.\" Copyright (c) 1994 SigmaSoft, Th. Lockert <firstname.lastname@example.org> .\" All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. The name of the author may not be used to endorse or promote products .\" derived from this software without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, .\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, .\" PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; .\" OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, .\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR .\" OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF .\" ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. .\" .\" $FreeBSD: src/lib/libc/gen/ftok.3,v 1.17 2009/07/13 12:53:43 trasz Exp $ .Dd July 9, 2009 .Os .Dt FTOK 3 .Sh NAME .Nm ftok .Nd create IPC identifier from path name .Sh LIBRARY .Lb libc .Sh SYNOPSIS .In sys/ipc.h .Ft key_t .Fn ftok "const char *path" "int id" .Sh DESCRIPTION The .Fn ftok function attempts to create a unique key suitable for use with the .Xr semget 2 , and .Xr shmget 2 functions, given the .Fa path of an existing file and a user-selectable .Fa id . .Pp The specified .Fa path must specify an existing file that is accessible to the calling process or the call will fail. Also, note that links to files will return the same key, given the same .Fa id . .Sh RETURN VALUES The .Fn ftok function will return -1 if .Fa path does not exist or if it cannot be accessed by the calling process. .Sh LEGACY SYNOPSIS .Fd #include <sys/types.h> .Fd #include <sys/ipc.h> .Pp The include file .In sys/types.h is necessary. .Sh SEE ALSO .Xr semget 2 , .Xr shmget 2 , .Xr compat 5 .Sh HISTORY The .Fn ftok function originates with System V and is typically used by programs that use the System V IPC routines. .Sh AUTHORS .An Thorsten Lockert Aq email@example.com .Sh BUGS The returned key is computed based on the device minor number and inode of the specified .Fa path , in combination with the lower 8 bits of the given .Fa id . Thus, it is quite possible for the routine to return duplicate keys.