.\"     $OpenBSD: posix_openpt.3,v 1.4 2019/01/25 00:19:25 millert Exp $
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.\" Copyright (c) 2012 Todd C. Miller <millert@openbsd.org>
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.Dd $Mdocdate: January 25 2019 $
.Dt POSIX_OPENPT 3
.Os
.Sh NAME
.Nm posix_openpt
.Nd open a pseudo-terminal device
.Sh SYNOPSIS
.In stdlib.h
.In fcntl.h
.Ft int
.Fn posix_openpt "int oflag"
.Sh DESCRIPTION
The
.Fn posix_openpt
function finds the next available pseudo-terminal and returns an open
file descriptor for its master device.
The path name of the slave device may be determined via the
.Fn ptsname
function.
Note that the
.Fn unlockpt
and
.Fn grantpt
functions should be called before opening the slave device.
.Pp
The
.Ar oflag
argument is formed by bitwise-inclusive
.Tn OR Ns 'ing
the following values defined in
.In fcntl.h :
.Bl -tag -width O_NOCTTY -offset indent
.It Dv O_RDWR
Open for reading and writing.
.It Dv O_NOCTTY
Prevent the device from being made the controlling terminal for the session.
This flag has no effect on
.Ox
and is included for compatibility with other systems.
.El
.Pp
The
.Dv O_RDWR
flag must be specified in
.Fa oflag .
If
.Fa oflag
contains values other than those listed above,
.Fn posix_openpt
will return an error.
.Sh RETURN VALUES
If successful,
.Fn posix_openpt
returns a non-negative integer, the file descriptor for the
pseudo-terminal master device.
Otherwise, a value of \-1 is returned and
.Va errno
is set to indicate the error.
.Sh ERRORS
The
.Fn posix_openpt
function will fail if:
.Bl -tag -width Er
.It Bq Er EMFILE
The per-process descriptor table is full.
.It Bq Er ENFILE
The system file table is full.
.It Bq Er EINVAL
The value of
.Fa oflag
is not valid.
.El
.Sh SEE ALSO
.Xr ptsname 3 ,
.Xr pty 4 ,
.Xr tty 4
.Sh STANDARDS
The
.Fn posix_openpt
function conforms to
.St -p1003.1-2001 .
.Sh HISTORY
The
.Fn posix_openpt
function appeared in
.Ox 5.3 .