gen/FreeBSD/ftok.3

   1 .\" Copyright (c) 1994 SigmaSoft, Th. Lockert <tholo@sigmasoft.com>
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  26 .\" $FreeBSD: src/lib/libc/gen/ftok.3,v 1.15 2002/10/19 13:33:12 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
  41 The
  42 .Fn ftok
  43 function attempts to create a unique key suitable for use with the
  44 .Xr msgget 3 ,
  45 .Xr semget 2
  46 and
  47 .Xr shmget 2
  48 functions given the
  49 .Fa path
  50 of an existing file and a user-selectable
  51 .Fa id .
  52 .Pp
  53 The specified
  54 .Fa path
  55 must specify an existing file that is accessible to the calling process
  56 or the call will fail.  Also, note that links to files will return the
  57 same key, given the same
  58 .Fa id .
  59 .Sh RETURN VALUES
  60 The
  61 .Fn ftok
  62 function will return -1 if
  63 .Fa path
  64 does 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
  70 The
  71 .Fn ftok
  72 function originates with System V and is typically used by programs
  73 that use the System V IPC routines.
  74 .Sh AUTHORS
  75 .An Thorsten Lockert Aq tholo@sigmasoft.com
  76 .Sh BUGS
  77 The returned key is computed based on the device minor number and inode of the
  78 specified
  79 .Fa path
  80 in combination with the lower 8 bits of the given
  81 .Fa id .
  82 Thus it is quite possible for the routine to return duplicate keys.