.\"	$NetBSD: openpty.3,v 1.17 2012/07/27 21:33:46 christos Exp $
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.Dd July 27, 2012
.Dt OPENPTY 3
.Os
.Sh NAME
.Nm openpty ,
.Nm login_tty ,
.Nm forkpty
.Nd tty utility functions
.Sh LIBRARY
.Lb libutil
.Sh SYNOPSIS
.In util.h
.Ft int
.Fn openpty "int *amaster" "int *aslave" "char *name" "struct termios *termp" "struct winsize *winp"
.Ft int
.Fn login_tty "int fd"
.Ft pid_t
.Fn forkpty "int *amaster" "char *name" "struct termios *termp" "struct winsize *winp"
.Sh DESCRIPTION
The
.Fn openpty ,
.Fn login_tty ,
and
.Fn forkpty
functions perform manipulations on ttys and pseudo-ttys.
.Pp
The
.Fn openpty
function finds an available pseudo-tty and returns file descriptors
for the master and slave in
.Fa amaster
and
.Fa aslave .
If
.Fa name
is non-null, the filename of the slave is returned in
.Fa name .
The length of
.Fa name
is limited to
.Dv PATH_MAX
as any other regular path name, so a buffer of this size should be used.
.\" .Dv 16
.\" characters in the current
.\" .Xr ptm 4
.\" device driver (including the terminating
.\" .Dv NUL )
.\" which limits the maximum to
.\" .Dv 100,000
.\" ptys.
If
.Fa termp
is non-null, the terminal parameters of the slave will be set to the
values in
.Fa termp .
If
.Fa winp
is non-null, the window size of the slave will be set to the values in
.Fa winp .
.Pp
The
.Fn login_tty
function prepares for a login on the tty
.Fa fd
(which may be a real tty device, or the slave of a pseudo-tty as
returned by
.Fn openpty )
by creating a new session, making
.Fa fd
the controlling terminal for the current process, setting
.Fa fd
to be the standard input, output, and error streams of the current
process, and closing
.Fa fd .
.Pp
The
.Fn forkpty
function combines
.Fn openpty ,
.Fn fork ,
and
.Fn login_tty
to create a new process operating in a pseudo-tty.
The file descriptor of the master side of the pseudo-tty is returned
(to the parent process only) in
.Fa amaster .
The filename of the slave is returned (to both the parent and child
processes) in
.Fa name
if
.Fa name
is non-null.
The
.Fa termp
and
.Fa winp
parameters, if non-null, will determine the terminal attributes and
window size of the slave side of the pseudo-tty.
.Sh RETURN VALUES
If a call to
.Fn openpty ,
.Fn login_tty ,
or
.Fn forkpty
is not successful, -1 is returned and
.Va errno
is set to indicate the error.
Otherwise,
.Fn openpty ,
.Fn login_tty ,
and the child process of
.Fn forkpty
return 0, and the parent process of
.Fn forkpty
returns the process ID of the child process.
.Sh FILES
.Bl -tag -width /dev/[pt]ty[p-zP-T][0-9a-zA-Z] -compact
.It Pa /dev/[pt]ty[p-zP-T][0-9a-zA-Z]
.El
.Sh ERRORS
.Fn openpty
will fail if:
.Bl -tag -width Er
.It Bq Er ENOENT
There are no available ttys.
.It Bq Er EPERM
The caller was not the superuser and the
.Xr ptm 4
device is missing or not configured.
.El
.Pp
.Fn login_tty
will fail if
.Fn ioctl
fails to set
.Fa fd
to the controlling terminal of the current process.
.Fn forkpty
will fail if either
.Fn openpty
or
.Fn fork
fails.
.Sh SEE ALSO
.Xr fork 2