This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
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 may require that addr be a multiple of the page
size as returned by sysconf().
If a mapping to be removed was private, any modifications made in
this address range shall be discarded.
Any memory locks (see mlock(3p) and mlockall(3p)) associated with
this address range shall be removed, as if by an appropriate call to
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_ALLOCATABLE 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
availability of that typed memory for allocation.
The behavior of this function is unspecified if the mapping was not
established by a call to mmap().
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.
The munmap() function may fail if:
EINVAL The addr argument is not a multiple of the page size as
returned by sysconf().
The following sections are informative.
The munmap() function corresponds to SVR4, just as the mmap()
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.
Most implementations require that addr is a multiple of the page size
as returned by sysconf().
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) 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.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the
source files to man page format. To report such errors, see
IEEE/The Open Group 2013 MUNMAP(3P)