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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 1.17 2009/07/13 12:53:43 trasz Exp $
27.Dd July 9, 2009
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 semget 2 ,
44and
45.Xr shmget 2
46functions, given the
47.Fa path
48of an existing file and a user-selectable
49.Fa id .
50.Pp
51The specified
52.Fa path
53must specify an existing file that is accessible to the calling process
54or the call will fail.
55Also, note that links to files will return the
56same key, given the same
57.Fa id .
58.Sh RETURN VALUES
59The
60.Fn ftok
61function will return -1 if
62.Fa path
63does not exist or if it cannot be accessed by the calling process.
64.Sh LEGACY SYNOPSIS
65.Fd #include <sys/types.h>
66.Fd #include <sys/ipc.h>
67.Pp
68The include file
69.In sys/types.h
70is necessary.
71.Sh SEE ALSO
72.Xr semget 2 ,
73.Xr shmget 2 ,
74.Xr compat 5
75.Sh HISTORY
76The
77.Fn ftok
78function originates with System V and is typically used by programs
79that use the System V IPC routines.
80.Sh AUTHORS
81.An Thorsten Lockert Aq tholo@sigmasoft.com
82.Sh BUGS
83The returned key is computed based on the device minor number and inode
84of the specified
85.Fa path ,
86in combination with the lower 8 bits of the given
87.Fa id .
88Thus, it is quite possible for the routine to return duplicate keys.