termios(3t)termios(3t)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 <unistd.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 */
speed_t c_ospeed; /* output speed */
speed_t c_ispeed; /* input speed; not supported */
cc_t c_cc[NCCS]; /* control chars */
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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.
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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 TCIOFF, 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
speed_t values passed to and returned from these functions are integral
values directly containing the desired rate in bits per second. The
integer 38400, for example, represents 38400 bps. Exactly which values
are supported depends on the type of hardware; see serial(7) for more
information. The tcsetattr function will return EINVAL if the specified
rate is not supported by the hardware. The names in this table represent
common rates, and are defined for convenience 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
B57600 57600 baud B76800 76800 baud
B115200 115200 baud
cfgetospeed gets the output baud rate stored 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 asserted. Normally, this disconnects the line.
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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, cfgetispeed returns the input baud rate from the termios
structure.
On success, cfgetospeed returns the output baud rate from the termios
structure.
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.
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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.
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termios(3t)termios(3t)SEE ALSOsetsid(2), setpgid(2), termio(7), serial(7)
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