pty(4) [ultrix man page]

pty(4) Kernel Interfaces Manual pty(4)

Name
pty - 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 manipulating it through the master half of the pseudoterminal. 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 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 /etc/ttys file. This must be done to insure that logins that use pseudoter-
minals will be tracked in the utmp and wtmp 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
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 pseudoterminal, each subsequent from the terminal will return
data written on the slave part of the pseudoterminal 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 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 character is CTRL/Q.

TIOCPKT_NOSTOP
whenever the start and stop characters are not CTRL/S and/or CTRL/Q.

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 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.

TIOCMASTER
Allows the master to have complete control over the pseudoterminal and causes the slave side to sleep until the master relinquishes
control. This is useful in preventing changes on the pseudoterminal from going undetected and being reset by the master.

Files
(master pseudoterminals)

(slave pseudoterminals)

Check Out this Related Man Page

PTS(4)							     Linux Programmer's Manual							    PTS(4)

NAME

       ptmx, pts - pseudoterminal master and slave

DESCRIPTION

       The  file  /dev/ptmx  is a character file with major number 5 and minor number 2, usually of mode 0666 and owner.group of root.root.  It is
       used to create a pseudoterminal master and slave pair.

       When a process opens /dev/ptmx, it gets a file descriptor for a pseudoterminal master (PTM), and a pseudoterminal  slave  (PTS)	device	is
       created	in  the /dev/pts directory.  Each file descriptor obtained by opening /dev/ptmx is an independent PTM with its own associated PTS,
       whose path can be found by passing the descriptor to ptsname(3).

       Before opening the pseudoterminal slave, you must pass the master's file descriptor to grantpt(3) and unlockpt(3).

       Once both the pseudoterminal master and slave are open, the slave provides processes with an interface that is identical to that of a  real
       terminal.

       Data written to the slave is presented on the master descriptor as input.  Data written to the master is presented to the slave as input.

       In practice, pseudoterminals are used for implementing terminal emulators such as xterm(1), in which data read from the pseudoterminal mas-
       ter is interpreted by the application in the same way a real terminal would interpret the data, and for implementing remote-login  programs
       such  as  sshd(8),  in which data read from the pseudoterminal master is sent across the network to a client program that is connected to a
       terminal or terminal emulator.

       Pseudoterminals can also be used to send input to programs that normally refuse to read input from pipes (such as su(1), and passwd(1)).

FILES

       /dev/ptmx, /dev/pts/*

NOTES

       The Linux support for the above (known as UNIX 98 pseudoterminal naming) is done using the devpts file system, that should  be  mounted	on
       /dev/pts.

       Before  this  UNIX 98 scheme, master pseudoterminals were called /dev/ptyp0, ...  and slave pseudoterminals /dev/ttyp0, ...  and one needed
       lots of preallocated device nodes.

SEE ALSO

       getpt(3), grantpt(3), ptsname(3), unlockpt(3), pty(7)

COLOPHON

       This page is part of release 3.53 of the Linux man-pages project.  A description of the project, and information about reporting bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

Linux								    2002-10-09								    PTS(4)

Linux and UNIX Man Pages

pty(4) [ultrix man page]

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