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



NAME
     pty - pseudo terminal driver

SYNOPSIS
     /sys/conf/SYSTEM:
	  NPTY _p_t_y_s # pseudo-terminals, in groups of 8

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, _p_t_y_s specifies the number of pseudo terminal
     pairs are configured.

     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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