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20. Signals: Fundamental Concepts > Concepts and Overview

Concepts and Overview

A signal is a notification to a process that an event has occurred. Signals are sometimes described as software interrupts. Signals are analogous to hardware interrupts in that they interrupt the normal flow of execution of a program; in most cases, it is not possible to predict exactly when a signal will arrive.

One process can (if it has suitable permissions) send a signal to another process. In this use, signals can be employed as a synchronization technique, or even as a primitive form of interprocess communication (IPC). It is also possible for a process to send a signal to itself. However, the usual source of many signals sent to a process is the kernel. Among the types of events that cause the kernel to generate a signal for a process are the following:


  

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