File deletion

File deletion is the removal of a from a computer's . All operating systems include commands for deleting files (rm on Unix, era in CP/M and DR-DOS, del/erase in MS-DOS/PC DOS, DR-DOS, Microsoft Windows etc.). s also provide a convenient way of deleting files. Files may be deleted one-by-one, or a whole blacklist directory tree may be deleted. Examples of reasons for deleting files are: Freeing the disk space Removing duplicate or unnecessary data to avoid confusion Making sensitive information unavailable to others Removing an operating system or blanking a hard drive Data recovery A common problem with deleting files is the accidental removal of information that later proves to be important. A common method to prevent this is to back up files regularly. Erroneously deleted files may then be found in archives. Another technique often used 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" or "trash can" works. Microsoft Windows and Apple's macOS, as well as some Linux distributions, all employ this strategy. 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. This is how data recovery programs work, by scanning for files that have been marked as deleted. As the space is freed up per byte, rather than per file, this can sometimes cause data to be recovered incompletely. Defragging a drive may prevent undeletion, as the blocks used by deleted file might be overwritten since they are marked as "empty". Another precautionary measure is to mark important files as . Many operating systems will warn the user trying to delete such files. Where exist, users who lack the necessary permissions are only able to delete their own files, preventing the erasure of other people's work or critical system files.