Advanced UNIX Programming

Destroying Memory Mappings

With the exception of the MAP_INHERIT flag for FreeBSD, the memory-mapped regions are unmapped automatically by the kernel when execve(2) is called or when the process terminates. It may occur in an application, however, that the memory-mapped file is needed only temporarily. The munmap(2) system call is used to unmap it:

#include <sys/types.h>
#include <sys/mman.h>

int munmap(void *addr, size_t len);

The memory region to be unmapped is specified as the region starting at addr for a length of len bytes. The function munmap(2) returns 0 when successful. Otherwise, -1 is returned, with an error code left in errno. It should be noted that this system call does not cause pending changes to be written out to the file. ...