pty(4)pty(4)Namepty - pseudoterminal driver
Syntax
pseudo-device pty[n]
Description
The driver provides support for a device-pair termed a pseudoterminal.
A pseudoterminal is a pair of character devices, a master device and a
slave device. The slave device provides processes with an interface
identical to that described in However, whereas all other devices that
provide the interface described in have a hardware device of some sort
behind them, the slave device has, instead, another process manipulat‐
ing it through the master half of the pseudoterminal. That is, any‐
thing 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 slave device can be opened multiple times,
while the master half can be opened only once.
If no optional n value is given defining the number of pseudoterminal
pairs to be configured, 16 pseudoterminal pairs are configured. All
pseudoterminal lines should have a corresponding entry in the file.
This must be done to insure that logins that use pseudoterminals are
tracked in the and files.
The following calls apply only to pseudoterminals:
TIOCSTOP
Stops output to a terminal (for example, like typing CTRL/S).
Takes no parameter.
TIOCSTART
Restarts output (stopped by TIOCSTOP or by typing CTRL/S).
Takes no parameter.
TIOCPKT
Enables or disables 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 pseudoterminal, each subsequent from the termi‐
nal will return data written on the slave part of the pseudoter‐
minal preceded by a zero byte (symbolically defined as
TIOCPKT_DATA), or a single byte reflecting control status infor‐
mation. 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 by typing
CTRL/S.
TIOCPKT_START
whenever output to the terminal is restarted.
TIOCPKT_DOSTOP
whenever the stop character is CTRL/S and the start char‐
acter is CTRL/Q.
TIOCPKT_NOSTOP
whenever the start and stop characters are not CTRL/S or
CTRL/Q or both.
This mode is used by and to implement a remote-echoed, locally
flow-controlled (using CTRL/S or CTRL/Q, or both) remote login
with proper back-flushing of output. It can be used by other
similar programs.
TIOCREMOTE
A mode for the master half of a pseudoterminal, independent of
TIOCPKT. This mode causes input to the pseudoterminal 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 termi‐
nal; a write of 0 bytes is like typing an end-of-file character.
TIOCREMOTE can be used when doing remote line editing in a win‐
dow manager, or whenever flow-controlled input is required.
TIOCMASTER
Allows the master to have complete control over the pseudotermi‐
nal and causes the slave side to sleep until the master relin‐
quishes control. This is useful in preventing changes on the
pseudoterminal from going undetected and being reset by the mas‐
ter.
Diagnostics
[EIO] An attempt to open the slave side of the was made
before opening the master side of the
Files
(master pseudoterminals)
(slave pseudoterminals)
See Alsotty(4), MAKEDEV(8)pty(4)
