termios(2) termios(2)
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 *termiosp);
int tcsetattr(int fildes, int optionalactions,
const struct termios *termiosp);
int tcsendbreak(int fildes, int duration);
int tcdrain(int fildes);
int tcflush(int fildes, int queueselector);
int tcflow(int fildes, int action);
speedt cfgetospeed(struct termios *termiosp);
int cfsetospeed(const struct termios *termiosp, speedt speed);
speedt cfgetispeed(struct termios *termiosp);
int cfsetispeed(const struct termios *termiosp, speedt speed);
#include <sys/types.h>
#include <termios.h>
pidt tcgetpgrp(int fildes);
int tcsetpgrp(int fildes, pidt pgid);
pidt 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:
tcflagt ciflag; /* input modes */
tcflagt coflag; /* output modes */
tcflagt ccflag; /* control modes */
tcflagt clflag; /* local modes */
cct ccc[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.
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termios(2) termios(2)
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:
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termios(2) termios(2)
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 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 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
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termios(2) termios(2)
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:
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termios(2) termios(2)
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.
SEE ALSO
setsid(2), setpgid(2).
termio(7) in the System Administrator's Reference Manual.
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