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 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 POSIX.1‐2008 between the
       call to tcgetattr() and tcsetattr(), leaving all other fields and
       flags unmodified.

       No actions defined by this volume of POSIX.1‐2008, 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.1‐2008 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

        *  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 group.

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.1‐2008.

SEE ALSO         top

       cfgetispeed(3p), tcgetattr(3p)

       The Base Definitions volume of POSIX.1‐2008, 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, 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 .

       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                       TCSETATTR(3P)

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