PTY(4)PTY(4)NAMEpty - pseudo terminal driver
SYNOPSIS
pseudo-device pty [ count ]
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 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 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 are configured; the default count
is 32.
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
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 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 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.
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)
