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NetBSD 6.1.5 - man page for pty (netbsd section 4)

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PTY(4)				   BSD Kernel Interfaces Manual 			   PTY(4)

NAME
     pty -- pseudo terminal driver

SYNOPSIS
     pseudo-device pty [count]

DESCRIPTION
     The pty driver provides support for a device-pair termed a pseudo terminal.  A pseudo termi-
     nal 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.

     In configuring, if an optional count is given in the specification, that number of pseudo
     terminal pairs is initially configured; the default count is 16.  Additional pseudo terminal
     pairs are allocated on as-needed basis, maximum number of them is controlled via
     kern.maxptys sysctl (defaults to 992).

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

     TIOCEXT	 Enable/disable ``external processing''.  This affects delivery of TIOCPKT_IOCTL
		 packets.  External processing is enabled by specifying (by reference) a nonzero
		 int parameter and disabled by specifying (by reference) a zero int parameter.

		 TIOCEXT is reset to its default (disabled) when the slave closes the pty.

     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 int parameter and disabled by specifying (by reference) a zero int
		 parameter.  When applied to the master side of a pseudo terminal, each subse-
		 quent 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.

		 TIOCPKT_IOCTL	     When this bit is set, the slave has changed the termios(4)
				     structure (TTY state), and the remainder of the data read
				     from the master side of the pty is the new termios(4) struc-
				     ture.  The master side of the pty can also use tcgetattr(3)
				     to read the new termios(4) structure.

				     The master will not read packets with the bit TIOCPKT_IOCTL
				     set until it has activated ``external processing'' using
				     TIOCEXT.

				     This is used by telnetd(8) to implement TELNET "line mode" -
				     it allows the telnetd(8) to detect tty(4) state changes by
				     the slave, and negotiate the appropriate TELNET protocol
				     equivalents with the remote peer.

     TIOCUCNTL	 Enable/disable a mode that allows a small number of simple user ioctl(2) com-
		 mands 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 refer-
		 ence) a nonzero int parameter and disabled by specifying (by reference) a zero
		 int 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 con-
		 trol 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.

     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-zP-T][0-9a-zA-Z]   master pseudo terminals
     /dev/tty[p-zP-T][0-9a-zA-Z]   slave pseudo terminals

DIAGNOSTICS
     None.

SEE ALSO
     ioctl(2), read(2), select(2), write(2), openpty(3), tty(4)

HISTORY
     The pty driver appeared in 4.2BSD.

BSD					 February 1, 2011				      BSD
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