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+.\" Hey Emacs! This file is -*- nroff -*- source.
+.\" This man page was written by Jeremy Phelps <jphelps@notreached.net>.
+.\" Notes added - aeb
+.\" Redistribute and revise at will.
+.\"
+.TH PTS 4 "2002-10-09" "Linux" "Linux Programmer's Manual"
+.SH NAME
+ptmx and pts \- pseudo-terminal master and slave
+.SH DESCRIPTION
+The file \fB/dev/ptmx\fP 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.
+.PP
+When a process opens \fB/dev/ptmx\fP, it gets a file
+descriptor for a pseudo-terminal master (PTM),
+and a pseudo-terminal slave (PTS) device is created in the
+.I /dev/pts
+directory. Each file descriptor obtained by opening \fB/dev/ptmx\fP
+is an independent PTM with its own associated PTS, whose path can
+be found by passing the descriptor to
+.BR ptsname (3).
+.PP
+Before opening the pseudo-terminal slave, you must pass the master's file
+descriptor to
+.BR grantpt (3)
+and
+.BR unlockpt (3).
+.PP
+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.
+.PP
+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.
+.PP
+In practice, pseudo-terminals are used for implementing terminal emulators
+such as 
+.BR 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
+.BR 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.
+.PP
+Pseudo-terminals can also be used to send input to programs that normally
+refuse to read input from pipes (such as
+.BR su (8),
+and
+.BR passwd (8)).
+.SH FILES
+.IR /dev/ptmx ,
+.I /dev/pts/*
+.SH NOTES
+The Linux support for the above (known as Unix98 pty naming)
+is done using the
+.I devpts
+filesystem, that should be mounted on
+.IR /dev/pts .
+.LP
+Before this Unix98 scheme, master ptys were called
+.IR /dev/ptyp0 ", ..."
+and slave ptys
+.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)