termios(2)

general terminal interface

From the original Amiga UNIX 2.1 manual. Some things it mentions may not be in this release.

Also by this name: tcsetpgrp(3C), C library

NAME · SYNOPSIS · DESCRIPTION · DIAGNOSTICS · SEE ALSO

NAME

termios: tcgetattr, tcsetattr, tcsendbreak, tcdrain, tcflush, tcflow, cfgetospeed, cfgetispeed, cfsetispeed, cfsetospeed, tcgetpgrp, tcsetpgrp, tcgetsid - general terminal interface

SYNOPSIS

#include <termios.h>

int tcgetattr(int fildes, struct termios *termios_p);
int tcsetattr(int fildes, int optional_actions,
     const struct termios *termios_p);

int tcsendbreak(int fildes, int duration);
int tcdrain(int fildes);

int tcflush(int fildes, int queue_selector);
int tcflow(int fildes, int action);

speed_t cfgetospeed(struct termios *termios_p);
int cfsetospeed(const struct termios *termios_p, speed_t speed);

speed_t cfgetispeed(struct termios *termios_p);
int cfsetispeed(const struct termios *termios_p, speed_t speed);

#include <sys/types.h>
#include <termios.h>
pid_t tcgetpgrp(int fildes);

int tcsetpgrp(int fildes, pid_t pgid);
pid_t tcgetsid(int fildes);

DESCRIPTION

These functions describe a general terminal interface for controlling asynchronous communications ports. A more detailed overview of the terminal interface can be found in termio(7), which also describes an ioctl(2) interface that provides the same functionality. However, the function interface described here is the preferred user interface.

Many of the functions described here have a termios_p argument that is a pointer to a termios structure. This structure contains the following members:

tcflag_t   c_iflag;        /* input modes */
tcflag_t   c_oflag;        /* output modes */
tcflag_t   c_cflag;        /* control modes */
tcflag_t   c_lflag;        /* local modes */
cc_t       c_cc[NCCS];     /* control chars */

These structure members are described in detail in termio(7).

Get and Set Terminal Attributes

The tcgetattr function gets the parameters associated with the object referred by fildes and stores them in the termios structure referenced by termios_p. This function may be invoked from a background process; however, the terminal attributes may be subsequently changed by a foreground process.

The tcsetattr function sets the parameters  associated  with
the terminal (unless support is required from the underlying
hardware that is not available) from the  termios  structure
referenced by termios_p as follows:
     If  optional_actions  is  TCSANOW,  the  change  occurs
     immediately.   If  optional_actions  is  TCSADRAIN, the
     change occurs after all output written  to  fildes  has
     been  transmitted.   This  function should be used when
     changing   parameters   that   affect    output.     If
     optional_actions  is TCSAFLUSH, the change occurs after
     all output written to the object referred by fildes has
     been  transmitted, and all input that has been received
     but not read is discarded before the change is made.

The symbolic constants for the values of optional_actions are defined in <termios.h>.

Line Control

If the terminal is using asynchronous serial data transmission, the tcsendbreak function causes transmission of a continuous stream of zero-valued bits for a specific duration. If duration is zero, it causes transmission of zero-valued bits for at least 0.25 seconds, and not more than 0.5 seconds. If duration is not zero, it behaves in a way similar to tcdrain.

If the terminal is not using asynchronous serial data transmission, the tcsendbreak function sends data to generate a break condition or returns without taking any action.

The tcdrain function waits until all output written to the object referred to by fildes has been transmitted.

The tcflush function discards data  written  to  the  object
referred  to by fildes but not transmitted, or data received
but not read, depending on the value of queue_selector:
     If queue_selector is TCIFLUSH, it flushes data received
     but  not  read.   If  queue_selector  is  TCOFLUSH,  it
     flushes  data  written   but   not   transmitted.    If
     queue_selector  is  TCIOFLUSH,  it  flushes  both  data
     received  but  not  read,  and  data  written  but  not
     transmitted.

The tcflow function suspends transmission  or  reception  of
data  on  the object referred to by fildes, depending on the
value of action:
     If action is TCOOFF, it suspends output.  If action  is
     TCOON, it restarts suspended output.  If action if TCI-
     OFF, the  system  transmits  a  STOP  character,  which
     causes the terminal device to stop transmitting data to
     the system.  If action is TCION, the system transmits a
     START  character,  which  causes the terminal device to
     start transmitting data to the system.

