What is default signal handler?

Signals are software interrupts sent to a program to indicate that an important event has occurred. Every signal in Unix-like operating systems can be handled by one of two possible handlers:

• A default signal handler
• A user-defined signal handler

A Default signal handler is a predefined handler associated with every signal that the kernel automatically invokes when a process receives that signal. When a program doesn't specify custom handling for a particular signal, the operating system uses the default handler to perform a predetermined action.

Types of Default Actions

Default signal handlers can perform one of several standard actions when a signal is received:

• Terminate − End the process immediately

• Ignore − Discard the signal and continue execution

• Core Dump − Terminate the process and create a core file containing the memory image for debugging

• Stop − Suspend the process execution

• Continue − Resume a previously stopped process

Common Signals and Their Default Actions

How Default Handlers Work

When a signal is delivered to a process, the kernel checks if the process has installed a custom signal handler. If no custom handler exists, the kernel invokes the default handler associated with that signal. The default handler executes the predefined action immediately without any user intervention.

For example, when a process receives SIGTERM, the default handler terminates the process gracefully. If the process receives SIGSEGV due to invalid memory access, the default handler terminates the process and generates a core dump for debugging purposes.

Conclusion

Default signal handlers provide standardized responses to system events when programs don't define custom behavior. They ensure consistent system behavior and help maintain process control, making signal handling predictable across Unix-like operating systems.