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

       ptmx, pts - pseudoterminal master and slave

       The file /dev/ptmx is a character file with major number 5 and minor
       number 2, usually with mode 0666 and ownership root:root.  It is used
       to create a pseudoterminal master and slave pair.

       When a process opens /dev/ptmx, it gets a file descriptor for a
       pseudoterminal master (PTM), and a pseudoterminal slave (PTS) device is
       created in the /dev/pts directory.  Each file descriptor obtained by
       opening /dev/ptmx is an independent PTM with its own associated PTS,
       whose path can be found by passing the file descriptor to ptsname(3).

       Before opening the pseudoterminal slave, you must pass the master's
       file descriptor to grantpt(3) and unlockpt(3).

       Once both the pseudoterminal master and slave are open, the slave
       provides processes with an interface that is identical to that of a
       real terminal.

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

       In practice, pseudoterminals are used for implementing terminal
       emulators such as xterm(1), in which data read from the pseudoterminal
       master 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 pseudoterminal
       master is sent across the network to a client program that is connected
       to a terminal or terminal emulator.

       Pseudoterminals can also be used to send input to programs that
       normally refuse to read input from pipes (such as su(1), and

       /dev/ptmx, /dev/pts/*

       The Linux support for the above (known as UNIX 98 pseudoterminal
       naming) is done using the devpts filesystem, that should be mounted on

       Before this UNIX 98 scheme, master pseudoterminals were called
       /dev/ptyp0, ...  and slave pseudoterminals /dev/ttyp0, ...  and one
       needed lots of preallocated device nodes.

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

       This page is part of release 5.03 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

Linux                             2016-03-15                            PTS(4)