gen/ftok.3

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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
  40 The
  41 .Fn ftok
  42 function attempts to create a unique key suitable for use with the
  43 .Xr msgget 3 ,
  44 .Xr semget 2 ,
  45 and
  46 .Xr shmget 2
  47 functions, given the
  48 .Fa path
  49 of an existing file and a user-selectable
  50 .Fa id .
  51 .Pp
  52 The specified
  53 .Fa path
  54 must specify an existing file that is accessible to the calling process
  55 or the call will fail.
  56 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 LEGACY SYNOPSIS
  66 .Fd #include <sys/types.h>
  67 .Fd #include <sys/ipc.h>
  68 .Pp
  69 The include file
  70 .In sys/types.h
  71 is necessary.
  72 .Sh SEE ALSO
  73 .Xr semget 2 ,
  74 .Xr shmget 2 ,
  75 .Xr msgget 3 ,
  76 .Xr compat 5
  77 .Sh HISTORY
  78 The
  79 .Fn ftok
  80 function originates with System V and is typically used by programs
  81 that use the System V IPC routines.
  82 .Sh AUTHORS
  83 .An Thorsten Lockert Aq tholo@sigmasoft.com
  84 .Sh BUGS
  85 The returned key is computed based on the device minor number and inode
  86 of the specified
  87 .Fa path ,
  88 in combination with the lower 8 bits of the given
  89 .Fa id .
  90 Thus, it is quite possible for the routine to return duplicate keys.