SIGSEGV This! (Cont.) The Designers of the Unix operating system decided that this situation indicates a program bug, and thus instead of automatically allocating a page on-the-fly, the operating system delivers a signal to the process - a SEGV signal. Another method of getting a SEGV signal, is trying to access an area of memory which is defined as illegal for virtual memory. Since many invalid pointer problems occur with very low pointer values (e.g. NULL, which is 0), the first segment of virtual memory is never mapped. Attempts to access this segment will lead to a SEGV signal.