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.\" Converted into a manpage again by Martin Schulze <joey@infodrom.org>
.\"
.\" Added -lutil remark, 030718
.\"
.TH OPENPTY 3 2017-09-15 "GNU" "Linux Programmer's Manual"
.SH NAME
openpty, login_tty, forkpty \- terminal utility functions
.SH SYNOPSIS
.nf
.B #include <pty.h>
.PP
.BI "int openpty(int *" fd_pty ", int *" fd_tty ", char *" name ,
.BI " const struct termios *" termp ,
.BI " const struct winsize *" winp );
.PP
.BI "pid_t forkpty(int *" fd_pty ", char *" name ,
.BI " const struct termios *" termp ,
.BI " const struct winsize *" winp );
.B #include <utmp.h>
.PP
.BI "int login_tty(int " fd );
.PP
Link with \fI\-lutil\fP.
.fi
.SH DESCRIPTION
The
.BR openpty ()
function finds an available pseudoterminal device pair
and returns file descriptors
for the pseudoterminal device and the corresponding terminal device in
.I fd_pty
and
.IR fd_tty .
If
.I name
is not NULL, the filename of the corresponding terminal device is returned in
.IR name .
If
.I termp
is not NULL, the terminal parameters of the corresponding terminal device
will be set to the
values in
.IR termp .
If
.I winp
is not NULL, the window size of the corresponding terminal device
will be set to the values in
.IR winp .
.PP
The
.BR login_tty ()
function prepares for a login on the terminal
referred to by the file descriptor
.I fd
(which may be a real terminal device,
or the terminal end of a pseudoterminal device pair as
returned by
.BR openpty ())
by creating a new session, making
.I fd
the controlling terminal for the calling process, setting
.I fd
to be the standard input, output, and error streams of the current
process, and closing
.IR fd .
.PP
The
.BR forkpty ()
function combines
.BR openpty (),
.BR fork (2),
and
.BR login_tty ()
to create a new process operating in a pseudoterminal.
A file descriptor referring to
the pseudoterminal end of the pseudoterminal device pair
is returned in
.IR fd_pty .
If
.I name
is not NULL, the buffer it points to is used to return the
filename of the corresponding terminal device.
The
.I termp
and
.I winp
arguments, if not NULL,
will determine the terminal attributes and window size of the terminal end
of the pseudoterminal device pair.
.SH RETURN VALUE
If a call to
.BR openpty (),
.BR login_tty (),
or
.BR forkpty ()
is not successful, \-1 is returned and
.I errno
is set to indicate the error.
Otherwise,
.BR openpty (),
.BR login_tty (),
and the child process of
.BR forkpty ()
return 0, and the parent process of
.BR forkpty ()
returns the process ID of the child process.
.SH ERRORS
.BR openpty ()
fails if:
.TP
.B ENOENT
There are no available terminals.
.PP
.BR login_tty ()
fails if
.BR ioctl (2)
fails to set
.I fd
to the controlling terminal of the calling process.
.PP
.BR forkpty ()
fails if either
.BR openpty ()
or
.BR fork (2)
fails.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbw20 lb lb
l l l.
Interface Attribute Value
T{
.BR forkpty (),
.BR openpty ()
T} Thread safety MT-Safe locale
T{
.BR login_tty ()
T} Thread safety MT-Unsafe race:ttyname
.TE
.sp 1
.SH CONFORMING TO
These are BSD functions, present in glibc.
They are not standardized in POSIX.
.SH NOTES
The
.B const
modifiers were added to the structure pointer arguments of
.BR openpty ()
and
.BR forkpty ()
in glibc 2.8.
.PP
In versions of glibc before 2.0.92,
.BR openpty ()
returns file descriptors for a BSD pseudoterminal pair;
since glibc 2.0.92,
it first attempts to open a UNIX 98 pseudoterminal pair,
and falls back to opening a BSD pseudoterminal pair if that fails.
.SH BUGS
Nobody knows how much space should be reserved for
.IR name .
So, calling
.BR openpty ()
or
.BR forkpty ()
with non-NULL
.I name
may not be secure.
.SH SEE ALSO
.BR fork (2),
.BR ttyname (3),
.BR pty (7)