1.\" $NetBSD: ftok.3,v 1.9 2002/10/01 16:48:34 wiz 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 June 24, 1994 29.Os 30.Dt FTOK 3 31.Sh NAME 32.Nm ftok 33.Nd create IPC indentifier from path name 34.Sh LIBRARY 35.Lb libc 36.Sh SYNOPSIS 37.Fd #include \*[Lt]sys/types.h\*[Gt] 38.Fd #include \*[Lt]sys/ipc.h\*[Gt] 39.Ft key_t 40.Fn ftok "const char *path" "int id" ; 41.Sh DESCRIPTION 42The 43.Fn ftok 44function attempts to create a unique key suitable for use with the 45.Xr msgget 2 , 46.Xr semget 2 47and 48.Xr shmget 2 49functions given the 50.Fa path 51of an existing file and a user-selectable 52.Fa id . 53.Pp 54The specified 55.Fa path 56must specify an existing file that is accessible to the calling process 57or the call will fail. 58Also, note that links to files will return the same key, given the same 59.Fa id . 60.Pp 61Only the 8 least significant bits of 62.Fa id 63are used in the key generation; the rest of the bits are ignored. 64.Sh RETURN VALUES 65The 66.Fn ftok 67function will return ((key_t)-1) if 68.Fa path 69does not exist or if it cannot be accessed by the calling process. 70.Sh SEE ALSO 71.Xr msgget 2 , 72.Xr semget 2 , 73.Xr shmget 2 74.Sh HISTORY 75The 76.Fn ftok 77function originated with System V and is typically used by programs 78that use the System V IPC routines. 79.Sh AUTHORS 80.Bl -tag 81Thorsten Lockert \*[Lt]tholo@sigmasoft.com\*[Gt] 82.El 83.Sh BUGS 84The returned key is computed based on the device and inode of the 85specified 86.Fa path 87in combination with the given 88.Fa id . 89Thus it is quite possible for the routine to return duplicate keys 90given that those fields are not 8- and 16-bit quantities like they 91were on System V based systems where this library routine's ancestor 92were originally created. 93