signal11

Signal 11, commonly referred to as SIGSEGV (segmentation fault), is a signal defined by POSIX and used on many Unix-like systems to indicate an invalid memory reference. The number 11 is the conventional signal number for SIGSEGV on Linux and most BSD variants, though signal numbering can vary across platforms. It is delivered by the kernel to a process when it detects a memory access violation.

SIGSEGV occurs when a program attempts to access memory it is not allowed to access. Typical causes include dereferencing a null or uninitialized pointer, reading or writing beyond the bounds of an array, using a pointer after it has been freed, or attempting to execute data that is not marked executable. In some cases, hardware faults or misbehaving memory-mapped I/O can also trigger a segmentation fault. The fault is raised by the memory protection system during an access attempt.

The default action for SIGSEGV is to terminate the offending process and, if enabled, produce a core dump to aid debugging. Programs can install a custom signal handler for SIGSEGV using mechanisms such as sigaction, but reliably recovering from a segmentation fault is generally not possible and continuing execution after a fault is risky and often leads to undefined behavior.

Debugging and prevention techniques include using core dumps with debuggers like gdb, as well as memory-analysis tools such as AddressSanitizer, ThreadSanitizer, and Valgrind. Preventative measures include writing safer code, employing languages with memory safety guarantees, performing thorough bounds checking, and adopting robust testing practices to catch memory errors early.