tty_ioctl — ioctls for terminals and serial lines
#include <termios.h>
int
ioctl( |
int fd, |
| int cmd, | |
...); |
The ioctl(2) 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
nonportable programs. Use the POSIX interface described in
termios(3) whenever
possible.
argpEquivalent to tcgetattr(fd, argp).
Get the current serial port settings.
argpEquivalent to tcsetattr(fd, TCSANOW, argp).
Set the current serial port settings.
argpEquivalent to tcsetattr(fd, TCSADRAIN, argp).
Allow the output buffer to drain, and set the current serial port settings.
argpEquivalent to tcsetattr(fd, TCSAFLUSH, argp).
Allow the output buffer to drain, discard pending input, and set the current serial port settings.
The following four ioctls are just like TCGETS, TCSETS, TCSETSW, TCSETSF, except that they take a
struct termio *
instead of a struct termios
*.
TCGETA struct termio
*argp
TCSETA const struct
termio *argp
TCSETAW const struct
termio *argp
TCSETAF const struct
termio *argp
The termios structure of a
terminal can be locked. The lock is itself a termios structure, with nonzero bits or
fields indicating a locked value.
argpGets the locking status of the termios structure of the
terminal.
argpSets the locking status of the termios structure of the terminal.
Only a process with the CAP_SYS_ADMIN capability can do
this.
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
<sys/ioctl.h>
argpGet window size.
argpSet 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.
argEquivalent to 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 nonzero, nobody
knows what will happen.
(SVr4, UnixWare, Solaris, Linux treat tcsendbreak(fd,arg) with
nonzero arg like tcdrain(fd). SunOS treats
arg as a multiplier, and
sends a stream of bits arg
times as long as done for zero arg. DG/UX and AIX treat arg (when nonzero) as a time interval
measured in milliseconds. HP-UX ignores arg.)
argSo-called "POSIX version" of TCSBRK. It treats nonzero
arg as a timeinterval
measured in deciseconds, and does nothing when the
driver does not support breaks.
Turn break on, that is, start sending zero bits.
Turn break off, that is, stop sending zero bits.
argEquivalent to tcflow(fd, arg).
See tcflow(3) for the
argument values TCOOFF,
TCOON, TCIOFF, TCION.
argpGet the number of bytes in the input buffer.
argpSame as FIONREAD.
argpGet the number of bytes in the output buffer.
argEquivalent to tcflush(fd, arg).
See tcflush(3) for the
argument values TCIFLUSH,
TCOFLUSH, TCIOFLUSH.
Redirect output that would have gone to
/dev/console or
/dev/tty0 to the given
terminal. If that was a pseudoterminal 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 a process
with the CAP_SYS_ADMIN
capability may do this. If output was redirected
already EBUSY is
returned, but redirection can be stopped by using
this ioctl with fd pointing at
/dev/console or
/dev/tty0.
argMake 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. For this case, arg should be specified as
zero.
If this terminal is already the controlling
terminal of a different session group, then the ioctl
fails with EPERM,
unless the caller has the CAP_SYS_ADMIN capability and
arg equals 1, in which
case the terminal is stolen, and all processes that
had it as controlling terminal lose it.
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 SIGHUP and
SIGCONT to the
foreground process group and all processes in the
current session lose their controlling terminal.
argpWhen successful, equivalent to *argp = tcgetpgrp(fd).
Get the process group ID of the foreground process group on this terminal.
argpEquivalent to tcsetpgrp(fd, *argp).
Set the foreground process group ID of this terminal.
argpGet the session ID of the given terminal. This will fail with ENOTTY in case the terminal is not a master pseudoterminal and not our controlling terminal. Strange.
Put the terminal into exclusive mode. No further
open(2) operations
on the terminal are permitted. (They will fail with
EBUSY, except for a
process with the CAP_SYS_ADMIN capability.)
argpIf the terminal is currently in exclusive mode,
place a nonzero value in the location pointed to by
argp; otherwise, place
zero in *argp (since
Linux 3.8).
Disable exclusive mode.
argpGet the line discipline of the terminal.
argpSet the line discipline of the terminal.
argpEnable (when *argp
is nonzero) or disable packet mode. Can be applied to
the master side of a pseudoterminal only (and will
return ENOTTY
otherwise). In packet mode, each subsequent read(2) will return
a packet that either contains a single nonzero
control byte, or has a single byte containing zero
(' ') followed by data written on the slave side
of the pseudoterminal. 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 The start and stop characters are^S/^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.
argpReturn the current packet mode setting in the
integer pointed to by argp (since Linux 3.8).
argpSet (if *argp is
nonzero) or remove (if *argp is zero) the pseudoterminal
slave device. (See also unlockpt(3).)
argpPlace the current lock state of the pseudoterminal
slave device in the location pointed to by
argp (since Linux
3.8).
The BSD ioctls TIOCSTOP,
TIOCSTART, TIOCUCNTL, TIOCREMOTE have not been implemented
under Linux.
argpGet the status of modem bits.
argpSet the status of modem bits.
argpClear the indicated modem bits.
argpSet the indicated modem bits.
The following bits are used by the above 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)
argWait for any of the 4 modem bits (DCD, RI, DSR,
CTS) to change. The bits of interest are specified as
a bit mask in arg, by
ORing together any of the bit values, TIOCM_RNG, TIOCM_DSR, TIOCM_CD, and TIOCM_CTS. The caller should use
TIOCGICOUNT to see
which bit has changed.
argpGet counts of input serial line interrupts (DCD,
RI, DSR, CTS). The counts are written to the
serial_icounter_struct
structure pointed to by argp.
![]() |
Note |
|---|---|
|
Both 1->0 and 0->1 transitions are counted, except for RI, where only 0->1 transitions are counted. |
argp("Get software carrier flag") Get the status of
the CLOCAL flag in the c_cflag field of the
termios structure.
argp("Set software carrier flag") Set the CLOCAL flag
in the termios
structure when *argp is
nonzero, 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 terminal 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.
The ioctl(2) system call
returns 0 on success. On error, it returns −1 and sets
errno appropriately.
Invalid command parameter.
ENOIOCTLCMDUnknown command.
Inappropriate fd.
Insufficient permission.
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 set");
else
puts("TIOCM_DTR is not set");
close(fd);
}
This page is part of release 4.04 of the Linux man-pages project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
http://www.kernel.org/doc/man−pages/.
|
Copyright 2002 Walter Harms <walter.harmsinformatik.uni-oldenburg.de> and Andries Brouwer <aebcwi.nl>. %%%LICENSE_START(GPL_NOVERSION_ONELINE) Distributed under GPL %%%LICENSE_END |