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BSD 2.11 - man page for pty (bsd section 4)

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PTY(4)											   PTY(4)

NAME
       pty - pseudo terminal driver

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

DESCRIPTION
       The pty driver provides support for a device-pair termed a pseudo terminal.  A pseudo ter-
       minal is a pair of character devices, a master device  and  a  slave  device.   The  slave
       device  provides  processes  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 manipulat-
       ing 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.

       In configuring, ptys specifies the number of pseudo terminal pairs are configured.

       The following ioctl 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 from the ter-
	      minal 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 for exceptional conditions.

	      This  mode  is  used  by	rlogin(1C)  and rlogind(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 ioctl 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 parame-
	      ter  and	disabled  by specifying (by reference) a zero parameter.  Each subsequent
	      read 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 opera-
	      tion on the slave side.  A user control command consists of a special ioctl  opera-
	      tion  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  from  the  master  side.  The ioctl 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 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 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.

4.2 Berkeley Distribution		   May 19, 1986 				   PTY(4)
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