1.\" $OpenBSD: ftok.3,v 1.3 1996/10/02 13:51:34 michaels 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 SYNOPSIS 35.Fd #include <sys/types.h> 36.Fd #include <sys/ipc.h> 37.Ft key_t 38.Fn ftok "const char *path" "char id" ; 39.Sh DESCRIPTION 40The 41.Fn ftok 42function attempts to create a unique key suitable for use with the 43.Xr msgget 2 , 44.Xr semget 2 45and 46.Xr shmget 2 47functions given the 48.Fa path 49of an existing file and a user-selectable 50.Fa id . 51.Pp 52The specified 53.Fa path 54must specify an existing file that is accessible to the calling process 55or the call will fail. Also, note that links to files will return the 56same key, given the same 57.Fa id . 58.Sh RETURN VALUES 59The 60.Fn ftok 61function will return -1 if 62.Fa path 63does not exist or if it cannot be accessed by the calling process. 64.Sh SEE ALSO 65.Xr msgget 2 , 66.Xr semget 2 , 67.Xr shmget 2 68.Sh HISTORY 69The 70.Fn ftok 71function originated with System V and is typically used by programs 72that use the System V IPC routines. 73.Sh AUTHOR 74.Bl -tag 75Thorsten Lockert <tholo@sigmasoft.com> 76.El 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