4.3BSD-UWisc/man/cat4/pty.4

PTY(4)              UNIX Programmer's Manual               PTY(4)



NAME
     pty - pseudo terminal driver

SYNOPSIS
     pseudo-device pty [ count ]

DESCRIPTION
     The _p_t_y driver provides support for a device-pair termed a
     _p_s_e_u_d_o _t_e_r_m_i_n_a_l.  A pseudo terminal is a pair of character
     devices, a _m_a_s_t_e_r device and a _s_l_a_v_e device.  The slave dev-
     ice provides processes an interface identical to that
     described in _t_t_y(4).  However, whereas all other devices
     which provide the interface described in _t_t_y(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 writ-
     ten 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.

     In configuring, if an optional ``count'' is given in the
     specification, that number of pseudo terminal pairs are con-
     figured; the default count is 32.

     The following _i_o_c_t_l 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 _p_a_c_k_e_t mode.  Packet mode is enabled by
          specifying (by reference) a nonzero parameter and dis-
          abled by specifying (by reference) a zero parameter.
          When applied to the master side of a pseudo terminal,
          each subsequent _r_e_a_d from the terminal will return data
          written on the slave part of the pseudo terminal pre-
          ceded 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



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PTY(4)              UNIX Programmer's Manual               PTY(4)



               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__s_t_o_p_c is ^S and _t__s_t_a_r_t_c 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 _s_e_l_e_c_t for exceptional conditions.

          This mode is used by _r_l_o_g_i_n(1C) and _r_l_o_g_i_n_d(8C) 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 _i_o_c_t_l 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 refer-
          ence) a zero parameter.  Each subsequent _r_e_a_d 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 spe-
          cial _i_o_c_t_l 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 _r_e_a_d from the master side.  The _i_o_c_t_l
          UIOCCMD(0) is a no-op that may be used to probe for the
          existence of this facility.  As with TIOCPKT mode, com-
          mand operations may be detected with a _s_e_l_e_c_t for
          exceptional conditions.

     TIOCREMOTE
          A mode for the master half of a pseudo terminal,
          independent of TIOCPKT.  This mode causes input to the
          pseudo terminal to be flow controlled and not input
          edited (regardless of the terminal mode).  Each write



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PTY(4)              UNIX Programmer's Manual               PTY(4)



          to the control terminal produces a record boundary for
          the process reading the terminal.  In normal usage, a
          write of data is like the data typed as a line on the
          terminal; a write of 0 bytes is like typing an end-of-
          file character.  TIOCREMOTE can be used when doing
          remote line editing in a window manager, or whenever
          flow controlled input is required.

FILES
     /dev/pty[p-r][0-9a-f]    master pseudo terminals
     /dev/tty[p-r][0-9a-f]    slave pseudo terminals

DIAGNOSTICS
     None.









































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