- NAME
- SYNOPSIS
- DESCRIPTION
- Get and Set Terminal Attributes
- Locking the termios structure
- Get and Set Window Size
- Sending a Break
- Software flow control
- Buffer count and flushing
- Faking input
- Redirecting console output
- Controlling tty
- Process group and session ID
- Exclusive mode
- Line discipline
- Pseudo-tty ioctls
- Modem control
- Marking a line as local
- Linux specific
- Kernel debugging
- RETURN VALUE
- ERRORS
- EXAMPLE
- SEE ALSO
tty_ioctl
NAME
tty ioctl - ioctls for terminals and serial lines
SYNOPSIS
R #include <termios.h>
I int ioctl(int fd , int cmd , ...);
DESCRIPTION
The
R ioctl ()
call for terminals and serial ports accepts many possible command arguments.
Most require a third argument, of varying type, here called argp
or arg.
Use of
ioctl
makes for non-portable programs.
Use the POSIX interface described in
termios(3)
whenever possible.
Get and Set Terminal Attributes
I TCGETS struct termios * argp
Equivalent to
R tcgetattr(fd, argp) .
Get the current serial port settings.
Get the current serial port settings.
I TCSETS const struct termios * argp
Equivalent to
R tcsetattr(fd, TCSANOW, argp) .
Set the current serial port settings.
Set the current serial port settings.
I TCSETSW const struct termios * argp
Equivalent to
R tcsetattr(fd, TCSADRAIN, argp) .
Allow the output buffer to drain, and set the current serial port settings.
Allow the output buffer to drain, and set the current serial port settings.
I TCSETSF const struct termios * argp
Equivalent to
R tcsetattr(fd, TCSAFLUSH, argp) .
Allow the output buffer to drain, discard pending input, and set the current serial port settings.
Allow the output buffer to drain, discard pending input, and set the current serial port settings.
The following four ioctls are just like
R TCGETS ,
R TCSETS ,
R TCSETSW ,
R TCSETSF ,
except that they take a
struct termio *
instead of a
R struct termios * .
I TCGETA struct termio * argp
I TCSETA const struct termio * argp
I TCSETAW const struct termio * argp
I TCSETAF const struct termio * argp
I TIOCGLCKTRMIOS struct termios * argp
Gets the locking status of the termios structure of
the terminal.
I TIOCSLCKTRMIOS const struct termios * argp
Sets the locking status of the termios structure of
the terminal.
Only root can do this.
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).I TIOCGWINSZ struct winsize * argp
Get window size.
I TIOCSWINSZ const struct winsize * argp
Set window size.
The struct used by these ioctls is defined as
struct winsize {
unsigned short ws_row;
unsigned short ws_col;
unsigned short ws_xpixel; /* unused */
unsigned short ws_ypixel; /* unused */
};
When the window size changes, a
SIGWINCH
signal is sent to the
foreground process group.
Sending a Break
I TCSBRK int arg
Equivalent to
R tcsendbreak(fd, arg) .
If the terminal is using asynchronous serial data transmission, and 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 arg is non-zero, nobody knows what will happen. (SVr4, UnixWare, Solaris, Linux treat tcsendbreak(fd,arg) with non-zero arg like R tcdrain(fd) . SunOS treats arg as a multiplier, and sends a stream of bits arg times as long as done for zero R arg . DG/UX and AIX treat arg (when non-zero) as a timeinterval measured in milliseconds. HP-UX ignores R arg .)
If the terminal is using asynchronous serial data transmission, and 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 arg is non-zero, nobody knows what will happen. (SVr4, UnixWare, Solaris, Linux treat tcsendbreak(fd,arg) with non-zero arg like R tcdrain(fd) . SunOS treats arg as a multiplier, and sends a stream of bits arg times as long as done for zero R arg . DG/UX and AIX treat arg (when non-zero) as a timeinterval measured in milliseconds. HP-UX ignores R arg .)
I TCSBRKP int arg
So-called "POSIX version" of
R TCSBRK .
It treats non-zero
arg
as a timeinterval measured in deciseconds, and does nothing
when the driver does not support breaks.
I TIOCSBRK void
Turn break on, that is, start sending zero bits.
I TCXONC int arg
Equivalent to
R tcflow(fd, arg) .
See tcflow(3) for the argument values R TCOOFF , R TCOON , R TCIOFF , R TCION .
See tcflow(3) for the argument values R TCOOFF , R TCOON , R TCIOFF , R TCION .
