1.\" $NetBSD: ftok.3,v 1.18 2014/03/18 18:20:37 riastradh 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.\" 15.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 16.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 17.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 18.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 19.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, 20.\" PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; 21.\" OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, 22.\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR 23.\" OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF 24.\" ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 25.\" 26.Dd April 27, 2010 27.Dt FTOK 3 28.Os 29.Sh NAME 30.Nm ftok 31.Nd create IPC identifier from path name 32.Sh LIBRARY 33.Lb libc 34.Sh SYNOPSIS 35.In sys/types.h 36.In sys/ipc.h 37.Ft key_t 38.Fn ftok "const char *path" "int 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. 56Also, note that links to files will return the same key, given the same 57.Fa id . 58.Pp 59Only the 8 least significant bits of 60.Fa id 61are used in the key generation; the rest of the bits are ignored. 62.Sh RETURN VALUES 63The 64.Fn ftok 65function will return ((key_t)-1) if 66.Fa path 67does not exist or if it cannot be accessed by the calling process. 68.Sh SEE ALSO 69.Xr msgget 2 , 70.Xr semget 2 , 71.Xr shmget 2 72.Sh STANDARDS 73The 74.Fn ftok 75function conforms to 76.St -p1003.1 . 77.Sh HISTORY 78The 79.Fn ftok 80function originated with System V and is typically used by programs 81that use the System V IPC routines. 82.Sh AUTHORS 83.An Thorsten Lockert Aq Mt tholo@sigmasoft.com 84.Sh BUGS 85The returned key is computed based on the device and inode of the 86specified 87.Fa path 88in combination with the given 89.Fa id . 90Thus it is quite possible for the routine to return duplicate keys 91given that those fields are not 8- and 16-bit quantities like they 92were on System V based systems where this library routine's ancestor 93were originally created. 94