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.\" This man page was written by Jeremy Phelps <jphelps@notreached.net>.
.\" Notes added - aeb
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.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 \fI/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 \fI/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 \fI/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),
.BR pty (7)