PTS(4)			 BSD Kernel Interfaces Manual			PTS(4)

NAME
     pts — pseudo-terminal driver

DESCRIPTION
     The pts driver provides support for a device-pair termed a
     pseudo-terminal.  A pseudo-terminal is a pair of character devices, a
     master device and a slave device.	The slave device provides to a process
     an interface identical to that described in tty(4).  However, whereas all
     other devices which provide the interface described in tty(4) have a
     hardware device of some sort behind them, the slave device has, instead,
     another process manipulating it through the master half of the pseudo-
     terminal.	That is, anything written on the master device is given to the
     slave device as input and anything written on the slave device is pre‐
     sented as input on the master device.

     The following ioctl(2) calls apply only to pseudo-terminals:

     TIOCPKT	   Enable/disable packet mode.	Packet mode is enabled by
		   specifying (by reference) a nonzero parameter and disabled
		   by specifying (by reference) a zero parameter.  When
		   applied to the master side of a pseudo-terminal, each sub‐
		   sequent read(2) from the terminal will return data written
		   on the slave part of the pseudo-terminal preceded by a zero
		   byte (symbolically defined as TIOCPKT_DATA), or a single
		   byte reflecting control status information.	In the latter
		   case, the byte is an inclusive-or of zero or more of the
		   bits:

		   TIOCPKT_FLUSHREAD   whenever the read queue for the termi‐
				       nal is flushed.

		   TIOCPKT_FLUSHWRITE  whenever the write queue for the termi‐
				       nal is flushed.

		   TIOCPKT_STOP	       whenever output to the terminal is
				       stopped a la ‘^S’.

		   TIOCPKT_START       whenever output to the terminal is
				       restarted.

		   TIOCPKT_DOSTOP      whenever VSTOP is ‘^S’ and VSTART is
				       ‘^Q’.

		   TIOCPKT_NOSTOP      whenever the start and stop characters
				       are not ‘^S/^Q’.

		   While this mode is in use, the presence of control status
		   information to be read from the master side may be detected
		   by a select(2) for exceptional conditions.

		   This mode is used by rlogin(1) and rlogind(8) to implement
		   a remote-echoed, locally ‘^S/^Q’ flow-controlled remote
		   login with proper back-flushing of output; it can be used
		   by other similar programs.

     TIOCGPTN	   Obtain device unit number, which can be used to generate
		   the filename of the pseudo-terminal slave device. This
		   ioctl(2) should not be used directly. Instead, the
		   ptsname(3) function should be used.

     TIOCPTMASTER  Determine whether the file descriptor is pointing to a
		   pseudo-terminal master device.  This ioctl(2) should not be
		   used directly. It is used to implement routines like
		   grantpt(3).

     The maximum number of pseudo-terminals is limited to 1000.	 It is not
     possible to use more than 1000 pseudo-terminals, as all software which
     use utmp(5) will not be able to handle pseudo-terminals with number supe‐
     rior to 999.

FILES
     The files used by this pseudo-terminals implementation are:

     /dev/ptmx	     Control device, returns a file descriptor to a new master
		     pseudo-terminal when opened.  This device should not be
		     opened directly.  It's only available for binary compati‐
		     bility.  New devices should only be allocated with
		     posix_openpt(2) and openpty(3).

     /dev/pts/[num]  Pseudo-terminal slave devices.

SYSCTL VARIABLES
     The following sysctl(8) variables can be used to modify or monitor pts
     behavior.

     kern.pts_maxdev
	     Highest pseudo-terminal unit number to be allocated.  Because
	     utmp(5) is restricted to an 8-byte line name size, pts will not
	     create any pseudo-terminals with a unit number above 999 by
	     default.  After increasing UT_LINESIZE, this variable can be
	     changed to allow more than 1000 pseudo-terminals to be allocated
	     simultaneously.

DIAGNOSTICS
     None.

SEE ALSO
     grantpt(3), posix_openpt(2), ptsname(3), pty(4), tty(4)

HISTORY
     A pseudo-terminal driver appeared in 4.2BSD.  In FreeBSD 8.0, it was
     replaced with the pts driver.

BSD				August 20, 2008				   BSD

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