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pts(4) Kernel Interfaces Manual pts(4)
ptmx, pts - pseudoterminal master and slave
The file /dev/ptmx (the pseudoterminal multiplexor device) 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 and a pseudoterminal slave device is created
in the /dev/pts directory. Each file descriptor obtained by
opening /dev/ptmx is an independent pseudoterminal master with its
own associated slave, 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
passwd(1)).
/dev/ptmx, /dev/pts/*
The Linux support for the above (known as UNIX 98 pseudoterminal
naming) is done using the devpts filesystem, which should be
mounted on /dev/pts.
getpt(3), grantpt(3), ptsname(3), unlockpt(3), pty(7)
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Linux man-pages 6.15 2025-05-17 pts(4)
Pages that refer to this page: getpt(3), grantpt(3), posix_openpt(3), ptsname(3), ttyname(3), unlockpt(3), proc_sys_kernel(5), pty(7)
Copyright and license for this manual page
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