1.\" Copyright (c) 1994 SigmaSoft, Th. Lockert <tholo@sigmasoft.com> 2.\" All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. The name of the author may not be used to endorse or promote products 13.\" derived from this software without specific prior written permission. 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.\" $FreeBSD: src/lib/libc/gen/ftok.3,v 1.12.2.3 2003/05/07 00:30:26 tjr Exp $ 27.\" 28.Dd June 24, 1994 29.Dt FTOK 3 30.Os 31.Sh NAME 32.Nm ftok 33.Nd create IPC identifier from path name 34.Sh LIBRARY 35.Lb libc 36.Sh SYNOPSIS 37.In sys/types.h 38.In sys/ipc.h 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 3 , 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. Also, note that links to files will return the 58same key, given the same 59.Fa id . 60.Sh RETURN VALUES 61The 62.Fn ftok 63function will return -1 if 64.Fa path 65does not exist or if it cannot be accessed by the calling process. 66.Sh SEE ALSO 67.Xr semget 2 , 68.Xr shmget 2 , 69.Xr msgget 3 70.Sh HISTORY 71The 72.Fn ftok 73function originates 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 minor number and inode of the 79specified 80.Fa path 81in combination with the lower 8 bits of the given 82.Fa id . 83Thus it is quite possible for the routine to return duplicate keys. 84