ptmx

DESCRIPTION

       The  file  /dev/ptmx  is a character file with major number 5 and minor

       number 2, usually of mode 0666 and owner.group  of  root.root.   It  is

       used to create a pseudo-terminal master and slave pair.

When a process opens /dev/ptmx, it gets a file descriptor for a pseudo-

       terminal master (PTM), and a pseudo-terminal slave (PTS) device is cre-

       ated in the /dev/pts directory.  Each file descriptor obtained by open-

       ing /dev/ptmx is an independent PTM with its own associated PTS,  whose

       path can be found by passing the descriptor to ptsname(3).
Before  opening  the  pseudo-terminal slave, you must pass the master‘s

       file descriptor to grantpt(3) and unlockpt(3).
Once both the pseudo-terminal master and slave are open, the slave pro-

       vides  processes  with an interface that is identical to that of a real

       terminal.
Data written to the slave is presented  on  the  master  descriptor  as

       input.  Data written to the master is presented to the slave as input.
In practice, pseudo-terminals are used for implementing terminal emula-

       tors such as xterm(1), in which data read from the pseudo-terminal mas-

       ter  is  interpreted by the application in the same way a real terminal

       would interpret the data, and for  implementing  remote-login  programs

       such  as sshd(8), in which data read from the pseudo-terminal master is

       sent across the network to a client program that is connected to a ter-

       minal or terminal emulator.
Pseudo-terminals  can  also be used to send input to programs that nor-

       mally refuse to read input from pipes (such as su(1), and passwd(1)).
FILES

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

       The Linux support for the above (known as Unix98 pty  naming)  is  done

       using the devpts file system, that should be mounted on /dev/pts.
Before this Unix98 scheme, master ptys were called /dev/ptyp0, ...  and

       slave ptys /dev/ttyp0, ...  and one needed lots of preallocated  device

       nodes.
SEE ALSO

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

       This  page  is  part of release 3.23 of the Linux man-pages project.  A

       description of the project, and information about reporting  bugs,  can

       be found at http://www.kernel.org/doc/man-pages/.

ptmx