linux man page for ptmx

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  pro-
       grams  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 3.27 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)