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  48 .Dd February 5, 2022
  49 .Dt UNLOCKPT 3C
  50 .Os
  51 .Sh NAME
  52 .Nm unlockpt
  53 .Nd unlock a pseudo-terminal device pair
  54 .Sh SYNOPSIS
  55 .In stdlib.h
  56 .Ft int
  57 .Fo unlockpt
  58 .Fa "int fildes"
  59 .Fc
  60 .Sh DESCRIPTION
  61 When a pseudo-terminal manager device is opened, whether through
  62 .Xr posix_openpt 3C
  63 or
  64 .Xr open 2
  65 on a
  66 .Xr ptm 7D
  67 device, the subsidiary device begins operation in a locked state.
  68 The
  69 .Fn unlockpt
  70 function unlocks the pseudo-terminal subsidiary device associated with the
  71 manager device to which
  72 .Fa fildes
  73 refers.
  74 .Pp
  75 Portable applications must call
  76 .Fn unlockpt
  77 before opening the pseudo-terminal subsidiary device.
  78 .Sh RETURN VALUES
  79 .Rv -std unlockpt
  80 .Sh EXAMPLES
  81 See
  82 .Xr posix_openpt 3C
  83 for an example that includes a call to
  84 .Fn unlockpt .
  85 .Sh ERRORS
  86 The
  87 .Fn unlockpt
  88 function may fail if:
  89 .Bl -tag -width Er
  90 .It Er EBADF
  91 The
  92 .Fa fildes
  93 argument is not a file descriptor open for writing.
  94 .It Er EINVAL
  95 EINVAL
  96 The
  97 .Fa fildes
  98 argument is not associated with a pseudo-terminal manager device.
  99 .El
 100 .Sh INTERFACE STABILITY
 101 .Sy Committed
 102 .Sh MT LEVEL
 103 .Sy Safe
 104 .Sh SEE ALSO
 105 .Xr open 2 ,
 106 .Xr grantpt 3C ,
 107 .Xr posix_openpt 3C ,
 108 .Xr ptsname 3C ,
 109 .Xr attributes 5 ,
 110 .Xr standards 5 ,
 111 .Xr ptm 7D