to mark important files as read-only. Many operating systems will warn the user trying to delete such files. Where file system permissions exist, "ordinary" users are only able to delete their own files, preventing the erasure of other people's work or critical system files.
Under Unix-like operating systems, in order to delete a file, one must usually have write permission to the parent directory of that file.
[edit] Problem with sensitive data
The common problem with sensitive data is that deleted files are not really deleted and so may be recovered by interested parties. Most file systems only remove the link to data (see undelete above). But even overwriting the disk with something else or formatting it does not guarantee that the sensitive data is completely unrecoverable.
