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 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 associ‐
       ated 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 provides 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  emulators  such as
       xterm(1), in which data read from the pseudoterminal master is interpreted by the applica‐
       tion  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 3.74 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)