man3/openpty.3

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.\" Converted into a manpage again by Martin Schulze <joey@infodrom.org>
.\"
.\" Added -lutil remark, 030718
.\"
.TH OPENPTY 3  2021-03-22 "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 *" amaster ", int *" aslave ", char *" name ,
.BI "              const struct termios *" termp ,
.BI "              const struct winsize *" winp );
.BI "pid_t forkpty(int *" amaster ", char *" name ,
.BI "              const struct termios *" termp ,
.BI "              const struct winsize *" winp );
.PP
.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 and returns file descriptors
for the master and slave in
.I amaster
and
.IR aslave .
If
.I name
is not NULL, the filename of the slave is returned in
.IR name .
If
.I termp
is not NULL, the terminal parameters of the slave will be set to the
values in
.IR termp .
If
.I winp
is not NULL, the window size of the slave 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 slave of a pseudoterminal 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
master side of the pseudoterminal is returned in
.IR amaster .
If
.I name
is not NULL, the buffer it points to is used to return the
filename of the slave.
The
.I termp
and
.I winp
arguments, if not NULL,
will determine the terminal attributes and window size of the slave
side of the pseudoterminal.
.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).
.ad l
.nh
.TS
allbox;
lbx 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
.hy
.ad
.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)