pty(7)
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pty, pts, ptc Special File
pseudo-terminal master/slave pseudo-device pair
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DESCRIPTION
A pseudo-terminal (pty) is a pair of character devices, a master
device and a slave device. The master device is supported by the
ptc driver and the slave device is supported by the pts driver.
The slave device provides processes a standard tty interface as
described in termio(7) and tty(7). However, whereas other
devices which provide the tty interface 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.
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. The ioctl parameter is the
address of an int, whose value determines whether packet
mode is to be enabled (non-zero value) or disabled (zero
value). 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.
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pty(7)
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.
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/ttyp* /dev/ptyp*
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pty(7)
SEE ALSO
termio(7), tty(7)
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