Manpages - munmap.3p

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.

munmap — unmap pages of memory

  #include <sys/mman.h>
  int munmap(void *addr, size_t len);

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/().

Upon successful completion, munmap/() shall return 0; otherwise, it shall return -1 and set /errno to indicate the error.

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.

None.

None.

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/().

None.

/mlock ( )/, /mlockall ( )/, /mmap ( )/, /posix_typed_mem_open ( )/, /sysconf ( )/

The Base Definitions volume of POSIX.1‐2017, <sys_mman.h>

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 .

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