1PTS(4) Linux Programmer's Manual PTS(4)
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6 ptmx and pts - pseudo-terminal 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 of mode 0666 and owner.group of root.root. It is
11 used to create a pseudo-terminal master and slave pair.
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13 When a process opens /dev/ptmx, it gets a file descriptor for a pseudo-
14 terminal master (PTM), and a pseudo-terminal slave (PTS) device is cre‐
15 ated in the /dev/pts directory. Each file descriptor obtained by open‐
16 ing /dev/ptmx is an independent PTM with its own associated PTS, whose
17 path can be found by passing the descriptor to ptsname(3).
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19 Before opening the pseudo-terminal slave, you must pass the master's
20 file descriptor to grantpt(3) and unlockpt(3).
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22 Once both the pseudo-terminal 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 descriptor as
27 input. Data written to the master is presented to the slave as input.
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29 In practice, pseudo-terminals are used for implementing terminal emula‐
30 tors such as xterm(1), in which data read from the pseudo-terminal 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 pseudo-terminal 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 Pseudo-terminals 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 Unix98 pty naming) is done
45 using the devpts file system, that should be mounted on /dev/pts.
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47 Before this Unix98 scheme, master ptys were called /dev/ptyp0, ... and
48 slave ptys /dev/ttyp0, ... and one needed lots of preallocated device
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52 getpt(3), grantpt(3), ptsname(3), unlockpt(3), pty(7)
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55 This page is part of release 3.22 of the Linux man-pages project. A
56 description of the project, and information about reporting bugs, can
57 be found at http://www.kernel.org/doc/man-pages/.
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61Linux 2002-10-09 PTS(4)