Get and Set Baud Rate

The baud rate functions get and set the values of the input and output baud rates in the termios structure. The effects on the terminal device described below do not become effective until the tcsetattr function is successfully called.

The input and output baud rates are stored  in  the  termios
structure.   The  values  shown  in the table are supported.
The names in this table are defined in <termios.h>.
        Name   Description       Name    Description
        ____________________________________________
        B0         Hang up      B600        600 baud
        B50        50 baud      B1200      1200 baud
        B75        75 baud      B1800      1800 baud
        B110      110 baud      B2400      2400 baud
        B134    134.5 baud      B4800      4800 baud
        B150      150 baud      B9600      9600 baud
        B200      200 baud      B19200    19200 baud
        B300      300 baud      B38400    38400 baud

cfgetospeed gets the output baud rate and stores it in the termios structure pointed to by termios_p.

cfsetospeed sets the output baud rate stored in the termios structure pointed to by termios_p to speed. The zero baud rate, B0, is used to terminate the connection. If B0 is specified, the modem control lines are no longer be asserted. Normally, this disconnects the line.

cfgetispeed gets the input baud rate and stores it in the termios structure pointed to by termios_p.

cfsetispeed sets the input baud rate stored in the termios structure pointed to by termios_p to speed. If the input baud rate is set to zero, the input baud rate is specified by the value of the output baud rate. Both cfsetispeed and cfsetospeed return a value of zero if successful and -1 to indicate an error. Attempts to set unsupported baud rates are ignored. This refers both to changes to baud rates not supported by the hardware, and to changes setting the input and output baud rates to different values if the hardware does not support this.

Get and Set Terminal Foreground Process Group ID

tcsetpgrp sets the foreground process group ID of the terminal specified by fildes to pgid. The file associated with fildes must be the controlling terminal of the calling process and the controlling terminal must be currently associated with the session of the calling process. pgid must match a process group ID of a process in the same session as the calling process.

tcgetpgrp returns the foreground process group ID of the terminal specified by fildes. tcgetpgrp is allowed from a process that is a member of a background process group; however, the information may be subsequently changed by a process that is a member of a foreground process group.

Get Terminal Session ID

tcgetsid returns the session ID of the terminal specified by fildes.

DIAGNOSTICS

On success, tcgetpgrp returns the process group ID of the foreground process group associated with the specified terminal. Otherwise, it returns -1 and sets errno to indicate the error.

On success, tcgetsid returns the session ID associated with the specified terminal. Otherwise, it returns -1 and sets errno to indicate the error.

On success, all other functions return a value of 0. Otherwise, they return -1 and set errno to indicate the error.

All of the functions fail if one of more of the following is true:

EBADF The fildes argument is not a valid file descriptor.

ENOTTY The file associated with fildes is not a terminal.

tcsetattr also fails if the following is true:

EINVAL The optional_actions argument is not a proper value, or an attempt was made to change an attribute represented in the termios structure to an unsupported value.

tcsendbreak also fails if the following is true:

EINVAL The device does not support the tcsendbreak function.

tcdrain also fails if one or more of the following is true:

EINTR A signal interrupted the tcdrain function.

EINVAL The device does not support the tcdrain function.

tcflush also fails if the following is true:

EINVAL The device does not support the tcflush function or the queue_selector argument is not a proper value.

tcflow also fails if the following is true:

EINVAL The device does not support the tcflow function or the action argument is not a proper value.

tcgetpgrp also fails if the following is true:

ENOTTY the calling process does not have a controlling terminal, or fildes does not refer to the controlling terminal.

tcsetpgrp also fails if the following is true:

EINVAL pgid is not a valid process group ID .

ENOTTY the calling process does not have a controlling terminal, or fildes does not refer to the controlling terminal, or the controlling terminal is no longer associated with the session of the calling process.

EPERM pgid does not match the process group of an existing process in the same session as the calling process.

tcgetsid also fails if the following is true:

EACCES fildes is a terminal that is not allocated to a session.