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[dragonfly.git] / lib / libc / gen / ftok.3
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1.\" Copyright (c) 1994 SigmaSoft, Th. Lockert <tholo@sigmasoft.com>
2.\" All rights reserved.
3.\"
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26.\" $FreeBSD: src/lib/libc/gen/ftok.3,v 1.12.2.3 2003/05/07 00:30:26 tjr 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/types.h
37.In sys/ipc.h
38.Ft key_t
39.Fn ftok "const char *path" "int id"
40.Sh DESCRIPTION
41The
42.Fn ftok
43function attempts to create a unique key suitable for use with the
44.Xr msgget 3 ,
45.Xr semget 2
46and
47.Xr shmget 2
48functions given the
49.Fa path
50of an existing file and a user-selectable
51.Fa id .
52.Pp
53The specified
54.Fa path
55must specify an existing file that is accessible to the calling process
56or the call will fail. Also, 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 semget 2 ,
67.Xr shmget 2 ,
68.Xr msgget 3
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 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.