Merge from vendor branch BZIP:
[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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15.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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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 $
1de703da 27.\" $DragonFly: src/lib/libc/gen/ftok.3,v 1.2 2003/06/17 04:26:42 dillon Exp $
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28.Dd June 24, 1994
29.Os
30.Dt FTOK 3
31.Sh NAME
32.Nm ftok
33.Nd create IPC identifier from path name
34.Sh LIBRARY
35.Lb libc
36.Sh SYNOPSIS
37.In sys/types.h
38.In sys/ipc.h
39.Ft key_t
40.Fn ftok "const char *path" "int id"
41.Sh DESCRIPTION
42The
43.Fn ftok
44function attempts to create a unique key suitable for use with the
45.Xr msgget 3 ,
46.Xr semget 2
47and
48.Xr shmget 2
49functions given the
50.Fa path
51of an existing file and a user-selectable
52.Fa id .
53.Pp
54The specified
55.Fa path
56must specify an existing file that is accessible to the calling process
57or the call will fail. Also, note that links to files will return the
58same key, given the same
59.Fa id .
60.Sh RETURN VALUES
61The
62.Fn ftok
63function will return -1 if
64.Fa path
65does not exist or if it cannot be accessed by the calling process.
66.Sh SEE ALSO
67.Xr semget 2 ,
68.Xr shmget 2 ,
69.Xr msgget 3
70.Sh HISTORY
71The
72.Fn ftok
73function originates with System V and is typically used by programs
74that use the System V IPC routines.
75.Sh AUTHORS
76.An Thorsten Lockert Aq tholo@sigmasoft.com
77.Sh BUGS
78The returned key is computed based on the device minor number and inode of the
79specified
80.Fa path
81in combination with the lower 8 bits of the given
82.Fa id .
83Thus it is quite possible for the routine to return duplicate keys.