CtrlAltDelete

Ctrl+Alt+Delete, often written as CtrlAltDelete, is a keyboard shortcut that interrupts the normal flow of a computer program and triggers a system-level response. It is a security attention sequence (SAS) intended to be processed by the operating system rather than by any application, allowing secure access to login prompts or system dialogs even when software is unresponsive.

Origins of the sequence lie in early IBM PC hardware and BIOS design, where a distinct key combination could be asserted at a low level. Microsoft and other operating system developers adopted and adapted the SAS to provide a controlled way to request user authentication or access critical management tools without interception by user programs.

In Windows, pressing Ctrl+Alt+Delete typically opens a security screen or login prompt. Depending on version and configuration, options may include Lock, Switch User, Sign out, Task Manager, or a password login. The sequence is treated with higher privilege than normal input to prevent interference from running applications.

In many Linux and Unix-like systems, the behavior of Ctrl+Alt+Delete is configurable. By default, it can reboot the machine via the init or systemd control targets, but administrators can rebind it to run scripts, suspend, or do nothing. Desktop environments may also map the shortcut to account-level actions.

Security and design considerations: because the SAS is handled by the OS, it helps protect against malware that might try to imitate a login prompt or terminate a frozen application. However, it is not a universal safeguard; configurations vary, and on some systems the sequence may immediately reboot or do nothing, potentially leading to data loss if used inadvertently.

See also: Secure Attention Sequence.