| NAME | DESCRIPTION | FILES | NOTES | SEE ALSO | COLOPHON | The Linux Programming Interface |
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 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 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.
Psuedoterminals 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 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.
getpt(3), grantpt(3), ptsname(3), unlockpt(3), pty(7)
This page is part of release 3.32 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)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface