path: root/man4/tty_ioctl.4

.\" Copyright 2002 Walter Harms <walter.harms@informatik.uni-oldenburg.de>
.\" and Andries Brouwer <aeb@cwi.nl>.
.\" Distributed under GPL.
.\"
.TH TTY_IOCTL 4 2008-10-29 "Linux" "Linux Programmer's Manual"
.SH NAME
tty_ioctl \- ioctls for terminals and serial lines
.SH SYNOPSIS
.B "#include <termios.h>"
.sp
.BI "int ioctl(int " fd ", int " cmd ", ...);"
.SH DESCRIPTION
The
.BR ioctl ()
call for terminals and serial ports accepts many possible command arguments.
Most require a third argument, of varying type, here called \fIargp\fP
or \fIarg\fP.
.LP
Use of
.I ioctl
makes for non-portable programs.
Use the POSIX interface described in
.BR termios (3)
whenever possible.
.SS "Get and Set Terminal Attributes"
.TP
.BI "TCGETS	struct termios *" argp
Equivalent to
.IR "tcgetattr(fd, argp)" .
.br
Get the current serial port settings.
.TP
.BI "TCSETS	const struct termios *" argp
Equivalent to
.IR "tcsetattr(fd, TCSANOW, argp)" .
.br
Set the current serial port settings.
.TP
.BI "TCSETSW	const struct termios *" argp
Equivalent to
.IR "tcsetattr(fd, TCSADRAIN, argp)" .
.br
Allow the output buffer to drain, and
set the current serial port settings.
.TP
.BI "TCSETSF	const struct termios *" argp
Equivalent to
.IR "tcsetattr(fd, TCSAFLUSH, argp)" .
.br
Allow the output buffer to drain, discard pending input, and
set the current serial port settings.
.LP
The following four ioctls are just like
.BR TCGETS ,
.BR TCSETS ,
.BR TCSETSW ,
.BR TCSETSF ,
except that they take a
.I "struct termio *"
instead of a
.IR "struct termios *" .
.TP
.BI "TCGETA	struct termio *" argp
.TP
.BI "TCSETA	const struct termio *" argp
.TP
.BI "TCSETAW	const struct termio *" argp
.TP
.BI "TCSETAF	const struct termio *" argp
.SS "Locking the termios structure"
The
.I termios
structure of a terminal can be locked.
The lock is itself a
.I termios
structure, with non-zero bits or fields indicating a
locked value.
.TP
.BI "TIOCGLCKTRMIOS	struct termios *" argp
Gets the locking status of the
.I termios
structure of the terminal.
.TP
.BI "TIOCSLCKTRMIOS	const struct termios *" argp
Sets the locking status of the
.I termios
structure of the terminal.
Only root (more precisely: a process with the
.BR CAP_SYS_ADMIN
capability) can do this.
.SS "Get and Set Window Size"
Window sizes are kept in the kernel, but not used by the kernel
(except in the case of virtual consoles, where the kernel will
update the window size when the size of the virtual console changes,
for example, by loading a new font).

The following constants and structure are defined in
.IR <sys/ioctl.h> .
.TP
.BI "TIOCGWINSZ	struct winsize *" argp
Get window size.
.TP
.BI "TIOCSWINSZ	const struct winsize *" argp
Set window size.
.LP
The struct used by these ioctls is defined as

.in +4n
.nf
struct winsize {
    unsigned short ws_row;
    unsigned short ws_col;
    unsigned short ws_xpixel;   /* unused */
    unsigned short ws_ypixel;   /* unused */
};
.fi
.in

When the window size changes, a
.B SIGWINCH
signal is sent to the
foreground process group.
.SS "Sending a Break"
.TP
.BI "TCSBRK	int " arg
Equivalent to
.IR "tcsendbreak(fd, arg)" .
.br
If the terminal is using asynchronous serial data transmission, and
.I arg
is zero, then send a break (a stream of zero bits) for between
0.25 and 0.5 seconds.
If the terminal is not using asynchronous
serial data transmission, then either a break is sent, or the function
returns without doing anything.
When
.I arg
is non-zero, nobody knows what will happen.

