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.\" $FreeBSD$ 27.Dd November 28, 2022 28.Dt FTOK 3 29.Os 30.Sh NAME 31.Nm ftok 32.Nd create IPC identifier from path name 33.Sh LIBRARY 34.Lb libc 35.Sh SYNOPSIS 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 57same key, given the same 58.Fa id . 59.Sh RETURN VALUES 60The 61.Fn ftok 62function will return -1 if 63.Fa path 64does not exist or if it cannot be accessed by the calling process. 65.Sh SEE ALSO 66.Xr msgget 2 , 67.Xr semget 2 , 68.Xr shmget 2 69.Sh HISTORY 70The 71.Fn ftok 72function originates with System V and is typically used by programs 73that use the System V IPC routines. 74.Sh AUTHORS 75.An Thorsten Lockert Aq Mt tholo@sigmasoft.com 76.Sh BUGS 77The returned key is computed based on the device minor number and inode of the 78specified 79.Fa path 80in combination with the lower 8 bits of the given 81.Fa id . 82Thus it is quite possible for the routine to return duplicate keys. 83