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.TH PTS 4 2016-03-15 "Linux" "Linux Programmer's Manual"

.SH NAME

ptmx, pts \- pseudoterminal master and slave

.SH DESCRIPTION

The file

.I /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.

.PP

When a process opens

.IR /dev/ptmx ,

it gets a file

descriptor for a pseudoterminal master (PTM),

and a pseudoterminal slave (PTS) device is created in the

.I /dev/pts

directory.

Each file descriptor obtained by opening

.IR /dev/ptmx

is an independent PTM with its own associated PTS, whose path can

be found by passing the file descriptor to

.BR ptsname (3).

.PP

Before opening the pseudoterminal slave, you must pass the master's file

descriptor to

.BR grantpt (3)

and

.BR unlockpt (3).

.PP

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.

.PP

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.

.PP

In practice, pseudoterminals are used for implementing terminal emulators

such as

.BR 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

.BR 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.

.PP

Pseudoterminals can also be used to send input to programs that normally

refuse to read input from pipes (such as

.BR su (1),

and

.BR passwd (1)).

.SH FILES

.IR /dev/ptmx ,

.I /dev/pts/*

.SH NOTES

The Linux support for the above (known as UNIX 98 pseudoterminal naming)

is done using the

.I devpts

filesystem, that should be mounted on

.IR /dev/pts .

.PP

Before this UNIX 98 scheme, master pseudoterminals were called

.IR /dev/ptyp0 ", ..."

and slave pseudoterminals

.IR /dev/ttyp0 ", ..."

and one needed lots of preallocated device nodes.

.SH SEE ALSO

.BR getpt (3),

.BR grantpt (3),

.BR ptsname (3),

.BR unlockpt (3),

.BR pty (7)

.SH COLOPHON

This page is part of release 4.15 of the Linux

.I 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/.