A signal is a notification to a process that an event has occurred. Signals usually occur asynchronously. This means that the process doesn t know ahead of time exactly when a signal will occur. By the kernel to a process.
Every signal has a disposition, which is also called the action associated with the signal.
The disposition of a signal can be set by calling the signaction function. There are three choices for the disposition. Provide the function whenever a specific signal occurs. This function is the signal handler, and this action is called catching the signal. The default is normally to terminate a process on the receipt of a signal, with certain signals also generating a core image of the process in its working directory.