gen.subproj/ftok.3

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   3 .\" Copyright (c) 1994 SigmaSoft, Th. Lockert <tholo@sigmasoft.com>
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  28 .Dd June 24, 1994
  29 .Dt FTOK 3
  30 .Os
  31 .Sh NAME
  32 .Nm ftok
  33 .Nd create IPC indentifier from a pathname
  34 .Sh SYNOPSIS
  35 .Fd #include <sys/types.h>
  36 .Fd #include <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 2 ,
  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 refer to an existing file that is accessible to the calling process
  55 or the call will fail.  Also, note that links to files will return the
  56 same key, given the same
  57 .Fa id .
  58 Only the 8 least significant bits of
  59 .Fa id
  60 are used in the key generation; the rest of the bits are ignored.
  61 .Sh RETURN VALUES
  62 The
  63 .Fn ftok
  64 function will return (key_t)\-1 if
  65 .Fa path
  66 does not exist or if it cannot be accessed by the calling process.
  67 .Sh SEE ALSO
  68 .Xr msgget 2 ,
  69 .Xr semget 2 ,
  70 .Xr shmget 2
  71 .Sh HISTORY
  72 The
  73 .Fn ftok
  74 function originated with System V and is typically used by programs
  75 that use the System V IPC routines.
  76 .Sh AUTHOR
  77 Thorsten Lockert <tholo@sigmasoft.com>
  78 .Sh BUGS
  79 The returned key is computed based on the device and inode of the
  80 specified
  81 .Fa path
  82 in combination with the given
  83 .Fa id .
  84 Thus it is quite possible for the routine to return duplicate keys
  85 given that those fields are not 8- and 16-bit quantities like they
  86 were on System V based systems where this library routine's ancestors
  87 were originally created.