| TTY(4) | Device Drivers Manual | TTY(4) | 
tty —
#include <sys/ioctl.h>
The /dev/ttyXX special file is used for dial-in modems and terminals. When a user logs into the system on one of these hardware terminal ports, the system has already opened the associated device and prepared the line for normal interactive use (see getty(8)).
The /dev/dtyXX special file is a SunOS-compatible dial-out device. Unlike the dial-in device, opening the dial-out device never blocks. If the corresponding dial-in device is already opened (not blocked in the open waiting for carrier), then the dial-out open will fail immediately; otherwise it will succeed immediately. While the dial-out device is open, the dial-in device may not be opened. If the dial-in open is blocking, it will wait until the dial-out device is closed (and carrier is detected); otherwise it will fail immediately.
There is also a special case of a terminal file that connects not to a hardware terminal port, but to another program on the other side. These special terminal devices are called ptys (pseudo terminals) and provide the mechanism necessary to give users the same interface to the system when logging in over a network (using rlogin(1), or telnet(1) for example.) Even in these cases the details of how the terminal file was opened and set up is already handled by special software in the system. Thus, users do not normally need to worry about the details of how these lines are opened or used. Also, these lines are often used for dialing out of a system (through an out-calling modem), but again the system provides programs that hide the details of accessing these terminal special files (see tip(1)).
When an interactive user logs in, the system prepares the line to behave in a certain way (called a line discipline), the particular details of which is described in stty(1) at the command level, and in termios(4) at the programming level. A user may be concerned with changing settings associated with his particular login terminal and should refer to the preceding man pages for the common cases. The remainder of this man page is concerned with describing details of using and controlling terminal devices at a low level, such as that possibly required by a program wishing to provide features similar to those provided by the system.
termios line discipline is associated with
  the file. This is the primary line discipline that is used in most cases and
  provides the semantics that users normally associate with a terminal. When the
  termios line discipline is in effect, the terminal
  file behaves and is operated according to the rules described in
  termios(4). Please refer to
  that man page for a full description of the terminal semantics. The operations
  described here generally represent features common across all
  line disciplines, however some of these calls may not make
  sense in conjunction with a line discipline other than
  termios, and some may not be supported by the
  underlying hardware (or lack thereof, as in the case of ptys).
and would be called on the terminal associated with file descriptor zero by the following code fragment:
ioctl(0, TIOCSLINED, "termios");
TIOCSLINED
    char name[32]TIOCGLINED
    char name[32]TIOCSBRK
    voidTIOCCBRK
    voidTIOCSDTR
    voidTIOCCDTR
    voidTIOCGPGRP
    int *tpgrpTIOCSPGRP
    int *tpgrpTIOCGETA
    struct termios *termTIOCSETA
    struct termios *termTCSANOW option.TIOCSETAW
    struct termios *termTCSADRAIN option.TIOCSETAF
    struct termios *termTCSAFLUSH option.TIOCOUTQ
    int *numTIOCSTI
    char *cpTIOCNOTTY
    voidTIOCNOTTY on that file descriptor.
    The current system does not allocate a controlling terminal to
        a process on an open() call: there is a specific
        ioctl called TIOCSCTTY to make a terminal the
        controlling terminal. In addition, a program can
        fork() and call the
        setsid() system call which will place the
        process into its own session - which has the effect of disassociating it
        from the controlling terminal. This is the new and preferred method for
        programs to lose their controlling terminal.
TIOCSTOP
    voidTIOCSTART
    voidTIOCSCTTY
    voidTIOCDRAIN
    voidTIOCEXCL
    voidTIOCNXCL
    voidTIOCFLUSH
    int *whatFREAD bit as defined in
      <sys/fcntl.h>, then all
      characters in the input queue are cleared. If it contains the
      FWRITE bit, then all characters in the output
      queue are cleared. If the value of the integer is zero, then it behaves as
      if both the FREAD and
      FWRITE bits were set (i.e. clears both
    queues).TIOCGWINSZ
    struct winsize *ws<sys/ioctl.h>.TIOCSWINSZ
    struct winsize *wsTIOCGQSIZE
    int *qsizeTIOCSQSIZE
    int *qsize1024 and 65536 and input
      values are converted to a power of two. All pending input and output is
      dropped.TIOCCONS
    int *onTIOCMSET
    int *stateThis call sets the terminal modem state to that represented by state. Not all terminals may support this.
TIOCMGET
    int *stateTIOCMBIS
    int *stateTIOCMBIC
    int *stateTIOCSFLAGS
    int *stateCLOCAL flag on open.CRTSCTS flag on open.MDMBUF flag on open.This call sets the serial port state to that represented by state. Not all serial ports may support this.
TIOCGFLAGS
    int *stateTIOCSETD
    int *ldisc<sys/ttycom.h> and are:
    
    TIOCGETD
    int *ldisc| September 7, 2019 | NetBSD 10.1 |