File deletion
Encyclopedia
File deletion is a way of removing a file
from a computer's file system
.
The reasons for deleting files are
All operating systems include commands for deleting files (rm
on Unix
, delete/del in MS-DOS
, Microsoft Windows
etc.). File manager
s also provide a convenient way of deleting files. Files may be deleted one-by-one, or a whole directory tree may be deleted.
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 Mac OS X
both 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. Defrag
ging 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 read-only
. Many operating system
s 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.
s only remove the link to data (see undelete
, above). But even overwriting parts of the disk with something else or formatting it may not guarantee that the sensitive data is completely unrecoverable. Special software is available that overwrites data, and modern (post-2001) ATA drives include a secure erase command in firmware. However high security applications sometimes require that a disk drive be physically destroyed to ensure data is not recoverable, as microscopic changes in head alignment and other effects can mean even such measures are not guaranteed.
Computer file
A computer file is a block of arbitrary information, or resource for storing information, which is available to a computer program and is usually based on some kind of durable storage. A file is durable in the sense that it remains available for programs to use after the current program has finished...
from a computer's file system
File system
A file system is a means to organize data expected to be retained after a program terminates by providing procedures to store, retrieve and update data, as well as manage the available space on the device which contain it. A file system organizes data in an efficient manner and is tuned to the...
.
The reasons for deleting files are
- Freeing the disk space
- Removing duplicate or unnecessary data to avoid confusion
- Making sensitive informationInformation sensitivityInformation sensitivity is the control of access to information or knowledge that might result in loss of an advantage or level of security if disclosed to others who might have low or unknown trustability or undesirable intentions....
unavailable to others
All operating systems include commands for deleting files (rm
Rm (Unix)
rm is a basic UNIX command used to remove objects such as files, directories, device nodes, symbolic links, and so on from the filesystem...
on Unix
Unix
Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...
, delete/del in MS-DOS
MS-DOS
MS-DOS is an operating system for x86-based personal computers. It was the most commonly used member of the DOS family of operating systems, and was the main operating system for IBM PC compatible personal computers during the 1980s to the mid 1990s, until it was gradually superseded by operating...
, Microsoft Windows
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
etc.). File manager
File manager
A file manager or file browser is a computer program that provides a user interface to work with file systems. The most common operations performed on files or groups of files are: create, open, edit, view, print, play, rename, move, copy, delete, search/find, and modify file attributes, properties...
s also provide a convenient way of deleting files. Files may be deleted one-by-one, or a whole directory tree may be deleted.
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 back upBackup
In information technology, a backup or the process of backing up is making copies of data which may be used to restore the original after a data loss event. The verb form is back up in two words, whereas the noun is backup....
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
Temporary folder
In computing, a temporary folder or temporary directory is a directory used to hold temporary files. Many operating systems and some software automatically delete the contents of this directory at bootup or at regular intervals....
whose contents can then be deleted at will. This is how the "recycle bin
Recycle bin (computing)
In computing, the trash is temporary storage for files that have been deleted in a file manager by the user, but not yet permanently erased from the physical media...
" or "trash can" works. Microsoft Windows
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
and Apple's Mac OS X
Mac OS X
Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...
both employ this strategy.
In MS-DOS
MS-DOS
MS-DOS is an operating system for x86-based personal computers. It was the most commonly used member of the DOS family of operating systems, and was the main operating system for IBM PC compatible personal computers during the 1980s to the mid 1990s, until it was gradually superseded by operating...
, one can use the undelete
Undeletion
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...
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. Defrag
DeFRaG
DeFRaG is a free software modification for id Software's first-person shooter computer game Quake III Arena . The mod is dedicated to player movements and trickjumping.Trickjumping is an integral part of the game allowing a player to jump higher, farther and move faster...
ging 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 read-only
Read-only
In computing, read-only can mean:* Read-only memory , a type of storage media* Read-only access to files or directories in file system permissions...
. Many operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
s will warn the user trying to delete such files. Where file system permissions
File system permissions
Most current file systems have methods of administering permissions or access rights to specific users and groups of users. These systems control the ability of the users to view or make changes to the contents of the filesystem....
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.
Problem with sensitive data
The common problem with sensitive data is that deleted files are not really erased and so may be recovered by interested parties. Most file systemFile system
A file system is a means to organize data expected to be retained after a program terminates by providing procedures to store, retrieve and update data, as well as manage the available space on the device which contain it. A file system organizes data in an efficient manner and is tuned to the...
s only remove the link to data (see undelete
Undeletion
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...
, above). But even overwriting parts of the disk with something else or formatting it may not guarantee that the sensitive data is completely unrecoverable. Special software is available that overwrites data, and modern (post-2001) ATA drives include a secure erase command in firmware. However high security applications sometimes require that a disk drive be physically destroyed to ensure data is not recoverable, as microscopic changes in head alignment and other effects can mean even such measures are not guaranteed.
See also
- Data erasureData erasureData erasure is a software-based method of overwriting data that completely destroys all electronic data residing on a hard disk drive or other digital media. Permanent data erasure goes beyond basic file deletion commands, which only remove direct pointers to data disk sectors and make data...
- Data remanenceData remanenceData remanence is the residual representation of data that remains even after attempts have been made to remove or erase the data. This residue may result from data being left intact by a nominal file deletion operation, by reformatting of storage media that does not remove data previously written...
- UndeletionUndeletionUndeletion 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...