1.\"	$OpenBSD: ftok.3,v 1.17 2014/11/15 22:22:09 guenther Exp $
2.\"
3.\" Copyright (c) 1994 SigmaSoft, Th. Lockert <tholo@sigmasoft.com>
4.\" All rights reserved.
5.\"
6.\" Redistribution and use in source and binary forms, with or without
7.\" modification, are permitted provided that the following conditions
8.\" are met:
9.\" 1. Redistributions of source code must retain the above copyright
10.\"    notice, this list of conditions and the following disclaimer.
11.\" 2. Redistributions in binary form must reproduce the above copyright
12.\"    notice, this list of conditions and the following disclaimer in the
13.\"    documentation and/or other materials provided with the distribution.
14.\" 3. The name of the author may not be used to endorse or promote products
15.\"    derived from this software without specific prior written permission.
16.\"
17.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
18.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
19.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
20.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
21.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
22.\" PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
23.\" OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
24.\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
25.\" OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
26.\" ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27.\"
28.Dd $Mdocdate: November 15 2014 $
29.Dt FTOK 3
30.Os
31.Sh NAME
32.Nm ftok
33.Nd create IPC identifier from a pathname
34.Sh SYNOPSIS
35.In sys/ipc.h
36.Ft key_t
37.Fn ftok "const char *path" "int id"
38.Sh DESCRIPTION
39The
40.Fn ftok
41function attempts to create a unique key suitable for use with the
42.Xr msgget 2 ,
43.Xr semget 2
44and
45.Xr shmget 2
46functions given the
47.Fa path
48of an existing file and a user-selectable
49.Fa id .
50.Pp
51The specified
52.Fa path
53must refer to an existing file that is accessible to the calling process
54or the call will fail.
55Also, note that links to files will return the same key, given the same
56.Fa id .
57Only the 8 least significant bits of
58.Fa id
59are used in the key generation; the rest of the bits are ignored.
60.Sh RETURN VALUES
61The
62.Fn ftok
63function will return (key_t)\-1 if
64.Fa path
65does not exist or if it cannot be accessed by the calling process.
66.Sh SEE ALSO
67.Xr msgget 2 ,
68.Xr semget 2 ,
69.Xr shmget 2
70.Sh HISTORY
71The
72.Fn ftok
73function originated with System V and is typically used by programs
74that use the System V IPC routines.
75.Sh AUTHORS
76.An Thorsten Lockert Aq Mt tholo@sigmasoft.com
77.Sh BUGS
78The returned key is computed based on the device and inode of the
79specified
80.Fa path
81in combination with the given
82.Fa id .
83Thus it is quite possible for the routine to return duplicate keys
84given that those fields are not 8- and 16-bit quantities like they
85were on System V based systems where this library routine's ancestors
86were originally created.
87