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PTMX, PTS - reference manual online

Pseudoterminal master and slave.

Chapter
2002-10-09
PTS(4)                              Linux Programmer's Manual                              PTS(4)

NAME ptmx, pts - pseudoterminal 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 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 associ‐ ated PTS, whose path can be found by passing the 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 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 applica‐ tion 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 passwd(1)).
FILES /dev/ptmx, /dev/pts/*
NOTES 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 getpt(3), grantpt(3), ptsname(3), unlockpt(3), pty(7)
COLOPHON This page is part of release 4.04 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 http://www.kernel.org/doc/man-pages/.
Linux 2002-10-09 PTS(4)
This manual Reference Other manuals
pts(4) referred by getpt(3) | grantpt(3) | posix_openpt(2freebsd) | posix_openpt(3) | proc(5) | pts(4freebsd) | ptsname(3) | pty(4freebsd) | pty(7) | unlockpt(3)
refer to getpt(3) | grantpt(3) | passwd(1) | ptsname(3) | pty(7) | sshd(8) | su(1) | unlockpt(3) | xterm(1)