MUNMAP(2)                   BSD System Calls Manual                  MUNMAP(2)

NAME
     munmap -- remove a mapping

SYNOPSIS
     #include <sys/mman.h>

     int
     munmap(void *addr, size_t len);

DESCRIPTION
     The munmap() system call deletes the mappings for the specified address
     range, causing further references to addresses within the range to gener-
     ate invalid memory references.

DIRTY PAGE HANDLING
     How munmap() handles a dirty page, depends on what type of memory is
     being unmapped:

     [Anonymous]        If the memory is anonymous memory and if the last ref-
                        erence is going away, then the contents are discarded
                        by definition of anonymous memory.

     [System V Shared]  If the memory mapping was created using System V
                        shared memory, then the contents persist until the
                        System V memory region is destroyed or the system is
                        rebooted.

     [File mapping]     If the mapping maps data from a file (MAP_SHARED),
                        then the memory will eventually be written back to
                        disk if it's dirty.  This will happen automatically at
                        some point in the future (implementation dependent).
                        Note: to force the memory to be written back to the
                        disk, use msync(2).

     If there are still other references to the memory when the munmap is
     done, then nothing is done to the memory itself and it may be swapped out
     if need be. The memory will continue to persist until the last reference
     goes away (except for System V shared memory in which case, see above).

RETURN VALUES
     Upon successful completion, munmap returns zero.  Otherwise, a value of
     -1 is returned and errno is set to indicate the error.

ERRORS
     munmap() will fail if:

     [EINVAL]           The addr parameter was not page aligned (i.e., a mul-
                        tiple of the page size).

     [EINVAL]           The len parameter was negative or zero.

     [EINVAL]           Some part of the region being unmapped is not part of
                        the currently valid address space.

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

     The include file <sys/types.h> is necessary.

     int
     munmap(caddr_t addr, size_t len);

     The type of addr has changed.

SEE ALSO
     getpagesize(3), msync(2), munmap(2), mprotect(2), madvise(2), mincore(2),
     compat(5)

HISTORY
     The munmap() function first appeared in 4.4BSD.

BSD                            October 16, 2008                            BSD