Control-Alt-Delete (often abbreviated to Ctrl-Alt-Del, also known as the "three-finger salute") is a computer keyboard command on IBM PC compatible systems that can be used to reboot the computer, and summon the task manager or Windows Security in more recent versions of the Microsoft Windows operating system. It is invoked by pressing the Delete key while holding the Control and Alt keys: Ctrl+Alt+Delete. It forces a soft reboot, brings up the task manager (on Windows and BeOS) or a jump to ROM monitor. In most X desktops, it brings up the Logout dialog. These keys are sometimes referred to in computer manuals as interrupt keys, since they are often used to interrupt the operation of a malfunctioning program.
- 1 History
- 2 MS-DOS and other real mode systems
- 3 Windows
- 4 OS/2
- 5 Linux
- 6 Mac
- 7 Apple II and Apple III
- 8 Equivalents on various platforms
- 9 See also
- 10 In popular culture
- 11 References
- 12 External links
This keyboard combination was invented by David Bradley, a designer of the original IBM PC. Bradley originally designed Control-Alt-Escape to trigger a soft reboot (without warning or confirmation by the user), but he found it was too easy to bump the left side of the keyboard and reboot the computer accidentally. He switched the key combination to Control-Alt-Delete, a combination that was impossible to press with just one hand (this is not true of later keyboards, such as the 102-key PC/AT keyboard or the Maltron keyboard). More advanced operating systems use its status as a "reserved" combination for various purposes, but often retain the ability to trigger a soft reboot in certain configurations or circumstances. Bradley is also known for his good-natured jab at Bill Gates, at that time the CEO of Microsoft, and also the creator of many of Microsoft's programs: "I may have invented Control-Alt-Delete, but Bill Gates made it famous". He afterwards elaborated that it was made more famous due to Windows NT logon procedures ("Press Ctrl + Alt + Delete to log on"). However, while Bradley implemented the key sequence in the ROM BIOS, he did not suggest it; the team of the then chief programmer of the IBM PC Project, Mel Hallerman, did.
MS-DOS and other real mode systems
On a PC running DOS or a system that runs in real mode, this keystroke combination is recognized by the keyboard handling code in the BIOS unless the keyboard interrupt has been hooked by some other resident program. The BIOS reacts by invoking a soft (aka warm) reboot. Under Windows 3.0 and earlier (and Windows 3.1x running in Standard mode), Control-Alt-Delete reboots the computer as in MS-DOS.
In Windows 3.1x running in 386 Enhanced mode, Windows 95, Windows 98, and Windows Me, this keystroke combination is recognised by the Windows keyboard device driver. According to the value of the LocalReboot option in the [386Enh] section of system.ini, Windows performs one of several actions in response:
- If LocalReboot=Off it performs a soft reboot.
- If LocalReboot=On:
- Windows 3.1x presents a blue screen to the user inviting them to press Enter to end a task that has stopped responding to the system (if such a task exists) or press Control-Alt-Delete again to perform a soft reboot.
- Windows 95, Windows 98, and Windows Me, temporarily halts the entire system, and presents a window which lists currently running processes, and can be used to notify them that they should end, or, when they don't respond, kill them. The user can press Control-Alt-Delete again to perform a soft reboot.
Killing tasks/processes is useful, for instance, if a program has entered an infinite loop. Theoretically, the system's other processes should continue normally—in practice, using this key combination to terminate a program/process in Windows 3.1 can result in resources and memory being leaked. As such, it is strongly recommended that, following a process kill in these versions of Windows, any work should be saved in any other applications and Windows should be restarted. Such damage is much less likely in newer versions of DOS-based Windows because of resource tracking.
In Windows 9x, pressing the combination a second time if the process listing has not appeared will display a blue screen from which the user can reboot the system by pressing the combination a third time; other times the system restarts on the second Ctrl-Alt-Delete combination. This allows the user to over-ride any "stuck" process, since no user-level program is able to define its own response to the Control-Alt-Delete key combination. However, this functionality does not always work.
Windows NT (and later versions)
In Windows NT, and thus on its successors, including Windows 2000, Windows XP, Windows Server 2003, Windows Vista, Windows Server 2008 and Windows 7, this keystroke combination is recognized (as a special system-wide "keyboard hook") by the Winlogon process, which in response instructs GINA to perform one of the following tasks:
- If nobody is logged in, bringing up the login dialog to allow the user to log in. Also used when the computer is locked to bring up the unlock dialog.
