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



PPRROOLLOOGG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

NNAAMMEE
       tcsetattr -- set the parameters associated with the terminal

SSYYNNOOPPSSIISS
       #include <termios.h>

       int tcsetattr(int _f_i_l_d_e_s, int _o_p_t_i_o_n_a_l___a_c_t_i_o_n_s,
           const struct termios *_t_e_r_m_i_o_s___p);

DDEESSCCRRIIPPTTIIOONN
       The _t_c_s_e_t_a_t_t_r() function shall set the parameters associated with the
       terminal referred to by the open file descriptor _f_i_l_d_e_s (an open file
       descriptor associated with a terminal) from the tteerrmmiiooss structure
       referenced by _t_e_r_m_i_o_s___p as follows:

        *  If _o_p_t_i_o_n_a_l___a_c_t_i_o_n_s is TCSANOW, the change shall occur immediately.

        *  If _o_p_t_i_o_n_a_l___a_c_t_i_o_n_s is TCSADRAIN, the change shall occur after all
           output written to _f_i_l_d_e_s is transmitted. This function should be
           used when changing parameters that affect output.

        *  If _o_p_t_i_o_n_a_l___a_c_t_i_o_n_s is TCSAFLUSH, the change shall occur after all
           output written to _f_i_l_d_e_s 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 tteerrmmiiooss structure pointed to by
       _t_e_r_m_i_o_s___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 tteerrmmiiooss structure pointed to by
       _t_e_r_m_i_o_s___p is 0, the input baud rate given to the hardware is the same
       as the output baud rate stored in the tteerrmmiiooss structure.

       The _t_c_s_e_t_a_t_t_r() 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 _e_r_r_n_o to [[EEIINNVVAALL]].
       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
       _t_c_g_e_t_a_t_t_r() shall return the actual state of the terminal device
       (reflecting both the changes made and not made in the previous
       _t_c_s_e_t_a_t_t_r() call). The _t_c_s_e_t_a_t_t_r() function shall not change the values
       found in the tteerrmmiiooss structure under any circumstances.

       The effect of _t_c_s_e_t_a_t_t_r() is undefined if the value of the tteerrmmiiooss
       structure pointed to by _t_e_r_m_i_o_s___p was not derived from the result of a
       call to _t_c_g_e_t_a_t_t_r() on _f_i_l_d_e_s; an application should modify only fields
       and flags defined by this volume of POSIX.1-2017 between the call to
       _t_c_g_e_t_a_t_t_r() and _t_c_s_e_t_a_t_t_r(), leaving all other fields and flags
       unmodified.

       No actions defined by this volume of POSIX.1-2017, other than a call to
       _t_c_s_e_t_a_t_t_r(), 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 _t_c_s_e_t_a_t_t_r() is called from a process which is a member of a
       background process group on a _f_i_l_d_e_s 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 group.

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

EERRRROORRSS
       The _t_c_s_e_t_a_t_t_r() function shall fail if:

       EEBBAADDFF  The _f_i_l_d_e_s argument is not a valid file descriptor.

       EEIINNTTRR  A signal interrupted _t_c_s_e_t_a_t_t_r().

       EEIINNVVAALL The _o_p_t_i_o_n_a_l___a_c_t_i_o_n_s argument is not a supported value, or an
              attempt was made to change an attribute represented in the
              tteerrmmiiooss structure to an unsupported value.

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

       EENNOOTTTTYY The file associated with _f_i_l_d_e_s is not a terminal.

       _T_h_e _f_o_l_l_o_w_i_n_g _s_e_c_t_i_o_n_s _a_r_e _i_n_f_o_r_m_a_t_i_v_e_.

EEXXAAMMPPLLEESS
       None.

AAPPPPLLIICCAATTIIOONN UUSSAAGGEE
       If trying to change baud rates, applications should call _t_c_s_e_t_a_t_t_r()
       then call _t_c_g_e_t_a_t_t_r() 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___c_c[] 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 tteerrmmiiooss
           structure may include both standard and non-standard parameters,
           the application cannot just initialize the whole structure in an
           arbitrary way (e.g., using _m_e_m_s_e_t()) 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
           _t_c_g_e_t_a_t_t_r(), and then set all of the standard parameters to the
           desired settings.

RRAATTIIOONNAALLEE
       The _t_c_s_e_t_a_t_t_r() 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 _t_c_g_e_t_a_t_t_r().

FFUUTTUURREE DDIIRREECCTTIIOONNSS
       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.

SSEEEE AALLSSOO
       _c_f_g_e_t_i_s_p_e_e_d(), _t_c_g_e_t_a_t_t_r()

       The Base Definitions volume of POSIX.1-2017, _C_h_a_p_t_e_r _1_1, _G_e_n_e_r_a_l
       _T_e_r_m_i_n_a_l _I_n_t_e_r_f_a_c_e, <<tteerrmmiiooss..hh>>

CCOOPPYYRRIIGGHHTT
       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 http://www.opengroup.org/unix/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
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                         TCSETATTR(3)
