NAME
ptmx, pts - pseudo-terminal 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 pseudo-terminal master and slave pair.
When a process opens /dev/ptmx, it gets a file descriptor for a pseudo-
terminal master (PTM), and a pseudo-terminal 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 pseudo-terminal slave, you must pass the master’s
file descriptor to grantpt(3) and unlockpt(3).
Once both the pseudo-terminal 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, pseudo-terminals are used for implementing terminal
emulators such as xterm(1), in which data read from the pseudo-terminal
master 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 pseudo-terminal
master is sent across the network to a client program that is connected
to a terminal or terminal emulator.
Pseudo-terminals 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 Unix98 pty naming) is done
using the devpts file system, that should be mounted on /dev/pts.
Before this Unix98 scheme, master ptys were called /dev/ptyp0, ... and
slave ptys /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 3.24 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/.