- If the computer is configured as a part of a domain or it runs Windows 2000, the combination brings up the "Windows Security" dialog, where the user can lock the computer, change their password, log out, shut the computer down, or invoke the Task Manager. This is the default behavior in Windows Vista and Windows Server 2008, regardless of whether or not the computer is part of a domain. The options presented can be controlled through the use of Group Policy.
- If Windows XP is not connected to a domain
- and the Welcome Screen and fast user switching are turned on, Ctrl-Alt-Del directly invokes the Task Manager.
- and the Welcome Screen and fast user switching are turned off, Ctrl-Alt-Del will open the Windows Security Dialog, as described above.
- If pressed twice while at the Welcome Screen the classic Windows login box is displayed. This allows one to log in as any user, even those typically hidden from the Welcome Screen.
Windows NT is designed so that, unless system security is already compromised in some other way, only the Winlogon process, a trusted system process, can receive notification of this keystroke combination. This is because the kernel remembers the process ID of the Winlogon process, and allows only that process to receive the notification. This keystroke combination is thus called the Secure Attention Sequence. A user pressing Control-Alt-Delete can be sure that it is the operating system (specifically the Winlogon process), rather than a third party program that is responding to the key combination (see Login spoofing), and that it is therefore safe to enter a password. It was chosen as the secure attention key in Windows (instead of, for example, the System Request key), because on the PC platform no program could reasonably expect to redefine this keystroke combination for its own purposes (this is the soft reboot combination in BIOS and DOS).
It is also a reliable method for bringing up the Task Manager in Windows 2000 and older. All other keystroke combinations could potentially be exclusively tied up by a process that is stuck, but a user process is not able to intercept the Control-Alt-Delete sequence. Ctrl+Shift+Esc also brings up the task manager in all Windows NT versions starting with NT 4.0, even if pressing Ctrl+Alt+Del is set to bring up the Windows Security dialog. The task manager can be however disabled by Windows Group Policies.
As a side effect, users who do not have physical access to the computer's power supply and power/reset switches can be denied the ability to shut down or restart the computer, where previously (on MS-DOS and other variants of Windows) they could always use Control-Alt-Delete. However, as both the Task Manager and Windows Security have options for shutting down the computer, this operation can still be executed unless the entire system (including the Winlogon process) is unresponsive. Also, it is sometimes impossible to access and/or see the Task Manager after a full-screen application has frozen, although the Windows Security dialog, which is on a separate "secure desktop", almost always appears.
Windows Vista and later
In Windows Vista and other NT operating systems based on it (such as Windows Server 2008 and Windows 7), most Ctrl+Alt+Del actions remain the same. There is no supported method of replacing the login interface (as there was in Windows XP), but there is a flexible system for modifying it. The classic logon screen has been completely removed, replaced with an updated welcome screen, similar to that from Windows XP. As in Windows XP, the welcome screen can be configured to require the user to press Ctrl+Alt+Del before logon. In Windows XP, this is done by configuring local security policy. While the default behavior is to have icons for each user, the welcome screen can be configured to prompt for a username and password, though it retains the new UI. Additionally, pressing Ctrl+Alt+Del when logged in always brings up the Windows Security screen, regardless of the logon method. Users can also lock the computer even if fast user switching is enabled.
In OS/2, this keystroke combination is recognised by the OS/2 keyboard device driver, which notifies the session manager process. The normal session manager process in OS/2 versions 2.0 and later is the parent Workplace Shell process, which displays the "The system is rebooting" window and triggers a soft reboot. If it is pressed twice in succession OS/2 triggers an immediate soft reboot, without waiting for the session manager process.
In both cases, the system flushes the page cache, cleanly unmounts all disc volumes, but does not cleanly shut down any running programs (and thus does not save any unsaved documents, or the current arrangements of the objects on the Workplace Shell desktop or in any of its open folders).
In Linux, this keystroke combination is recognized by the keyboard device driver in the kernel. In the absence of more specific instructions, which will usually only be during system initialization, the kernel directly initiates a soft reboot in response. More commonly, the kernel will send a signal to the init process, which will perform an administrator-configured task, such as running a script, or displaying an "end current session" box in KDE.
