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



NAME
       ptmx, pts - pseudo-terminal master and slave

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 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 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 provides 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 emulators such as xterm(1), in which data read from  the
       pseudo-terminal  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 pseudo-terminal master is sent across
       the network to a client program that is connected to a terminal or terminal emulator.

       Pseudo-terminals can also be used to send input to programs that normally 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 3.25 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/.



Linux                                                      2002-10-09                                                     PTS(4)