mirror of https://github.com/mkerrisk/man-pages
76 lines
2.2 KiB
Groff
76 lines
2.2 KiB
Groff
.\" This man page was written by Jeremy Phelps <jphelps@notreached.net>.
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.\" Notes added - aeb
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.\"
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.\" %%%LICENSE_START(FREELY_REDISTRIBUTABLE)
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.\" Redistribute and revise at will.
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.\" %%%LICENSE_END
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.\"
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.TH PTS 4 2020-08-13 "Linux" "Linux Programmer's Manual"
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.SH NAME
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ptmx, pts \- pseudoterminal master and slave
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.SH DESCRIPTION
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The file
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.I /dev/ptmx
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(the pseudoterminal multiplexor device)
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is a character file with major number 5 and
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minor number 2, usually with mode 0666 and ownership root:root.
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It is used to create a pseudoterminal master and slave pair.
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.PP
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When a process opens
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.IR /dev/ptmx ,
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it gets a file
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descriptor for a pseudoterminal master
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and a pseudoterminal slave device is created in the
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.I /dev/pts
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directory.
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Each file descriptor obtained by opening
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.IR /dev/ptmx
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is an independent pseudoterminal master with its own associated slave,
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whose path can
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be found by passing the file descriptor to
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.BR ptsname (3).
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.PP
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Before opening the pseudoterminal 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 pseudoterminal 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 file 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, pseudoterminals 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 pseudoterminal 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 pseudoterminal 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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Pseudoterminals 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 (1),
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and
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.BR passwd (1)).
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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 UNIX 98 pseudoterminal naming)
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is done using the
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.I devpts
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filesystem, which should be mounted on
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.IR /dev/pts .
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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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.BR pty (7)
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