In many Linux distributions, init is configured to switch run levels and to perform a soft reboot in response to the signal. Thus it provides a mechanism for a person with physical access to the keyboard to perform system shut down (a task that requires superuser rights to initiate programmatically). However, Linux systems can be configured to ignore the keystroke combination. The setting is usually in the inittab(5) configuration file under the keyword "ca".
Linux also has a similar sequence of keystrokes for restarting the computer described at the article Magic SysRq key.
Under the X Window System (the graphics display and windowing framework upon which most Linux and BSD GUIs are based), Control-Alt-Backspace kills the X server—normally killing all programs using it (including the window manager)—but not the underlying operating system. When a display manager is used, it restarts the killed X server.
Ctrl-Alt-Delete is not specified as a keyboard shortcut for anything on the Mac and various other platforms. However, in the Mac OS X Server logon screen, pressing Control-Option-Delete will show an alert saying "This is not DOS." 
- Control-⇧ Shift–⏏ Media Eject
- ⌘ Cmd-Option–⏏ Media Eject
Quit all applications and restart:
- ⌘ Cmd-Control–⏏ Media Eject
Restart, Sleep or Shut Down (dialogue):
In an emergency — or if normal actions are impossible/ineffective — as a last resort, you may force things. Be aware that forcing things to quit, restart or stop may have undesirable effects such as data loss.
Force Quit Applications
For windowed processes/applications, to present the Force Quit Applications dialogue:
- ⌘ Cmd-Option-Escape
- or use the Force Quit… command in the Apple menu.
Activity Monitor utility can quit, or force quit, any process.
Force the computer to restart
- ⌘ Cmd-Control-Power
Some Macs have a ◁ Reset button.
Force the computer to shut down
- press the Power button for five seconds or more.
Apple II and Apple III
Equivalents on various platforms
Platform Key combination Function Acorn Machines (pre-1987) Break Processor reset, although confusingly always referred to as soft reset. Hold down Ctrl as well for so-called hard reset (reinitializes various settings); hold down Shift to boot from disk (or not to, if disk is the default). Acorn and post-Acorn RISC OS machines. Reset button Processor reset, although confusingly always referred to as soft reset. Hold down Ctrl as well for so-called hard reset (reinitializes various settings); hold down Shift to boot from disk (or not to, if disk is the default). Hold down various other keys to restore CMOS settings to safe configurations. Ctrl + Break Perform a soft reboot. Amiga Ctrl + Left Amiga (or Commodore) + Right Amiga Hard reset. The reset will be instant unless a specific hardware delay function has been activated. Amstrad CPC 464 and CPC6128 Ctrl + Shift + Esc Reset (cold) Amstrad PCW Shift + Extra + Exit Reset (cold) Shift + Extra + Relay Warm boot from the currently-inserted floppy disc. Is able to boot from discs in LocoScript installer format, which cannot be loaded by the normal ROM loader. Atari ST Ctrl + Alt + Del Soft reset. Under FreeMiNT >= 1.16 it won't be instant, disk partitions are unmounted first. Ctrl + Alt + Shift + Del will perform hard reset. IBM PC under DOS Ctrl + Alt + Del Perform a soft reboot IBM PC under Windows 3.x shell Ctrl + Alt + Del Close unresponsive applications or (if pressed twice) perform a soft reboot IBM PC under Microsoft Windows (95, 98, and Me) Ctrl + Alt + Del Bring up simplistic task manager (actually "Close Program" dialog) or (if pressed twice) perform a soft reboot IBM PC under Windows NT-based OS (NT, 2000, XP, 2003, Vista and Windows 7) Ctrl + Shift + Esc Bring up the Windows Task Manager Ctrl + Alt + Del Also known as the Secure Attention Sequence; bring up the logins screen (when pressed in login screen), or the "Windows security" dialog or (configurable on Windows 2000 and later) the Windows Task Manager (when logged in) IBM PC under OS/2 Ctrl + Esc Bring up the Window List (unblocking the synchronous input queue) Ctrl + Alt + Del Perform a soft reboot Ctrl + Alt + NumLock (twice) Halt the system and begin a system dump to floppy disk IBM PC under Linux Ctrl + Alt + Del Signal the init process (usually configured to soft reboot) Alt + SysRq + function key Magic SysRq key: Depending on the function key, performs a certain low-level function. Examples: sync (flush caches), reboot (forced soft reboot), unmount (remount filesystems readonly), etc... IBM PC under other OS Ctrl + Alt + Del Often (but