In configuring, if an optional count is given in the specification, that number of pseudo terminal pairs is initially configured; the default count is 16. Additional pseudo terminal pairs are allocated on as-needed basis, maximum number of them is controlled via kern.maxptys sysctl (defaults to 992).
The following ioctl(2) calls apply only to pseudo terminals:
TIOCSTOPTIOCSTARTTIOCSTOP
or by typing
`^S').
Takes no parameter.
TIOCPKTTIOCPKT_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_FLUSHREADTIOCPKT_FLUSHWRITETIOCPKT_STOPTIOCPKT_STARTTIOCPKT_DOSTOPTIOCPKT_NOSTOPWhile 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 output; it can be used by other similar programs.
TIOCPKT_IOCTLThis is used by telnetd(8) to implement TELNET "line mode" - it allows the telnetd(8) to detect tty(4) state changes by the slave, and negotiate the appropriate TELNET protocol equivalents with the remote peer.
TIOCUCNTLTIOCPKT.
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.
TIOCREMOTETIOCPKT.
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-zP-T][0-9a-zA-Z]/dev/tty[p-zP-T][0-9a-zA-Z]