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.Dd February 5, 2022
.Dt UNLOCKPT 3C
.Os
.Sh NAME
.Nm unlockpt
.Nd unlock a pseudo-terminal device pair
.Sh SYNOPSIS
.In stdlib.h
.Ft int
.Fo unlockpt
.Fa "int fildes"
.Fc
.Sh DESCRIPTION
When a pseudo-terminal manager device is opened, whether through
.Xr posix_openpt 3C
or
.Xr open 2
on a
.Xr ptm 4D
device, the subsidiary device begins operation in a locked state.
The
.Fn unlockpt
function unlocks the pseudo-terminal subsidiary device associated with the
manager device to which
.Fa fildes
refers.
.Pp
Portable applications must call
.Fn unlockpt
before opening the pseudo-terminal subsidiary device.
.Sh RETURN VALUES
.Rv -std unlockpt
.Sh EXAMPLES
See
.Xr posix_openpt 3C
for an example that includes a call to
.Fn unlockpt .
.Sh ERRORS
The
.Fn unlockpt
function may fail if:
.Bl -tag -width Er
.It Er EBADF
The
.Fa fildes
argument is not a file descriptor open for writing.
.It Er EINVAL
EINVAL
The
.Fa fildes
argument is not associated with a pseudo-terminal manager device.
.El
.Sh INTERFACE STABILITY
.Sy Committed
.Sh MT LEVEL
.Sy Safe
.Sh SEE ALSO
.Xr open 2 ,
.Xr grantpt 3C ,
.Xr posix_openpt 3C ,
.Xr ptsname 3C ,
.Xr ptm 4D ,
.Xr attributes 7 ,
.Xr standards 7