tcsetattr(3p) — Linux manual page


TCSETATTR(3P)           POSIX Programmer's Manual          TCSETATTR(3P)

PROLOG         top

       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.

NAME         top

       tcsetattr — set the parameters associated with the terminal

SYNOPSIS         top

       #include <termios.h>

       int tcsetattr(int fildes, int optional_actions,
           const struct termios *termios_p);

DESCRIPTION         top

       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

        *  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

        *  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 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
       POSIX.1‐2017 between the call to tcgetattr() and tcsetattr(),
       leaving all other fields and flags unmodified.

       No actions defined by this volume of POSIX.1‐2017, other than a
       call to tcsetattr(), a close of the last file descriptor in the
       system associated with this terminal device, or an open of the
       first file descriptor in the system associated with this terminal
       device (using the O_TTY_INIT flag if it is non-zero and the
       device is not a pseudo-terminal), shall cause any of the terminal
       attributes defined by this volume of POSIX.1‐2017 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 thread is blocking SIGTTOU signals or the
           process is ignoring SIGTTOU signals, the operation completes
           normally and no signal is sent.

        *  Otherwise, a SIGTTOU signal shall be sent to the process

RETURN VALUE         top

       Upon successful completion, 0 shall be returned. Otherwise, -1
       shall be returned and errno set to indicate the error.

ERRORS         top

       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.

       EIO    The process group of the writing process is orphaned, the
              calling thread is not blocking SIGTTOU, and the process is
              not ignoring SIGTTOU.

       ENOTTY The file associated with fildes is not a terminal.

       The following sections are informative.

EXAMPLES         top



       If trying to change baud rates, applications should call
       tcsetattr() then call tcgetattr() in order to determine what baud
       rates were actually selected.

       In general, there are two reasons for an application to change
       the parameters associated with a terminal device:

        1. The device already has working parameter settings but the
           application needs a different behavior, such as non-canonical
           mode instead of canonical mode. The application sets (or
           clears) only a few flags or c_cc[] values. Typically, the
           terminal device in this case is either the controlling
           terminal for the process or a pseudo-terminal.

        2. The device is a modem or similar piece of equipment connected
           by a serial line, and it was not open before the application
           opened it. In this case, the application needs to initialize
           all of the parameter settings ``from scratch''. However,
           since the termios structure may include both standard and
           non-standard parameters, the application cannot just
           initialize the whole structure in an arbitrary way (e.g.,
           using memset()) as this may cause some of the non-standard
           parameters to be set incorrectly, resulting in non-conforming
           behavior of the terminal device. Conversely, the application
           cannot just set the standard parameters, assuming that the
           non-standard parameters will already have suitable values, as
           the device might previously have been used with non-
           conforming parameter settings (and some implementations
           retain the settings from one use to the next). The solution
           is to open the terminal device using the O_TTY_INIT flag to
           initialize the terminal device to have conforming parameter
           settings, obtain those settings using tcgetattr(), and then
           set all of the standard parameters to the desired settings.

RATIONALE         top

       The tcsetattr() function can be interrupted in the following

        *  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(3p).


       Using an input baud rate of 0 to set the input rate equal to the
       output rate may not necessarily be supported in a future version
       of this volume of POSIX.1‐2017.

SEE ALSO         top

       cfgetispeed(3p), tcgetattr(3p)

       The Base Definitions volume of POSIX.1‐2017, Chapter 11, General
       Terminal Interface, termios.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 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 .

       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               2017                     TCSETATTR(3P)

Pages that refer to this page: termios.h(0p)cfsetispeed(3p)cfsetospeed(3p)tcgetattr(3p)