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.Dd November 28, 2022 26.Dt FTOK 3 27.Os 28.Sh NAME 29.Nm ftok 30.Nd create IPC identifier from path name 31.Sh LIBRARY 32.Lb libc 33.Sh SYNOPSIS 34.In sys/ipc.h 35.Ft key_t 36.Fn ftok "const char *path" "int id" 37.Sh DESCRIPTION 38The 39.Fn ftok 40function attempts to create a unique key suitable for use with the 41.Xr msgget 2 , 42.Xr semget 2 43and 44.Xr shmget 2 45functions given the 46.Fa path 47of an existing file and a user-selectable 48.Fa id . 49.Pp 50The specified 51.Fa path 52must specify an existing file that is accessible to the calling process 53or the call will fail. 54Also, note that links to files will return the 55same key, given the same 56.Fa id . 57.Sh RETURN VALUES 58The 59.Fn ftok 60function will return -1 if 61.Fa path 62does not exist or if it cannot be accessed by the calling process. 63.Sh SEE ALSO 64.Xr msgget 2 , 65.Xr semget 2 , 66.Xr shmget 2 67.Sh HISTORY 68The 69.Fn ftok 70function originates with System V and is typically used by programs 71that use the System V IPC routines. 72.Sh AUTHORS 73.An Thorsten Lockert Aq Mt tholo@sigmasoft.com 74.Sh BUGS 75The returned key is computed based on the device minor number and inode of the 76specified 77.Fa path 78in combination with the lower 8 bits of the given 79.Fa id . 80Thus it is quite possible for the routine to return duplicate keys. 81