1PTS(4)                     Linux Programmer's Manual                    PTS(4)
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NAME

6       ptmx, pts - pseudo-terminal master and slave
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DESCRIPTION

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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FILES

41       /dev/ptmx, /dev/pts/*
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NOTES

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
49       nodes.
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SEE ALSO

52       getpt(3), grantpt(3), ptsname(3), unlockpt(3), pty(7)
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COLOPHON

55       This  page  is  part of release 3.25 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)
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