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munmap(2) [mojave man page]

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 generate 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 reference 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 multiple 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

Check Out this Related Man Page

MUNMAP(3P)						     POSIX Programmer's Manual							MUNMAP(3P)

PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the correspond- ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux. NAME
munmap - unmap pages of memory SYNOPSIS
#include <sys/mman.h> int munmap(void *addr, size_t len); DESCRIPTION
The munmap() function shall remove any mappings for those entire pages containing any part of the address space of the process starting at addr and continuing for len bytes. Further references to these pages shall result in the generation of a SIGSEGV signal to the process. If there are no mappings in the specified address range, then munmap() has no effect. The implementation shall require that addr be a multiple of the page size {PAGESIZE}. If a mapping to be removed was private, any modifications made in this address range shall be discarded. Any memory locks (see mlock() and mlockall()) associated with this address range shall be removed, as if by an appropriate call to munlock(). If a mapping removed from a typed memory object causes the corresponding address range of the memory pool to be inaccessible by any process in the system except through allocatable mappings (that is, mappings of typed memory objects opened with the POSIX_TYPED_MEM_MAP_ALLOCAT- ABLE flag), then that range of the memory pool shall become deallocated and may become available to satisfy future typed memory allocation requests. A mapping removed from a typed memory object opened with the POSIX_TYPED_MEM_MAP_ALLOCATABLE flag shall not affect in any way the avail- ability of that typed memory for allocation. The behavior of this function is unspecified if the mapping was not established by a call to mmap(). RETURN VALUE
Upon successful completion, munmap() shall return 0; otherwise, it shall return -1 and set errno to indicate the error. ERRORS
The munmap() function shall fail if: EINVAL Addresses in the range [addr,addr+len) are outside the valid range for the address space of a process. EINVAL The len argument is 0. EINVAL The addr argument is not a multiple of the page size as returned by sysconf(). The following sections are informative. EXAMPLES
None. APPLICATION USAGE
The munmap() function is only supported if the Memory Mapped Files option or the Shared Memory Objects option is supported. RATIONALE
The munmap() function corresponds to SVR4, just as the mmap() function does. It is possible that an application has applied process memory locking to a region that contains shared memory. If this has occurred, the munmap() call ignores those locks and, if necessary, causes those locks to be removed. FUTURE DIRECTIONS
None. SEE ALSO
mlock(), mlockall(), mmap(), posix_typed_mem_open(), sysconf(), the Base Definitions volume of IEEE Std 1003.1-2001, <signal.h>, <sys/mman.h> COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol- ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html . IEEE
/The Open Group 2003 MUNMAP(3P)

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