ptmx(4) — Linux manual page


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

NAME         top

       ptmx, pts - pseudoterminal master and slave

DESCRIPTION         top

       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

       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

       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

FILES         top

       /dev/ptmx, /dev/pts/*

NOTES         top

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

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

SEE ALSO         top

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

COLOPHON         top

       This page is part of release 5.07 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)

Pages that refer to this page: getpt(3)