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PTS(4)			   Linux Programmer's Manual			PTS(4)

       ptmx, pts - pseudoterminal master and slave

       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

       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)).

       /dev/ptmx, /dev/pts/*

       The Linux support for the above (known as UNIX 98  pseudoterminal  nam-
       ing)  is	 done  using  the devpts filesystem, that should be mounted on

       Before  this  UNIX  98  scheme,	master	pseudoterminals	 were	called
       /dev/ptyp0,  ...	  and  slave  pseudoterminals /dev/ttyp0, ...  and one
       needed lots of preallocated device nodes.

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

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Linux				  2016-03-15				PTS(4)