man-pages/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  2003-07-18 "GNU" "Linux Programmer's Manual"
.SH NAME
openpty, login_tty, forkpty \- tty utility functions
.SH SYNOPSIS
.nf
.B #include <pty.h>
.sp
.BI "int openpty(int *" amaster ", int *" aslave ", char *" name ,
.BI "            struct termios *" termp ", struct winsize *" winp );
.sp
.BI "pid_t forkpty(int *" amaster ", char *" name ", struct termios *" termp ,
.BI "              struct winsize *" winp );
.sp
.B #include <utmp.h>
.sp
.BI "int login_tty(int " fd );
.sp
Link with \fI\-lutil\fP.
.fi
.SH DESCRIPTION
The
.BR openpty ()
function finds an available pseudo-terminal 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 .

The
.BR login_tty ()
function prepares for a login on the tty
.I fd
(which may be a real tty device, or the slave of a pseudo-terminal 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 .

The
.BR forkpty ()
function combines
.BR openpty (),
.BR fork (2),
and
.BR login_tty ()
to create a new process operating in a pseudo-terminal.
The file
descriptor of the master side of the pseudo-terminal is returned in
.IR amaster ,
and the filename of the slave in
.I name
if it is not NULL.
The
.I termp
and
.I winp
arguments, if not NULL,
will determine the terminal attributes and window size of the slave
side of the pseudo-terminal.
.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 ()
will fail if:
.TP
.B ENOENT
There are no available ttys.
.LP
.BR login_tty ()
will fail if
.BR ioctl (2)
fails to set
.I fd
to the controlling terminal of the calling process.
.LP
.BR forkpty ()
will fail if either
.BR openpty ()
or
.BR fork (2)
fails.
.SH "CONFORMING TO"
These are BSD functions, present in libc5 and glibc2.
.SH NOTES
.\" These functions are included in libutil, hence you'll need to add
.\" .B \-lutil
.\" to your compiler command line.
.\"
In versions of glibc before 2.0.92,
.BR openpty ()
returns file descriptors for a BSD pseudo-terminal pair;
since glibc 2.0.92,
it first attempts to open a Unix 98 pseudo-terminal pair,
and falls back to opening a BSD pseudo-terminal 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)