1PTS(4) Linux Programmer's Manual PTS(4)
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6 ptmx, pts - pseudoterminal master and slave
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9 The file /dev/ptmx is a character file with major number 5 and minor
10 number 2, usually with mode 0666 and ownership root:root. It is used
11 to create a pseudoterminal master and slave pair.
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13 When a process opens /dev/ptmx, it gets a file descriptor for a pseu‐
14 doterminal master (PTM), and a pseudoterminal slave (PTS) device is
15 created in the /dev/pts directory. Each file descriptor obtained by
16 opening /dev/ptmx is an independent PTM with its own associated PTS,
17 whose path can be found by passing the file descriptor to ptsname(3).
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19 Before opening the pseudoterminal slave, you must pass the master's
20 file descriptor to grantpt(3) and unlockpt(3).
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22 Once both the pseudoterminal master and slave are open, the slave pro‐
23 vides processes with an interface that is identical to that of a real
24 terminal.
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26 Data written to the slave is presented on the master file descriptor as
27 input. Data written to the master is presented to the slave as input.
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29 In practice, pseudoterminals are used for implementing terminal emula‐
30 tors such as xterm(1), in which data read from the pseudoterminal mas‐
31 ter is interpreted by the application in the same way a real terminal
32 would interpret the data, and for implementing remote-login programs
33 such as sshd(8), in which data read from the pseudoterminal master is
34 sent across the network to a client program that is connected to a ter‐
35 minal or terminal emulator.
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37 Pseudoterminals can also be used to send input to programs that nor‐
38 mally refuse to read input from pipes (such as su(1), and passwd(1)).
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41 /dev/ptmx, /dev/pts/*
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44 The Linux support for the above (known as UNIX 98 pseudoterminal nam‐
45 ing) is done using the devpts filesystem, that should be mounted on
46 /dev/pts.
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48 Before this UNIX 98 scheme, master pseudoterminals were called
49 /dev/ptyp0, ... and slave pseudoterminals /dev/ttyp0, ... and one
50 needed lots of preallocated device nodes.
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53 getpt(3), grantpt(3), ptsname(3), unlockpt(3), pty(7)
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56 This page is part of release 5.04 of the Linux man-pages project. A
57 description of the project, information about reporting bugs, and the
58 latest version of this page, can be found at
59 https://www.kernel.org/doc/man-pages/.
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63Linux 2016-03-15 PTS(4)