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.\" $OpenBSD: ftok.3,v 1.14 2007/05/31 19:19:28 jmc Exp $
.\"
.\" Copyright (c) 1994 SigmaSoft, Th. Lockert <tholo@sigmasoft.com>
.\" 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. The name of the author may not be used to endorse or promote products
.\" derived from this software without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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.
.\"
.Dd $Mdocdate: May 31 2007 $
.Dt FTOK 3
.Os
.Sh NAME
.Nm ftok
.Nd create IPC identifier from a pathname
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <sys/ipc.h>
.Ft key_t
.Fn ftok "const char *path" "int id"
.Sh DESCRIPTION
The
.Fn ftok
function attempts to create a unique key suitable for use with the
.Xr msgget 2 ,
.Xr semget 2
and
.Xr shmget 2
functions given the
.Fa path
of an existing file and a user-selectable
.Fa id .
.Pp
The specified
.Fa path
must refer to an existing file that is accessible to the calling process
or the call will fail.
Also, note that links to files will return the same key, given the same
.Fa id .
Only the 8 least significant bits of
.Fa id
are used in the key generation; the rest of the bits are ignored.
.Sh RETURN VALUES
The
.Fn ftok
function will return (key_t)\-1 if
.Fa path
does not exist or if it cannot be accessed by the calling process.
.Sh SEE ALSO
.Xr msgget 2 ,
.Xr semget 2 ,
.Xr shmget 2
.Sh HISTORY
The
.Fn ftok
function originated with System V and is typically used by programs
that use the System V IPC routines.
.Sh AUTHORS
.An Thorsten Lockert Aq tholo@sigmasoft.com
.Sh BUGS
The returned key is computed based on the device and inode of the
specified
.Fa path
in combination with the given
.Fa id .
Thus it is quite possible for the routine to return duplicate keys
given that those fields are not 8- and 16-bit quantities like they
were on System V based systems where this library routine's ancestors
were originally created.
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