TCSETATTR(P) POSIX Programmer's Manual TCSETATTR(P)
tcsetattr - set the parameters associated with the terminal
int tcsetattr(int fildes, int optional_actions,
const struct termios *termios_p);
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 occur immediately.
* 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
* 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 made.
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
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
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 applica-
tion 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 unmod-
No actions defined by this volume of IEEE Std 1003.1-2001, other than a call to tcse-
tattr() 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 group.
Upon successful completion, 0 shall be returned. Otherwise, -1 shall be returned and errno
set to indicate the error.
The tcsetattr() function shall fail if:
EBADF The fildes argument is not a valid file descriptor.
EINTR A signal interrupted tcsetattr().
EINVAL The optional_actions argument is not a supported value, or an attempt was made to
change an attribute represented in the termios structure to an unsupported value.
ENOTTY The file associated with fildes is not a terminal.
The tcsetattr() function may fail if:
EIO The process group of the writing process is orphaned, and the writing process is
not ignoring or blocking SIGTTOU.
The following sections are informative.
If trying to change baud rates, applications should call tcsetattr() then call tcgetattr()
in order to determine what baud rates were actually selected.
The tcsetattr() function can be interrupted in the following situations:
* It is interrupted while waiting for output to drain.
* It is called from a process in a background process group and SIGTTOU is caught.
See also the RATIONALE section in tcgetattr() .
Using an input baud rate of 0 to set the input rate equal to the output rate may not nec-
essarily be supported in a future version of this volume of IEEE Std 1003.1-2001.
cfgetispeed() , tcgetattr() , the Base Definitions volume of IEEE Std 1003.1-2001, Chapter
11, General Terminal Interface, <termios.h>, <unistd.h>
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 orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 TCSETATTR(P)