— pseudo-terminal driver
driver provides support for a device-pair termed a
. 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)
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:
- 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:
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
- whenever the read queue for the terminal is
- whenever the write queue for the terminal is
- whenever output to the terminal is stopped a la
- whenever output to the terminal is restarted.
- whenever the start and stop characters are not
^S/^Q’ flow-controlled remote login
with proper back-flushing of output; it can be used by other similar
- Obtain device unit number, which can be used to generate
the filename of the pseudo-terminal slave device. This
ioctl(2) should not be used directly. Instead, the
ptsname(3) function should be used.
- Determine whether the file descriptor is pointing to a
pseudo-terminal master device. This ioctl(2) should not
be used directly. It is used to implement routines like
The maximum number of pseudo-terminals is limited to 1000. It is not possible to
use more than 1000 pseudo-terminals, as all software which use
will not be able to handle pseudo-terminals with
number superior to 999.
The files used by this pseudo-terminals implementation are:
- Control device, returns a file descriptor to a new master
pseudo-terminal when opened. This device should not be opened directly.
It's only available for binary compatibility. New devices should only be
allocated with posix_openpt(2) and
- Pseudo-terminal slave devices.
The following sysctl(8)
variables can be used to modify or
- Highest pseudo-terminal unit number to be allocated.
Because utmp(5) is restricted to an 8-byte line name
size, pts will not create any pseudo-terminals with a
unit number above 999 by default. After increasing
UT_LINESIZE, this variable can be changed to allow
more than 1000 pseudo-terminals to be allocated simultaneously.
A pseudo-terminal driver appeared in 4.2BSD
, it was replaced with the