Buffer count and flushing
I FIONREAD int * argp
Get the number of bytes in the input buffer.
I TIOCINQ int * argp
Same as
R FIONREAD .
I TIOCOUTQ int * argp
Get the number of bytes in the output buffer.
I TCFLSH int arg
Equivalent to
R tcflush(fd, arg) .
See tcflush(3) for the argument values R TCIFLUSH , R TCOFLUSH , R TCIOFLUSH .
See tcflush(3) for the argument values R TCIFLUSH , R TCOFLUSH , R TCIOFLUSH .
Faking input
I TIOCCONS void
Redirect output that would have gone to
/dev/console
or
/dev/tty0
to the given tty.
If that was a pty master, send it to the slave.
Anybody can do this as long as the output was not redirected yet.
If it was redirected already
EBUSY
is returned,
but root may stop redirection by using this ioctl with
fd
pointing at
/dev/console
or
R /dev/tty0 .
Controlling tty
I TIOCSCTTY int arg
Make the given tty the controlling tty of the current process.
The current process must be a session leader and not have a
controlling tty already.
If this tty is already the controlling tty
of a different session group then the ioctl fails with
R EPERM ,
unless the caller is root and
arg
equals 1, in which case the tty is stolen, and all processes that had
it as controlling tty lose it.
I TIOCNOTTY void
I TIOCGPGRP pid_t * argp
When successful, equivalent to
R *argp = tcgetpgrp(fd) .
Get the process group ID of the foreground process group on this tty.
Get the process group ID of the foreground process group on this tty.
I TIOCSPGRP const pid_t * argp
Equivalent to
R tcsetpgrp(fd, *argp) .
Set the foreground process group ID of this tty.
Set the foreground process group ID of this tty.
I TIOCGSID pid_t * argp
I TIOCEXCL void
Put the tty into exclusive mode.
No further
open(2)
operations on the terminal are permitted.
(They will fail with
R EBUSY ,
except for root.)
I TIOCGETD int * argp
Get the line discipline of the tty.
I TIOCPKT const int * argp
Enable (when
*argp
is non-zero) or disable packet mode.
Can be applied to the master side of a pseudo-terminal only (and will return
ENOTTY
otherwise).
In packet mode, each subsequent
read(2)
will return a packet that either contains a single non-zero control byte,
or has a single byte containing zero (''\0') followed by data
written on the slave side of the pty.
If the first byte is not
TIOCPKT_DATA
(0), it is an OR of one
or more of the following bits:
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 t_stopc is `^S' and t_startc is `^Q'. TIOCPKT_NOSTOP the start and stop characters are not `^S/^Q'.While this mode is in use, the presence of control status information to be read from the master side may be detected by a select(2) for exceptional conditions. This mode is used by rlogin(1) and rlogind(8) to implement a remote-echoed, locally `^S/^Q' flow-controlled remote login. The BSD ioctls R TIOCSTOP , R TIOCSTART , R TIOCUCNTL , R TIOCREMOTE have not been implemented under Linux.
Modem control
I TIOCMGET int * argp
get the status of modem bits.
I TIOCMSET const int * argp
set the status of modem bits.
I TIOCMBIC const int * argp
clear the indicated modem bits.
I TIOCMBIS const int * argp
set the indicated modem bits.
Bits used by these four ioctls:
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)
Marking a line as local
I TIOCGSOFTCAR int * argp
("Get software carrier flag")
Get the status of the CLOCAL flag in the c_cflag field of the
termios structure.
I TIOCSSOFTCAR const int * argp
("Set software carrier flag")
Set the CLOCAL flag in the termios structure when
*argp
is non-zero, and clear it otherwise.
If the
CLOCAL
flag for a line is off, the hardware carrier detect (DCD)
signal is significant, and an
open(2)
of the corresponding tty will block until DCD is asserted,
unless the
O_NONBLOCK
flag is given.
If
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.
Linux specific
For the TIOCLINUX ioctl, see console_ioctl(4).Kernel debugging
R #include <linux/tty.h>I TIOCTTYGSTRUCT struct tty_struct * argp
Get the tty_struct corresponding to
R fd .
RETURN VALUE
The
R ioctl ()
system call returns 0 on success.
On error it returns -1 and sets
errno
appropriately.
ERRORS
ENOIOCTLCMD
Unknown command.
EINVAL
Invalid command parameter.
EPERM
Insufficient permission.
ENOTTY
Inappropriate
R fd .
EXAMPLE
Check the condition of DTR on the serial port.
#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);
}
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