pty man page on 4.4BSD

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

     pty — pseudo terminal driver

     pseudo-device pty [count]

     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.

     In configuring, if an optional count is given in the specification, that
     number of pseudo terminal pairs are configured; the default count is 32.

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

     TIOCSTOP	 Stops output to a terminal (e.g. like typing ‘^S’).  Takes no

     TIOCSTART	 Restarts output (stopped by TIOCSTOP or by typing ‘^S’).
		 Takes no parameter.  TIOCSIG Sends the specified signal to
		 the process group members of the pseudo terminal that have it
		 as their controlling terminal.

     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
		 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

		 TIOCPKT_DOSTOP	     whenever t_stopc is ‘^S’ and t_startc is

		 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 out‐
				     put; it can be used by other similar pro‐

     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 specify‐
		 ing (by reference) a nonzero parameter and disabled by speci‐
		 fying (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 operation on the slave
		 side.	A user control command consists of a special 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, 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.

     /dev/pty[p-r][0-9a-f]   master pseudo terminals
     /dev/tty[p-r][0-9a-f]   slave pseudo terminals


     The pty driver appeared in 4.2BSD.

4.2 Berkeley Distribution      December 8, 1994	     4.2 Berkeley Distribution

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