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pty(4)

NAME

     pty -- pseudo terminal driver

SYNOPSIS

     device pty

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 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 pre-
     sented as input on the master device.

     The following ioctl(2) 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 speci-
		 fying (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(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

     TIOCUCNTL	 Enable/disable a mode that allows a small number of simple
		 user ioctl(2) commands to be passed through the pseudo-termi-
		 nal, 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 reference) a zero 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 control 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.

FILES

     /dev/pty[p-sP-S][0-9a-v]	master pseudo terminals
     /dev/tty[p-sP-S][0-9a-v]	slave pseudo terminals

DIAGNOSTICS

     None.

SEE ALSO

     tty(4)

HISTORY

     The pty driver appeared in 4.2BSD.

FreeBSD 5.4		       November 30, 1993		   FreeBSD 5.4

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