MUNMAP(2) BSD System Calls Manual MUNMAP(2)NAMEmunmap — 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.
ERRORSMunmap() 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 ALSOgetpagesize(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