(SVr4, UnixWare, Solaris, Linux treat
.I "tcsendbreak(fd,arg)"
with non-zero
.I arg
like
.IR "tcdrain(fd)" .
SunOS treats
.I arg
as a multiplier, and sends a stream of bits
.I arg
times as long as done for zero
.IR arg .
DG/UX and AIX treat
.I arg
(when non-zero) as a time interval measured in milliseconds.
HP-UX ignores
.IR arg .)
.TP
.BI "TCSBRKP	int " arg
So-called "POSIX version" of
.BR TCSBRK .
It treats non-zero
.I arg
as a timeinterval measured in deciseconds, and does nothing
when the driver does not support breaks.
.TP
.B "TIOCSBRK	void"
Turn break on, that is, start sending zero bits.
.TP
.B "TIOCCBRK	void"
Turn break off, that is, stop sending zero bits.
.SS "Software flow control"
.TP
.BI "TCXONC	int " arg
Equivalent to
.IR "tcflow(fd, arg)" .
.br
See
.BR tcflow (3)
for the argument values
.BR TCOOFF ,
.BR TCOON ,
.BR TCIOFF ,
.BR TCION .
.SS "Buffer count and flushing"
.TP
.BI "FIONREAD	int *" argp
Get the number of bytes in the input buffer.
.TP
.BI "TIOCINQ	int *" argp
Same as
.BR FIONREAD .
.TP
.BI "TIOCOUTQ	int *" argp
Get the number of bytes in the output buffer.
.TP
.BI "TCFLSH	int " arg
Equivalent to
.IR "tcflush(fd, arg)" .
.br
See
.BR tcflush (3)
for the argument values
.BR TCIFLUSH ,
.BR TCOFLUSH ,
.BR TCIOFLUSH .
.SS "Faking input"
.TP
.BI "TIOCSTI	const char *" argp
Insert the given byte in the input queue.
.SS "Redirecting console output"
.TP
.B "TIOCCONS	void"
Redirect output that would have gone to
.I /dev/console
or
.I /dev/tty0
to the given terminal.
If that was a pseudo-terminal master, send it to the slave.
In Linux before version 2.6.10,
anybody can do this as long as the output was not redirected yet;
since version 2.6.10, only root (a process with the
.BR CAP_SYS_ADMIN
capability) may do this.
If output was redirected already
.B EBUSY
is returned,
but redirection can be stopped by using this ioctl with
.I fd
pointing at
.I /dev/console
or
.IR /dev/tty0 .
.SS "Controlling terminal"
.TP
.BI "TIOCSCTTY	int " arg
Make the given terminal the controlling terminal of the calling process.
The calling process must be a session leader and not have a
controlling terminal already.
If this terminal is already the controlling terminal
of a different session group then the ioctl fails with
.BR EPERM ,
unless the caller is root (more precisely: has the
.BR CAP_SYS_ADMIN
capability) and
.I arg
equals 1, in which case the terminal is stolen, and all processes that had
it as controlling terminal lose it.
.TP
.B TIOCNOTTY	void
If the given terminal was the controlling terminal of the calling process,
give up this controlling terminal.
If the process was session leader,
then send
.B SIGHUP
and
.B SIGCONT
to the foreground process group
and all processes in the current session lose their controlling terminal.
.SS "Process group and session ID"
.TP
.BI "TIOCGPGRP	pid_t *" argp
When successful, equivalent to
.IR "*argp = tcgetpgrp(fd)" .
.br
Get the process group ID of the foreground process group on this terminal.
.TP
.BI "TIOCSPGRP	const pid_t *" argp
Equivalent to
.IR "tcsetpgrp(fd, *argp)" .
.br
Set the foreground process group ID of this terminal.
.TP
.BI "TIOCGSID	pid_t *" argp
Get the session ID of the given terminal.
This will fail with
.B ENOTTY
in case the terminal is not a master pseudo-terminal
and not our controlling terminal.
Strange.
.SS "Exclusive mode"
.TP
.B "TIOCEXCL	void"
Put the terminal into exclusive mode.
No further
.BR open (2)
operations on the terminal are permitted.
(They will fail with
.BR EBUSY ,
except for root, that is, a process with the
.BR CAP_SYS_ADMIN
capability.)
.TP
.B "TIOCNXCL	void"
Disable exclusive mode.
.SS "Line discipline"
.TP
.BI "TIOCGETD	int *" argp
Get the line discipline of the terminal.
.TP
.BI "TIOCSETD	const int *" argp
Set the line discipline of the terminal.
.SS "Pseudo-terminal ioctls"
.TP
.BI "TIOCPKT	const int *" argp
Enable (when
.RI * argp
is non-zero) or disable packet mode.
Can be applied to the master side of a pseudo-terminal only (and will return
.B ENOTTY
otherwise).
In packet mode, each subsequent
.BR read (2)
will return a packet that either contains a single non-zero control byte,
or has a single byte containing zero (\(aq\0\(aq) followed by data
written on the slave side of the pseudo-terminal.
If the first byte is not
.B TIOCPKT_DATA
(0), it is an OR of one
or more of the following bits:

.nf
TIOCPKT_FLUSHREAD   The read queue for the terminal is flushed.
TIOCPKT_FLUSHWRITE  The write queue for the terminal is flushed.
TIOCPKT_STOP        Output to the terminal is stopped.
TIOCPKT_START       Output to the terminal is restarted.
TIOCPKT_DOSTOP      The start and stop characters are \fB^S\fP/\fB^Q\fP.
TIOCPKT_NOSTOP      The start and stop characters are not \fB^S\fP/\fB^Q\fP.
.fi

While this mode is in use, the presence
of control status information to be read
from the master side may be detected by a
.BR select (2)
for exceptional conditions.

