munmap —
remove a mapping
Standard C Library (libc, -lc)
#include <sys/mman.h>
int
  
  munmap(void
    *addr, size_t
  len);
The munmap() system call deletes the mappings for the
  specified address range, and causes further references to addresses within the
  range to generate invalid memory references.
Upon successful completion, munmap returns zero.
  Otherwise, a value of -1 is returned and errno is set to
  indicate the error.
munmap() will fail if:
  - [EINVAL]
- The addr parameter was not page aligned, or some
      part of the region being unmapped is outside the valid address range for a
      process.
Themunmap() function conforms to IEEE
  Std 1003.1b-1993 (“POSIX.1b”).
The munmap() function first appeared in
  4.4BSD.