TCSETS(2const)

💖 TCSETS — get and set terminal attributes 💖

okay bestie, welcome to the TCSETS(2const) page, this is the one where we mess with terminal (serial port) attributes and honestly? it's giving main character energy. 💅

Quick heads-up on the names: this whole family is TCGETS, TCSETS, TCSETSW, TCSETSF, TCGETS2, TCSETS2, TCSETSW2, TCSETSF2, TCGETA, TCSETA, TCSETAW, and TCSETAF — get and set terminal attributes, collectively, as a little squad. 🫶

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📚 LIBRARY

Standard C library (libc, -lc). yes girl, it's in libc, nothing exotic. ✨

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✨ SYNOPSIS ✨

#include <asm/termbits.h>  /* Definition of TC* constants */
#include <sys/ioctl.h>

int ioctl(int fd, TCGETS, struct termios *argp);
int ioctl(int fd, TCSETS, const struct termios *argp);
int ioctl(int fd, TCSETSW, const struct termios *argp);
int ioctl(int fd, TCSETSF, const struct termios *argp);

int ioctl(int fd, TCGETS2, struct termios2 *argp);
int ioctl(int fd, TCSETS2, const struct termios2 *argp);
int ioctl(int fd, TCSETSW2, const struct termios2 *argp);
int ioctl(int fd, TCSETSF2, const struct termios2 *argp);

[[deprecated]] int ioctl(int fd, TCGETA, struct termio *argp);
[[deprecated]] int ioctl(int fd, TCSETA, const struct termio *argp);
[[deprecated]] int ioctl(int fd, TCSETAW, const struct termio *argp);
[[deprecated]] int ioctl(int fd, TCSETAF, const struct termio *argp);

#include <asm/termbits.h>

struct termios;
struct termios2;
struct [[deprecated]] termio;

🚨 see those [[deprecated]] tags? that's not decor, bestie. those ones are on their way out. we'll get to them.

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🌸 DESCRIPTION 🌸

okay so here's the tea on each one, one by one, no skipping. 💖

• TCGETS — Equivalent to tcgetattr(fd, argp).

Get the current serial port settings. 📖 it's a read, it just looks at the vibe of your port.

• TCSETS — Equivalent to tcsetattr(fd, TCSANOW, argp).

Set the current serial port settings. boom, applied immediately. ⚡

• TCSETSW — Equivalent to tcsetattr(fd, TCSADRAIN, argp).

Allow the output buffer to drain, and set the current serial port settings. 🚰 let everything finish flushing out first, then change.

• TCSETSF — Equivalent to tcsetattr(fd, TCSAFLUSH, argp).

Allow the output buffer to drain, discard pending input, and set the current serial port settings. 💀 output drains, input gets thrown in the bin, and then the new settings land. ruthless but iconic.

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The following four ioctls are just like TCGETS, TCSETS, TCSETSW, TCSETSF, except that they take a struct termios2 * instead of a struct termios *. 👀 If the structure member c_cflag contains the flag BOTHER, then the baud rate is stored in the structure members c_ispeed and c_ospeed as integer values. These ioctls are not supported on all architectures. 🥲

• TCGETS2
• TCSETS2
• TCSETSW2
• TCSETSF2

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The following four ioctls are just like TCGETS, TCSETS, TCSETSW, TCSETSF, except that they take a struct termio * instead of a struct termios *. 🫶 (yes, termio, no s. they're cousins, not twins.)

• TCGETA
• TCSETA
• TCSETAW
• TCSETAF

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🎀 RETURN VALUE 🎀

On success, 0 is returned. ✨ On error, -1 is returned and errno is set to indicate the error. it said what it said. 💅

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💀 ERRORS 💀

• EPERM — Insufficient permission. not yours, bestie, go get some permissions. 🙈

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🦋 HISTORY 🦋

The girls TCGETS2, TCSETS2, TCSETSW2, TCSETSF2 all showed up in Linux 2.6.20. ⭐

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⚠️ CAVEATS ⚠️

struct termios from <asm/termbits.h> is different and incompatible with struct termios from <termios.h>. 😭 These ioctl calls require struct termios from <asm/termbits.h>.

no cap, if you grab the wrong termios you WILL be confused and it will NOT be the compiler's fault. check your #include, queen. 👑

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🌈 EXAMPLES 🌈

Get or set arbitrary baudrate on the serial port. 🐎

/* SPDX-License-Identifier: GPL-2.0-or-later */

#include <asm/termbits.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <unistd.h>

int
main(int argc, char *argv[])
{
#if !defined BOTHER
    fprintf(stderr, "BOTHER is unsupported\n");
    /* Program may fallback to TCGETS/TCSETS with Bnnn constants */
    exit(EXIT_FAILURE);
#else
    /* Declare tio structure, its type depends on supported ioctl */
# if defined TCGETS2
    struct termios2 tio;
# else
    struct termios tio;
# endif
    int fd, rc;

    if (argc != 2 && argc != 3 && argc != 4) {
        fprintf(stderr, "Usage: %s device [output [input] ]\n", argv[0]);
        exit(EXIT_FAILURE);
    }

    fd = open(argv[1], O_RDWR | O_NONBLOCK | O_NOCTTY);
    if (fd < 0) {
        perror("open");
        exit(EXIT_FAILURE);
    }

    /* Get the current serial port settings via supported ioctl */
# if defined TCGETS2
    rc = ioctl(fd, TCGETS2, &tio);
# else
    rc = ioctl(fd, TCGETS, &tio);
# endif
    if (rc) {
        perror("TCGETS");
        close(fd);
        exit(EXIT_FAILURE);
    }

    /* Change baud rate when more arguments were provided */
    if (argc == 3 || argc == 4) {
        /* Clear the current output baud rate and fill a new value */
        tio.c_cflag &= ~CBAUD;
        tio.c_cflag |= BOTHER;
        tio.c_ospeed = atoi(argv[2]);

        /* Clear the current input baud rate and fill a new value */
        tio.c_cflag &= ~(CBAUD << IBSHIFT);
        tio.c_cflag |= BOTHER << IBSHIFT;
        /* When 4th argument is not provided reuse output baud rate */
        tio.c_ispeed = (argc == 4) ? atoi(argv[3]) : atoi(argv[2]);

        /* Set new serial port settings via supported ioctl */
# if defined TCSETS2
        rc = ioctl(fd, TCSETS2, &tio);
# else
        rc = ioctl(fd, TCSETS, &tio);
# endif
        if (rc) {
            perror("TCSETS");
            close(fd);
            exit(EXIT_FAILURE);
        }

        /* And get new values which were really configured */
# if defined TCGETS2
        rc = ioctl(fd, TCGETS2, &tio);
# else
        rc = ioctl(fd, TCGETS, &tio);
# endif
        if (rc) {
            perror("TCGETS");
            close(fd);
            exit(EXIT_FAILURE);
        }
    }

    close(fd);

    printf("output baud rate: %u\n", tio.c_ospeed);
    printf("input baud rate: %u\n", tio.c_ispeed);

    exit(EXIT_SUCCESS);
#endif
}

ate, honestly. 🍓 that whole #if defined ladder is giving "works everywhere, panics nowhere".

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🔥 SEE ALSO 🔥

• ioctl(2)
• ioctl_tty(2)
• termios(7)

go read those too, they're the supporting cast and they eat. 👑

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mwah 💜 this page was brought to you by Linux man-pages 6.20, dated 2026-07-02, and honestly it slayed. go set some terminal attributes, bestie, you've got this. 🎀✨🦋