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PROLOG
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.
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 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() 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_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().
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.
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.
EXAMPLES
None.
APPLICATION USAGE
None.
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.
Most implementations require that addr is a multiple of the page size as returned by sysconf().
FUTURE DIRECTIONS
None.
SEE ALSO
mlock(), mlockall(), mmap(), posix_typed_mem_open(), sysconf()
The Base Definitions volume of POSIX.1‐2017, <sys_mman.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .
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
https://www.kernel.org/doc/man-pages/reporting_bugs.html .