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ptmx(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
   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

   This  page  is  part of release 4.09 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
   https://www.kernel.org/doc/man-pages/.



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