.\" This man page was written by Jeremy Phelps <jphelps@notreached.net>.
.\" Notes added - aeb
.\"
.\" %%%LICENSE_START(FREELY_REDISTRIBUTABLE)
.\" Redistribute and revise at will.
.\" %%%LICENSE_END
.\"
.TH pts 4 2022-10-30 "Linux man-pages 6.04"
.SH NAME
ptmx, pts \- pseudoterminal master and slave
.SH DESCRIPTION
The file
.I /dev/ptmx
(the pseudoterminal multiplexor device)
is a character file with major number 5 and
minor number 2, usually with mode 0666 and ownership 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
and a pseudoterminal slave device is created in the
.I /dev/pts
directory.
Each file descriptor obtained by opening
.I /dev/ptmx
is an independent pseudoterminal master with its own associated slave,
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, which should be mounted on
.IR /dev/pts .
.SH SEE ALSO
.BR getpt (3),
.BR grantpt (3),
.BR ptsname (3),
.BR unlockpt (3),
.BR pty (7)