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pty (4)
  • pty (3) ( FreeBSD man: Библиотечные вызовы )
  • >> pty (4) ( FreeBSD man: Специальные файлы /dev/* )
  • pty (7) ( Solaris man: Макропакеты и соглашения )
  • pty (7) ( Linux man: Макропакеты и соглашения )

  • BSD mandoc
     

    NAME

    
    
    pty
    
     - pseudo terminal driver
    
     
    

    SYNOPSIS

    device pty  

    DESCRIPTION

    The driver provides support for a device-pair termed a pseudo terminal A pseudo terminal is a pair of character devices, a master device and a slave device. The slave device provides to a process an interface identical to that described in tty(4). However, whereas all other devices which provide the interface described in tty(4) have a hardware device of some sort behind them, the slave device has, instead, another process manipulating it through the master half of the pseudo terminal. That is, anything written on the master device is given to the slave device as input and anything written on the slave device is presented as input on the master device.

    The following ioctl(2) calls apply only to pseudo terminals:

    TIOCSTOP
    Stops output to a terminal (e.g. like typing `^S' ) . Takes no parameter.
    TIOCSTART
    Restarts output (stopped by TIOCSTOP or by typing `^S' ) . Takes no parameter.
    TIOCPKT
    Enable/disable packet mode. Packet mode is enabled by specifying (by reference) a nonzero parameter and disabled by specifying (by reference) a zero parameter. When applied to the master side of a pseudo terminal, each subsequent read(2) from the terminal will return data written on the slave part of the pseudo terminal preceded by a zero byte (symbolically defined as TIOCPKT_DATA ) or a single byte reflecting control status information. In the latter case, the byte is an inclusive-or of zero or more of the bits:

    TIOCPKT_FLUSHREAD
    whenever the read queue for the terminal is flushed.
    TIOCPKT_FLUSHWRITE
    whenever the write queue for the terminal is flushed.
    TIOCPKT_STOP
    whenever output to the terminal is stopped a la `^S'
    TIOCPKT_START
    whenever output to the terminal is restarted.
    TIOCPKT_DOSTOP
    whenever t_stopc is `^S' and t_startc is `^Q'
    TIOCPKT_NOSTOP
    whenever the start and stop characters are not `^S/^Q'

    While this mode is in use, the presence of control status information to be read from the master side may be detected by a select(2) for exceptional conditions.

    This mode is used by rlogin(1) and rlogind(8) to implement a remote-echoed, locally `^S/^Q' flow-controlled remote login with proper back-flushing of output; it can be used by other similar programs.

    TIOCUCNTL
    Enable/disable a mode that allows a small number of simple user ioctl(2) commands to be passed through the pseudo-terminal, using a protocol similar to that of TIOCPKT The TIOCUCNTL and TIOCPKT modes are mutually exclusive. This mode is enabled from the master side of a pseudo terminal by specifying (by reference) a nonzero parameter and disabled by specifying (by reference) a zero parameter. Each subsequent read(2) from the master side will return data written on the slave part of the pseudo terminal preceded by a zero byte, or a single byte reflecting a user control operation on the slave side. A user control command consists of a special ioctl(2) operation with no data; the command is given as UIOCCMD (n) where n is a number in the range 1-255. The operation value n will be received as a single byte on the next read(2) from the master side. The ioctl(2) UIOCCMD (0) is a no-op that may be used to probe for the existence of this facility. As with TIOCPKT mode, command operations may be detected with a select(2) for exceptional conditions.

    There is currently two systems available: the original BSD and a SysVR4 pts-like implementation. It is possible to switch between the two implementations by setting the kern.pts.enable sysctl. Setting it to 0 will use the BSD to non-zero the pts implementation. It defaults to 0. It is possible to set the maximum number of ptys which can be allocated at the same time with the kern.pts.max sysctl. It defaults to 1000. It is not recommended to use more than 1000 pseudo-terminals, as all software which use utmp(5) will not be able to handle pseudo-terminals with number superior to 999.

    The pts implementation also supports the TIOCGPTN ioctl(2) call, which takes a pointer to an Vt unsigned int as a parameter and provides the number of the pty.  

    FILES

    The files used by the BSD pseudo terminals implementation are:

    /dev/pty[p-sP-S][0-9a-v]
    master pseudo terminals
    /dev/tty[p-sP-S][0-9a-v]
    slave pseudo terminals

    The files used by the pts implementation are:

    /dev/ptmx
    control device, returns a file descriptor to a new master pseudo terminal when opened.
    /dev/pty[num]
    master pseudo terminals
    /dev/pts/[num]
    slave pseudo terminals

     

    DIAGNOSTICS

    None.  

    SEE ALSO

    tty(4)  

    HISTORY

    The driver appeared in BSD 4.2


     

    Index

    NAME
    SYNOPSIS
    DESCRIPTION
    FILES
    DIAGNOSTICS
    SEE ALSO
    HISTORY


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