.\"
.\" Copyright (c) 2008 Apple Inc.  All rights reserved.
.\"
.\" @APPLE_LICENSE_HEADER_START@
.\" 
.\" This file contains Original Code and/or Modifications of Original Code
.\" as defined in and that are subject to the Apple Public Source License
.\" Version 2.0 (the 'License'). You may not use this file except in
.\" compliance with the License. Please obtain a copy of the License at
.\" http://www.opensource.apple.com/apsl/ and read it before using this
.\" file.
.\" 
.\" The Original Code and all software distributed under the License are
.\" distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
.\" EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
.\" INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
.\" FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
.\" Please see the License for the specific language governing rights and
.\" limitations under the License.
.\" 
.\" @APPLE_LICENSE_HEADER_END@
.\"
.\"
.\"	$NetBSD: munmap.2,v 1.5 1995/02/27 12:35:03 cgd Exp $
.\"
.\" Copyright (c) 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	This product includes software developed by the University of
.\"	California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"	@(#)munmap.2	8.2 (Berkeley) 4/15/94
.\"
.Dd October 16, 2008
.Dt MUNMAP 2
.Os
.Sh NAME
.Nm munmap
.Nd remove a mapping
.Sh SYNOPSIS
.Fd #include <sys/mman.h>
.Ft int
.Fo munmap
.Fa "void *addr"
.Fa "size_t len"
.Fc
.Sh DESCRIPTION
The
.Fn munmap
system call
deletes the mappings for the specified address range,
causing further references to addresses within the range
to generate invalid memory references.
.Sh DIRTY PAGE HANDLING
How
.Fn munmap
handles a dirty page, depends on what type of memory is being unmapped:
.Pp
.Bl -tag -width "[System V Shared]"
.It Bq 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.
.It Bq 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.
.It Bq 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 
.Xr msync 2 .
.El
.Pp
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).
.Sh RETURN VALUES
Upon successful completion,
.Nm munmap
returns zero.
Otherwise, a value of -1 is returned and
.Va errno
is set to indicate the error.
.Sh ERRORS
.Fn Munmap
will fail if:
.Bl -tag -width Er
.\" ===========
.It Bq Er EINVAL
The
.Fa addr
parameter was not page aligned (i.e., a multiple of the page size).
.\" ===========
.It Bq Er EINVAL
The
.Fa len
parameter was negative or zero.
.\" ===========
.It Bq Er EINVAL
Some part of the region being unmapped is not part of the currently
valid address space.
.El
.Sh LEGACY SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <sys/mman.h>
.Pp
The include file
.In sys/types.h
is necessary.
.Pp
.Ft int
.br
.Fo munmap
.Fa "caddr_t addr"
.Fa "size_t len"
.Fc ;
.Pp
The type of
.Fa addr
has changed.
.Sh "SEE ALSO"
.Xr getpagesize 3 ,
.Xr msync 2 ,
.Xr munmap 2 ,
.Xr mprotect 2 ,
.Xr madvise 2 ,
.Xr mincore 2 ,
.Xr compat 5
.Sh HISTORY
The
.Fn munmap
function first appeared in 4.4BSD.