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 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  (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 associated PTS, 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)).

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

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