pts(4)



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 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  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.

SEE ALSO
       getpt(3), grantpt(3), ptsname(3), unlockpt(3), pty(7)

COLOPHON
       This page is part of release 3.71 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)

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