6.1 Default action

Most application programs do not specify a handler for each possible signal. In the case of not having an explicit handler, application programs inherit default actions.

There are different actions for different types of signals:

• term: this means “termination”. If this type of signal is not intercepted, the signaled process is terminated by the OS.
• ign: this means “ignored”. If this type of signal is not intercepted, the signal is safely ignore.
• core: this means a “core dump” after termination. Core dump is an OS feature to write the entire memory space of a process to a file for post mortem analysis.
• stop: a process is stopped (paused, suspended) if this signal is not intercepted.
• cont: a previously stopped process resumes (continues) if this signal is not intercepted.

The default action can be overriden sometimes by a process. A process can “catch” a signal by specifying a handler. This gives a process a chance to use its own logic to determine what needs to be done in response to a system generated signal.

A process can also configure signals as “ignored”. A process does not have the privilege to change all types of signals to be ignored, only some of the available signals.