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.TH TCSETATTR "3P" 2013 "IEEE/The Open Group" "POSIX Programmer's Manual"

.SH PROLOG

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.

.SH NAME

tcsetattr

\(em set the parameters associated with the terminal

.SH SYNOPSIS

.LP

.nf

#include <termios.h>

.P

int tcsetattr(int \fIfildes\fP, int \fIoptional_actions\fP,

    const struct termios *\fItermios_p\fP);

.fi

.SH DESCRIPTION

The

\fItcsetattr\fR()

function shall set the parameters associated with the terminal referred

to by the open file descriptor

.IR fildes

(an open file descriptor associated with a terminal) from the

.BR termios

structure referenced by

.IR termios_p

as follows:

.IP " *" 4

If

.IR optional_actions

is TCSANOW, the change shall occur immediately.

.IP " *" 4

If

.IR optional_actions

is TCSADRAIN, the change shall occur after all output written to

.IR fildes

is transmitted. This function should be used when changing parameters

that affect output.

.IP " *" 4

If

.IR optional_actions

is TCSAFLUSH, the change shall occur after all output written to

.IR fildes

is transmitted, and all input so far received but not read shall be

discarded before the change is made.

.P

If the output baud rate stored in the

.BR termios

structure pointed to by

.IR termios_p

is the zero baud rate, B0, the modem control lines shall no longer

be asserted. Normally, this shall disconnect the line.

.P

If the input baud rate stored in the

.BR termios

structure pointed to by

.IR termios_p

is 0, the input baud rate given to the hardware is the same as the

output baud rate stored in the

.BR termios

structure.

.P

The

\fItcsetattr\fR()

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 \(mi1 and set

.IR errno

to

.BR [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

\fItcgetattr\fR()

shall return the actual state of the terminal device (reflecting both

the changes made and not made in the previous

\fItcsetattr\fR()

call). The

\fItcsetattr\fR()

function shall not change the values found in the

.BR termios

structure under any circumstances.

.P

The effect of

\fItcsetattr\fR()

is undefined if the value of the

.BR termios

structure pointed to by

.IR termios_p

was not derived from the result of a call to

\fItcgetattr\fR()

on

.IR fildes ;

an application should modify only fields and flags defined by this volume of POSIX.1\(hy2008

between the call to

\fItcgetattr\fR()

and

\fItcsetattr\fR(),

leaving all other fields and flags unmodified.

.P

No actions defined by this volume of POSIX.1\(hy2008, other than a call to

\fItcsetattr\fR(),

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\(hy2008 to change.

.P

If

\fItcsetattr\fR()

is called from a process which is a member of a background process

group on a

.IR fildes

associated with its controlling terminal:

.IP " *" 4

If the calling thread is blocking SIGTTOU signals or the process is

ignoring SIGTTOU signals, the operation completes normally and no signal

is sent.

.IP " *" 4

Otherwise, a SIGTTOU signal shall be sent to the process group.

.SH "RETURN VALUE"

Upon successful completion, 0 shall be returned. Otherwise,

\(mi1 shall be returned and

.IR errno

set to indicate the error.

.SH ERRORS

The

\fItcsetattr\fR()

function shall fail if:

.TP

.BR EBADF

The

.IR fildes

argument is not a valid file descriptor.

.TP

.BR EINTR

A signal interrupted

\fItcsetattr\fR().

.TP

.BR EINVAL

The

.IR optional_actions

argument is not a supported value, or an attempt was made to change an

attribute represented in the

.BR termios

structure to an unsupported value.

.TP

.BR EIO

The process group of the writing process is orphaned, the calling thread

is not blocking SIGTTOU, and the process is not ignoring SIGTTOU.

.TP

.BR ENOTTY

The file associated with

.IR fildes

is not a terminal.

.LP

.IR "The following sections are informative."

.SH EXAMPLES

None.

.SH "APPLICATION USAGE"

If trying to change baud rates, applications should call

\fItcsetattr\fR()

then call

\fItcgetattr\fR()

in order to determine what baud rates were actually selected.

.P

In general, there are two reasons for an application to change the

parameters associated with a terminal device:

.IP " 1." 4

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

.IR c_cc [\^]

values. Typically, the terminal device in this case is either the

controlling terminal for the process or a pseudo-terminal.

.IP " 2." 4

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

.BR 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

\fImemset\fR())

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

\fItcgetattr\fR(),

and then set all of the standard parameters to the desired settings.

.SH RATIONALE

The

\fItcsetattr\fR()

function can be interrupted in the following situations:

.IP " *" 4

It is interrupted while waiting for output to drain.

.IP " *" 4

It is called from a process in a background process group and SIGTTOU

is caught.

.P

See also the RATIONALE section in

.IR "\fItcgetattr\fR\^(\|)".

.SH "FUTURE DIRECTIONS"

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\(hy2008.

.SH "SEE ALSO"

.IR "\fIcfgetispeed\fR\^(\|)",

.IR "\fItcgetattr\fR\^(\|)"

.P

The Base Definitions volume of POSIX.1\(hy2008,

.IR "Chapter 11" ", " "General Terminal Interface",

.IR "\fB<termios.h>\fP"

.SH COPYRIGHT

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

https://www.kernel.org/doc/man-pages/reporting_bugs.html .