4.4BSD/usr/share/man/cat4/pty.0
PTY(4) BSD Programmer's Manual PTY(4)
NNAAMMEE
ppttyy - pseudo terminal driver
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ppsseeuuddoo--ddeevviiccee ppttyy [_c_o_u_n_t]
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The pty driver provides support for a device-pair termed a _p_s_e_u_d_o
_t_e_r_m_i_n_a_l. A pseudo terminal is a pair of character devices, a _m_a_s_t_e_r de-
vice and a _s_l_a_v_e device. The slave device provides processes an inter-
face 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 de-
vice as input and anything written on the slave device is presented as
input on the master device.
In configuring, if an optional _c_o_u_n_t 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
parameter.
TIOCSTART Restarts output (stopped by TIOCSTOP or by typing `^S').
Takes no parameter.
TIOCPKT Enable/disable _p_a_c_k_e_t 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 in-
clusive-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___s_t_o_p_c is `^S' and _t___s_t_a_r_t_c 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) 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-
grams.
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 en-
abled 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 us-
er 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 re-
ceived 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 re-
mote line editing in a window manager, or whenever flow con-
trolled input is required.
FFIILLEESS
/dev/pty[p-r][0-9a-f] master pseudo terminals
/dev/tty[p-r][0-9a-f] slave pseudo terminals
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None.
HHIISSTTOORRYY
The ppttyy driver appeared in 4.2BSD.
4.2 Berkeley Distribution June 5, 1993 2