PTS(4) Linux Programmer's Manual PTS(4)
ptmx, pts - pseudoterminal master and slave
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 file 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 file 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 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
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)).
/dev/ptmx, /dev/pts/*
The Linux support for the above (known as UNIX 98 pseudoterminal
naming) is done using the devpts filesystem, 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.
getpt(3), grantpt(3), ptsname(3), unlockpt(3), pty(7)
This page is part of release 4.12 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
Linux 2016-03-15 PTS(4)
Pages that refer to this page: getpt(3), grantpt(3), posix_openpt(3), ptsname(3), ttyname(3), unlockpt(3), proc(5), pty(7)