This mode is used by
.BR rlogin (1)
and
.BR rlogind (8)
to implement a remote-echoed,
locally \fB^S\fP/\fB^Q\fP flow-controlled remote login.

The BSD ioctls
.BR TIOCSTOP ,
.BR TIOCSTART ,
.BR TIOCUCNTL ,
.B TIOCREMOTE
have not been implemented under Linux.
.SS "Modem control"
.TP
.BI "TIOCMGET	int *" argp
get the status of modem bits.
.TP
.BI "TIOCMSET	const int *" argp
set the status of modem bits.
.TP
.BI "TIOCMBIC	const int *" argp
clear the indicated modem bits.
.TP
.BI "TIOCMBIS	const int *" argp
set the indicated modem bits.
.LP
Bits used by these four ioctls:

.nf
TIOCM_LE        DSR (data set ready/line enable)
TIOCM_DTR       DTR (data terminal ready)
TIOCM_RTS       RTS (request to send)
TIOCM_ST        Secondary TXD (transmit)
TIOCM_SR        Secondary RXD (receive)
TIOCM_CTS       CTS (clear to send)
TIOCM_CAR       DCD (data carrier detect)
TIOCM_CD         see TIOCM_CAR
TIOCM_RNG       RNG (ring)
TIOCM_RI         see TIOCM_RNG
TIOCM_DSR       DSR (data set ready)
.fi
.SS "Marking a line as local"
.TP
.BI "TIOCGSOFTCAR	int *" argp
("Get software carrier flag")
Get the status of the CLOCAL flag in the c_cflag field of the
.I termios
structure.
.TP
.BI "TIOCSSOFTCAR	const int *" argp
("Set software carrier flag")
Set the CLOCAL flag in the
.I termios
structure when
.RI * argp
is non-zero, and clear it otherwise.
.LP
If the
.B CLOCAL
flag for a line is off, the hardware carrier detect (DCD)
signal is significant, and an
.BR open (2)
of the corresponding terminal will block until DCD is asserted,
unless the
.B O_NONBLOCK
flag is given.
If
.B CLOCAL
is set, the line behaves as if DCD is always asserted.
The software carrier flag is usually turned on for local devices,
and is off for lines with modems.
.SS "Linux-specific"
For the
.B TIOCLINUX
ioctl, see
.BR console_ioctl (4).
.SS "Kernel debugging"
.B "#include <linux/tty.h>"
.TP
.BI "TIOCTTYGSTRUCT	struct tty_struct *" argp
Get the
.I tty_struct
corresponding to
.IR fd .
.\"
.\" .SS "Serial info"
.\" .BR "#include <linux/serial.h>"
.\" .sp
.\" .TP
.\" .BI "TIOCGSERIAL	struct serial_struct *" argp
.\" Get serial info.
.\" .TP
.\" .BI "TIOCSSERIAL	const struct serial_struct *" argp
.\" Set serial info.
.SH "RETURN VALUE"
The
.BR ioctl ()
system call returns 0 on success.
On error it returns \-1 and sets
.I errno
appropriately.
.SH ERRORS
.TP
.B EINVAL
Invalid command parameter.
.TP
.B ENOIOCTLCMD
Unknown command.
.TP
.B ENOTTY
Inappropriate
.IR fd .
.TP
.B EPERM
Insufficient permission.
.SH EXAMPLE
Check the condition of DTR on the serial port.

.nf
#include <termios.h>
#include <fcntl.h>
#include <sys/ioctl.h>

int
main(void)
{
    int fd, serial;

    fd = open("/dev/ttyS0", O_RDONLY);
    ioctl(fd, TIOCMGET, &serial);
    if (serial & TIOCM_DTR)
        puts("TIOCM_DTR is not set");
    else
        puts("TIOCM_DTR is set");
    close(fd);
}
.fi
.SH "SEE ALSO"
.BR ioctl (2),
.BR termios (3),
.BR console_ioctl (4),
.BR pty (7)
.\"
.\" FIONBIO			const int *
.\" FIONCLEX			void
.\" FIOCLEX			void
.\" FIOASYNC			const int *
.\" from serial.c:
.\" TIOCSERCONFIG		void
.\" TIOCSERGWILD		int *
.\" TIOCSERSWILD		const int *
.\" TIOCSERGSTRUCT		struct async_struct *
.\" TIOCSERGETLSR		int *
.\" TIOCSERGETMULTI		struct serial_multiport_struct *
.\" TIOCSERSETMULTI		const struct serial_multiport_struct *
.\" TIOCGSERIAL, TIOCSSERIAL (see above)