This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
The tcgetattr() function shall get the parameters associated with the
terminal referred to by fildes and store them in the termios
structure referenced by termios_p. The fildes argument is an open
file descriptor associated with a terminal.
The termios_p argument is a pointer to a termios structure.
The tcgetattr() operation is allowed from any process.
If the terminal device supports different input and output baud
rates, the baud rates stored in the termios structure returned by
tcgetattr() shall reflect the actual baud rates, even if they are
equal. If differing baud rates are not supported, the rate returned
as the output baud rate shall be the actual baud rate. If the
terminal device does not support split baud rates, the input baud
rate stored in the termios structure shall be the output rate (as one
of the symbolic values).
Care must be taken when changing the terminal attributes.
Applications should always do a tcgetattr(), save the termios
structure values returned, and then do a tcsetattr(), changing only
the necessary fields. The application should use the values saved
from the tcgetattr() to reset the terminal state whenever it is done
with the terminal. This is necessary because terminal attributes
apply to the underlying port and not to each individual open
instance; that is, all processes that have used the terminal see the
latest attribute changes.
A program that uses these functions should be written to catch all
signals and take other appropriate actions to ensure that when the
program terminates, whether planned or not, the terminal device's
state is restored to its original state.
Existing practice dealing with error returns when only part of a
request can be honored is based on calls to the ioctl() function. In
historical BSD and System V implementations, the corresponding
ioctl() returns zero if the requested actions were semantically
correct, even if some of the requested changes could not be made.
Many existing applications assume this behavior and would no longer
work correctly if the return value were changed from zero to −1 in
Note that either specification has a problem. When zero is returned,
it implies everything succeeded even if some of the changes were not
made. When −1 is returned, it implies everything failed even though
some of the changes were made.
Applications that need all of the requested changes made to work
properly should follow tcsetattr() with a call to tcgetattr() and
compare the appropriate field values.
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) 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.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the
source files to man page format. To report such errors, see
IEEE/The Open Group 2013 TCGETATTR(3P)