Signal Concepts

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.

Signal may be sent to a process by the kernel, by another process, or by itself. There is a range of standard signal types, each of which has a unique number and purpose.

• They are defined in MACRO as SIGXXX(number defined from 1 to 31 usually)

By default, a signal either is ignored, terminates a process (with or without a core dump), stops a running process, or restarts a stopped process.

kill()

One process can send a signal to another process using the kill() system call, which is the analog of the kill shell command.

int kill(pid_t pid, int sig); //Returns 0 on success, or –1 on error