SIGINT

SIGINT is an abbreviation that can refer to two distinct concepts in computing and intelligence. In Unix-like operating systems, SIGINT (signal interrupt) is a signal defined by the POSIX standard and is typically used to interrupt a running program. It is usually associated with the user pressing Ctrl-C in a terminal, which sends the signal to the foreground process group. The signal is commonly given the numeric value 2 on many systems, and the default action is to terminate the process. Programs may install a signal handler to catch, ignore, or perform cleanup when SIGINT is received, enabling graceful shutdowns. In contrast, signals such as SIGTERM and SIGQUIT differ in intent and default actions. SIGINT can also be sent programmatically via commands such as kill -INT <pid> or by sending signal 2 to a process.

SIGINT also stands for signals intelligence, the interception and analysis of signals for intelligence purposes. SIGINT covers both communications intelligence (COMINT) and electronic intelligence (ELINT), including interception of radio, telephone, satellite, radar, and other electronic emissions. It is collected by national security and military organizations and used to inform assessments of adversaries’ capabilities, intentions, and vulnerabilities. Techniques include interception and exploitation of signals, traffic analysis, cryptanalysis where feasible, and metadata correlation. SIGINT raises legal, ethical, and privacy considerations, varies across jurisdictions, and faces evolving challenges from encryption and rapid change in communications technologies.