.\"
.\" Copyright (c) 2002 The FreeBSD Project, Inc.
.\" All rights reserved.
.\"
.\" This software includes code contributed to the FreeBSD Project
.\" by Ryan Younce of North Carolina State University.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. Neither the name of the FreeBSD Project nor the names of its
.\"    contributors may be used to endorse or promote products derived from
.\"    this software without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE FREEBSD PROJECT AND CONTRIBUTORS
.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
.\" LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
.\" PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FREEBSD PROJECT
.\" OR ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
.\" TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
.\" PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
.\" LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
.\" NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
.\" SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.\" $FreeBSD: src/lib/libc/stdlib/ptsname.3,v 1.4 2010/04/14 19:08:06 uqs Exp $
.\"
.Dd September 10, 2009
.Dt PTSNAME 3
.Os
.Sh NAME
.Nm grantpt ,
.Nm ptsname ,
.Nm unlockpt
.Nd pseudo-terminal access functions
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In stdlib.h
.Ft int
.Fn grantpt "int fildes"
.Ft "char *"
.Fn ptsname "int fildes"
.Ft int
.Fn unlockpt "int fildes"
.Sh DESCRIPTION
The
.Fn grantpt ,
.Fn ptsname ,
and
.Fn unlockpt
functions allow access to pseudo-terminal devices.
These three functions accept a file descriptor that references the
master half of a pseudo-terminal pair.
This file descriptor is created with
.Xr posix_openpt 3
or by calling
.Xr open 2
on
.Pa /dev/ptmx .
.Pp
The
.Fn grantpt
function is used to establish ownership and permissions
of the slave device counterpart to the master device
specified with
.Fa fildes .
The slave device's ownership is set to the real user ID
of the calling process, and the permissions are set to
user readable-writable and group writable.
The group owner of the slave device is also set to the
group
.Dq Li tty .
.Pp
The
.Fn ptsname
function returns the full pathname of the slave device
counterpart to the master device specified with
.Fa fildes .
This value can be used
to subsequently open the appropriate slave after
.Xr posix_openpt 3
and
.Fn grantpt
have been called.
.Pp
The
.Fn unlockpt
function clears the lock held on the pseudo-terminal pair
for the master device specified with
.Fa fildes .
.Sh RETURN VALUES
.Rv -std grantpt unlockpt
.Pp
The
.Fn ptsname
function returns a pointer to the name
of the slave device on success; otherwise a
.Dv NULL
pointer is returned.
.Sh ERRORS
The
.Fn grantpt
and
.Fn unlockpt
functions may fail and set
.Va errno
to:
.Bl -tag -width Er
.It Bq Er EBADF
.Fa fildes
is not a valid open file descriptor.
.It Bq Er EINVAL
.Fa fildes
is not a master pseudo-terminal device.
.El
.Pp
In addition, the
.Fn grantpt
function may set
.Va errno
to:
.Bl -tag -width Er
.It Bq Er EACCES
The slave pseudo-terminal device could not be accessed.
.El
.Sh SEE ALSO
.Xr posix_openpt 3 ,
.Xr tty 4
.Sh STANDARDS
The
.Fn ptsname
function conforms to
.St -p1003.1-2008 .
.Pp
This implementation of
.Fn grantpt
and
.Fn unlockpt
does not conform to
.St -p1003.1-2008 ,
because it depends on
.Xr posix_openpt 3
to create the pseudo-terminal device with proper permissions in place.
It only validates whether
.Fa fildes
is a valid pseudo-terminal master device.
Future revisions of the specification will likely allow this behaviour,
as stated by the Austin Group.
.Sh HISTORY
The
.Fn grantpt ,
.Fn ptsname
and
.Fn unlockpt
functions appeared in
.Dx 2.3 .