not always) configured to reboot Sinclair ZX Spectrum Break Halted peripheral (cassette tape or printer) operations with the report D BREAK – CONT repeats, or halted BASIC programs with the report L BREAK into program. Sun workstation L1/Stop + A Enter ROM monitor Sun workstation (serial console) Break Enter ROM monitor Alphas running OpenVMS Ctrl + P Enter ROM Serial Console or reboot, depending on setting in SRM Apple II series machines Ctrl + Reset Enter the monitor or ROM BASIC Ctrl + Open Apple + Reset Reboot the machine Ctrl + Option (Closed Apple) + Reset Enter BIOS setup, then reboot Ctrl + Option (Closed Apple) + Open Apple + Reset Self-test, then reboot Ctrl + Open Apple + Escape Kill application Apple Macintosh computers with power button on keyboard Command + Power Enter debugger Control + Command + Power (sometimes known as a "Control Flower Power") Reboot the machine Mac OS (7 and later) Option + Command + Esc Force quit applications S60 Platform (used on some mobile phones such as Nokia smartphones) Green (call answer) + * + 3 (while restarting the phone) Wipes internal memory and resets the device SGI workstation Left Shift + Left Ctrl + Left Alt + Keypad Divide + F12 Restart X server (same as Ctrl + Alt + Backspace below). Nicknamed "the death-grip" due to the contorted finger positions. Commodore 64 & Vic-20 Run/Stop + Restore Halt (soft reconfiguration) and return to READY prompt Commodore 128 Reset Reset to power on state in current mode Commodore + Reset Reset to C-64 mode Run/Stop + Reset Reset to ML monitor preserving contents of BASIC memory X Window System Ctrl + Alt + Backspace Immediately kills the X server (the key can be disabled). When using an X Display Manager, it will usually start the X server again. TI-30XIIS On + Clear Restarts the calculator and clears RAM TI-80, TI-81, TI-82, TI-83, TI-84 Mode, Alpha, S Shows ROM version number. [Enter] enters self test mode TI-85, TI-86 2nd, Mode, Alpha, S Shows ROM version number. [Enter] enters self test mode TI-89 2nd + Left Arrow + Right Arrow + On Restarts the calculator and clears RAM
Esc + On Force Break without restarting RAM
Many Natural Display Casio Calculators Shift + 7 + On Restarts the calculator and clears RAM and EEPROM.
Continue pressing Shift to advance through self-test mode.
TI-99/4A FCTN-+ Resets machine back to startup screen. Voyage 200 2nd + Hand + On Restarts the calculator and clears RAM HP-48 On + C Restarts RPL, clearing the Stack and PICT, closing IO, and returning to the HOME directory (but not purging the memory) On + A + F As above, but also purges the memory BeOS Ctrl-Alt-Shift and click an applications entry in the Deskbar Kills application Zenith IBM PC clones Ctrl-Alt-Ins Brings up hardware configuration menu Scientific Atlanta Explorer DHCT Volume Down + Volume Up + Info (on settop box; not remote) Reboots box (starts up to blue EXPLORER screen) Olivetti M20 Ctrl + Reset Soft resets the machine TI Explorer Lisp Machine Left-Ctrl Left-Meta Right-Ctrl Right-Meta Abort Restart the system Xfce Ctrl + Alt + Esc + click on window Kill application Foxtel Set-top-boxes Back + Select (on box; not remote) (except UEC 720). Standby + Foxtel (on box; not remote) (UEC 720). Back + Select + Reset (on box; not remote) (iQ2) Power cycles the machine. Pressing [Power], Up, Down, [Power] when lights illuminate on box forces firmware update. iPod nano 3rd Generation Play/Pause + Center button (hold down until Apple logo shows) Reboots the iPod to the Apple logo that you see when you turn the iPod on for the first time. iPod nano 4th Generation Menu + Center button (hold down until Apple logo shows) Reboots the iPod to the Apple logo that you see when you turn the iPod on for the first time. iPod Touch, iPhone, and iPad Top Power Button + Center Home Button (hold down until Apple logo shows) Reboots the iPod, iPhone, or iPad to the Apple logo that you see when you turn the device on for the first time. Android devices, particularly the Nexus One Track ball + volume down + power, all held down until power off reboot normally if all buttons are released; reboot into bootloader if the volume down button is continuously held (from power off) volume down (held continuously) + Power button Enter the bootloader Alt + Shift + Del (on the device's hardware keyboard, if available) Reboots the device, particularly the Motorola Droid and its successor
- Winlogon — The Windows process that detects and responds to Ctrl+Alt+Del
- Secure attention key
- David Bradley, inventor of the Control-Alt-Delete combination for the original IBM PC.
