NAME | DESCRIPTION | FILES | NOTES | SEE ALSO | COLOPHON
PTS(4) Linux Programmer's Manual PTS(4)
ptmx and pts - pseudo-terminal 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
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)).
/dev/ptmx, /dev/pts/*
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.
getpt(3), grantpt(3), ptsname(3), unlockpt(3), pty(7)
This page is part of release 3.23 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)