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.\" $FreeBSD: release/9.1.0/lib/libc/stdlib/ptsname.3 240648 2012-09-18 13:13:28Z emaste $
.\"
.Dd August 20, 2008
.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 2 .
.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 2
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 ,
.Fn ptsname
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 2 ,
.Xr pts 4 ,
.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 2
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
.Fx 5.0 .