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1.\" Copyright (c) 1994 SigmaSoft, Th. Lockert <tholo@sigmasoft.com>
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26.\" $FreeBSD: src/lib/libc/gen/ftok.3,v 1.16 2004/07/02 23:52:10 ru Exp $
27.Dd June 24, 1994
28.Os
29.Dt FTOK 3
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 3 ,
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 LEGACY SYNOPSIS
66.Fd #include <sys/types.h>
67.Fd #include <sys/ipc.h>
68.Pp
69The include file
70.In sys/types.h
71is necessary.
72.Sh SEE ALSO
73.Xr semget 2 ,
74.Xr shmget 2 ,
75.Xr msgget 3 ,
76.Xr compat 5
77.Sh HISTORY
78The
79.Fn ftok
80function originates with System V and is typically used by programs
81that use the System V IPC routines.
82.Sh AUTHORS
83.An Thorsten Lockert Aq tholo@sigmasoft.com
84.Sh BUGS
85The returned key is computed based on the device minor number and inode
86of the specified
87.Fa path ,
88in combination with the lower 8 bits of the given
89.Fa id .
90Thus, it is quite possible for the routine to return duplicate keys.