mirror of https://github.com/mkerrisk/man-pages
71 lines
2.3 KiB
Groff
71 lines
2.3 KiB
Groff
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.\" Hey Emacs! This file is -*- nroff -*- source.
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.\" This man page was written by Jeremy Phelps <jphelps@notreached.net>.
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.\" Notes added - aeb
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.\" Redistribute and revise at will.
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.\"
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.TH PTS 4 "2002-10-09" "Linux" "Linux Programmer's Manual"
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.SH NAME
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ptmx and pts \- pseudo-terminal master and slave
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.SH DESCRIPTION
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The file \fB/dev/ptmx\fP is a character file with major number 5 and
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minor number 2, usually of mode 0666 and owner.group of root.root.
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It is used to create a pseudo-terminal master and slave pair.
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.PP
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When a process opens \fB/dev/ptmx\fP, it gets a file
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descriptor for a pseudo-terminal master (PTM),
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and a pseudo-terminal slave (PTS) device is created in the
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.I /dev/pts
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directory. Each file descriptor obtained by opening \fB/dev/ptmx\fP
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is an independent PTM with its own associated PTS, whose path can
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be found by passing the descriptor to
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.BR ptsname (3).
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.PP
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Before opening the pseudo-terminal slave, you must pass the master's file
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descriptor to
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.BR grantpt (3)
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and
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.BR unlockpt (3).
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.PP
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Once both the pseudo-terminal master and slave are open, the slave provides
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processes with an interface that is identical to that of a real terminal.
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.PP
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Data written to the slave is presented on the master descriptor as input.
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Data written to the master is presented to the slave as input.
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.PP
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In practice, pseudo-terminals are used for implementing terminal emulators
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such as
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.BR xterm (1),
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in which data read from the pseudo-terminal master is interpreted by the
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application in the same way
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a real terminal would interpret the data, and for implementing remote-login
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programs such as
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.BR sshd (8),
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in which data read from the pseudo-terminal master is sent across the network
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to a client program that is connected to a terminal or terminal emulator.
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.PP
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Pseudo-terminals can also be used to send input to programs that normally
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refuse to read input from pipes (such as
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.BR su (8),
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and
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.BR passwd (8)).
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.SH FILES
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.IR /dev/ptmx ,
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.I /dev/pts/*
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.SH NOTES
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The Linux support for the above (known as Unix98 pty naming)
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is done using the
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.I devpts
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filesystem, that should be mounted on
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.IR /dev/pts .
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.LP
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Before this Unix98 scheme, master ptys were called
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.IR /dev/ptyp0 ", ..."
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and slave ptys
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.IR /dev/ttyp0 ", ..."
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and one needed lots of preallocated device nodes.
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.SH "SEE ALSO"
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.BR getpt (3),
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.BR grantpt (3),
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.BR ptsname (3),
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.BR unlockpt (3)
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