The tcsetattr() function shall set the parameters associated with the
terminal referred to by the open file descriptor fildes (an open file
descriptor associated with a terminal) from the termios structure
referenced by termios_p as follows:
If optional_actions is TCSANOW, the change shall
If optional_actions is TCSADRAIN, the change shall
occur after all output written to fildes is transmitted. This
function should be used when changing parameters that affect output.
If optional_actions is TCSAFLUSH, the change shall
occur after all output written to fildes is transmitted, and all
input so far received but not read shall be discarded before the change is
If the output baud rate stored in the termios structure pointed to by
termios_p is the zero baud rate, B0, the modem control lines shall no
longer be asserted. Normally, this shall disconnect the line.
If the input baud rate stored in the termios structure pointed to by
termios_p is 0, the input baud rate given to the hardware is the same
as the output baud rate stored in the termios structure.
The tcsetattr() function shall return successfully if it was able to
perform any of the requested actions, even if some of the requested actions
could not be performed. It shall set all the attributes that the
implementation supports as requested and leave all the attributes not
supported by the implementation unchanged. If no part of the request can be
honored, it shall return -1 and set errno to [EINVAL]. If the input and
output baud rates differ and are a combination that is not supported, neither
baud rate shall be changed. A subsequent call to tcgetattr() shall
return the actual state of the terminal device (reflecting both the changes
made and not made in the previous tcsetattr() call). The
tcsetattr() function shall not change the values found in the
termios structure under any circumstances.
The effect of tcsetattr() is undefined if the value of the termios
structure pointed to by termios_p was not derived from the result of a
call to tcgetattr() on fildes; an application should modify only
fields and flags defined by this volume of IEEE Std 1003.1-2001
between the call to tcgetattr() and tcsetattr(), leaving all
other fields and flags unmodified.
No actions defined by this volume of IEEE Std 1003.1-2001, other
than a call to tcsetattr() or a close of the last file descriptor in
the system associated with this terminal device, shall cause any of the
terminal attributes defined by this volume of
IEEE Std 1003.1-2001 to change.
If tcsetattr() is called from a process which is a member of a background
process group on a fildes associated with its controlling terminal:
If the calling process is blocking or ignoring SIGTTOU
signals, the operation completes normally and no signal is sent.
Otherwise, a SIGTTOU signal shall be sent to the process
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html