DragonFly On-Line Manual Pages
PTY(4) DragonFly Kernel Interfaces Manual PTY(4)
NAME
pty - pseudo terminal driver
SYNOPSIS
pseudo-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
presented 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
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(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)
(net/bsdrcmds) and rlogind(8)
(net/bsdrcmds) 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(2) 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(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.
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/pts/[0-9]+ slave pseudo terminals
/dev/ptmx master pseudo terminal clone device
DIAGNOSTICS
None.
SEE ALSO
tty(4) posix_openpt(3) openpty(3) pty(3)
HISTORY
The pty driver appeared in 4.2BSD.
DragonFly 6.5-DEVELOPMENT December 31, 2017 DragonFly 6.5-DEVELOPMENT