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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 pseu-
     doterminal 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  pro-
     vides  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  emula-
     tors  such as xterm(1), in which data read from the pseudoterminal mas-
     ter 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 ter-
     minal or terminal emulator.

     Pseudoterminals can also be used to send input to  programs  that  nor-
     mally 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 nam-
     ing) 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.