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       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

       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)