- Parts of this article were originally based on the FOLDOC article Three-finger salute[dead link] at FOLDOC[dead link], used with permission.
In popular culture
The keystrokes are well known and infamous for escaping from problems in pop culture. For example, in the Billy Talent song "Perfect World", part of the lyrics include the sequence and associate it with resetting their memory and escaping from a situation: "Control-Alt-Deleted. Reset my memory." They were also used in a line in the "Weird Al" Yankovic Song - It's all about the Pentiums. "Play me online and you know that I'll beat you. If I ever meet you, I'll Control, alt, delete you" 
- ^ a b Crowley, Matthew (30 September 2001). "COMPUTING: BIG BLUE PERIOD". Las Vegas Review-Journal. http://www.reviewjournal.com/cgi-bin/printable.cgi?/lvrj_home/2001/Sep-03-Mon-2001/business/16876535.html. Retrieved 11 October 2008.
- ^ Three-finger salute[dead link]
- ^ Smith, Gina (3 December 2007). "Unsung innovators: David Bradley, inventor of the "three-finger salute"". Computerworld. http://www.computerworld.com/action/article.do?command=viewArticleBasic&articleId=9046742. Retrieved 12 April 2009.
- ^ "CTRL-ALT-DEL: The Three Finger Salute". Togaware. http://www.togaware.com/linux/survivor/CTRL_ALT_DEL_Three.html. Retrieved 12 April 2009.
- ^ "three fingered salute". Urban Dictionary. 2003. http://www.urbandictionary.com/define.php?term=three%20fingered%20salute. Retrieved 12 April 2009.
- ^ "Thank this guy for ‘control-alt-delete’". Indianapolis Star. http://www.gannettonline.com/e/trends/18001162.html. Retrieved 2010-09-09.
- ^ Wordspy cites the earliest such use as Chris Miksanek's 18 December 1995 Computerworld column titled, "Ctrl-Alt-Delete those holiday trinkets."
- ^ This doesn't work if there are logged-on users
- ^ Osterman, Larry (24 January 2005). "Why is Control-Alt-Delete the secure attention sequence (SAS)?". Larry Osterman's WebLog. MSDN Blogs. http://blogs.msdn.com/larryosterman/archive/2005/01/24/359850.aspx. Retrieved 15 March 2007.
- ^ "Mac OS X Server Easter Egg - This is not DOS". http://www.eeggs.com/items/11649.html. Retrieved 7 October 2011.
- ^ a b "Mac OS X keyboard shortcuts". Apple, Inc. http://support.apple.com/kb/HT1343.
- ^ See also "Mac OS X 10.4 or earlier: Computer stops responding". Apple, Inc. http://support.apple.com/kb/TS2298.
- ^ FOXTEL Set-Top Unit Reboot
- ^ "Frozen or unresponsive iPhone". http://www.apple.com/support/iphone/assistant/phone/#section_2.
- ^ "Billy Talent – 'Perfect World' Lyrics". http://www.sing365.com/music/lyric.nsf/perfect-world-lyrics-billy-talent/75d092b0796b50cd4825717b000dfea0. Retrieved 13 July 2011.
- ^ "Weird Al" Yankovic – 'it's all about the pentiums' Lyrics". http://www.sing365.com/music/lyric.nsf/It's-All-About-The-Pentiums-lyrics-Weird-Al-Yankovic/96D02B227DA29BF74825690E001FA259. Retrieved 26 October 2011.
- "Windows 3.1 Resource Kit SYSTEM.INI 386ENH Section A–L". Microsoft's KnowledgeBase article 83435. http://support.microsoft.com./kb/q83435/. Retrieved January 7, 2005.
- Linux manual pages for kill(2) and reboot(2).
- Gary S. Terhune (11 January 2004). "Lost Ctrl-Alt-Del function on W98, 2nd". microsoft.public.win98.gen_discussion. (Web link). — a report of the effect of
LocalRebootin Windows 95
- Geoff Chappell (6 May 1998). "Is this possible?". comp.os.ms-windows.programmer.vxd. (Web link). — a report of differences in
LocalRebootbetween Windows 3.x and Windows 95
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