2.11BSD#431 - /usr/man/cat4/pty.0

PTY(4)		    UNIX Programmer's Manual		   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 terminal is a pair of character
     devices, a master device and a slave device.  The slave dev-
     ice 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 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, 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 dis-
	  abled by specifying (by reference) a zero parameter.
	  When applied to the master side of a pseudo terminal,
	  each subsequent read 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_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 parameter and disabled by specifying (by refer-
	  ence) 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 operation on the
	  slave side.  A user control command consists of a spe-
	  cial ioctl 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 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, com-
	  mand 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


Printed 11/26/99	  May 19, 1986				2


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.


Printed 11/26/99	  May 19, 1986				3